Adding upstream version 115.7.0esr.upstream/115.7.0esrupstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1773 insertions, 0 deletions

diff --git a/intl/icu/source/i18n/rbt_pars.cpp b/intl/icu/source/i18n/rbt_pars.cpp
new file mode 100644
index 0000000000..10482d5edb
--- /dev/null
+++ b/intl/icu/source/i18n/rbt_pars.cpp
@@ -0,0 +1,1773 @@
+// © 2016 and later: Unicode, Inc. and others.
+// License & terms of use: http://www.unicode.org/copyright.html
+/*
+ **********************************************************************
+ *   Copyright (C) 1999-2016, International Business Machines
+ *   Corporation and others.  All Rights Reserved.
+ **********************************************************************
+ *   Date        Name        Description
+ *   11/17/99    aliu        Creation.
+ **********************************************************************
+ */
+
+#include "unicode/utypes.h"
+
+#if !UCONFIG_NO_TRANSLITERATION
+
+#include "unicode/uobject.h"
+#include "unicode/parseerr.h"
+#include "unicode/parsepos.h"
+#include "unicode/putil.h"
+#include "unicode/uchar.h"
+#include "unicode/ustring.h"
+#include "unicode/uniset.h"
+#include "unicode/utf16.h"
+#include "cstring.h"
+#include "funcrepl.h"
+#include "hash.h"
+#include "quant.h"
+#include "rbt.h"
+#include "rbt_data.h"
+#include "rbt_pars.h"
+#include "rbt_rule.h"
+#include "strmatch.h"
+#include "strrepl.h"
+#include "unicode/symtable.h"
+#include "tridpars.h"
+#include "uvector.h"
+#include "hash.h"
+#include "patternprops.h"
+#include "util.h"
+#include "cmemory.h"
+#include "uprops.h"
+#include "putilimp.h"
+
+// Operators
+#define VARIABLE_DEF_OP ((char16_t)0x003D) /*=*/
+#define FORWARD_RULE_OP ((char16_t)0x003E) /*>*/
+#define REVERSE_RULE_OP ((char16_t)0x003C) /*<*/
+#define FWDREV_RULE_OP  ((char16_t)0x007E) /*~*/ // internal rep of <> op
+
+// Other special characters
+#define QUOTE             ((char16_t)0x0027) /*'*/
+#define ESCAPE            ((char16_t)0x005C) /*\*/
+#define END_OF_RULE       ((char16_t)0x003B) /*;*/
+#define RULE_COMMENT_CHAR ((char16_t)0x0023) /*#*/
+
+#define SEGMENT_OPEN       ((char16_t)0x0028) /*(*/
+#define SEGMENT_CLOSE      ((char16_t)0x0029) /*)*/
+#define CONTEXT_ANTE       ((char16_t)0x007B) /*{*/
+#define CONTEXT_POST       ((char16_t)0x007D) /*}*/
+#define CURSOR_POS         ((char16_t)0x007C) /*|*/
+#define CURSOR_OFFSET      ((char16_t)0x0040) /*@*/
+#define ANCHOR_START       ((char16_t)0x005E) /*^*/
+#define KLEENE_STAR        ((char16_t)0x002A) /***/
+#define ONE_OR_MORE        ((char16_t)0x002B) /*+*/
+#define ZERO_OR_ONE        ((char16_t)0x003F) /*?*/
+
+#define DOT                ((char16_t)46)     /*.*/
+
+static const char16_t DOT_SET[] = { // "[^[:Zp:][:Zl:]\r\n$]";
+    91, 94, 91, 58, 90, 112, 58, 93, 91, 58, 90,
+    108, 58, 93, 92, 114, 92, 110, 36, 93, 0
+};
+
+// A function is denoted &Source-Target/Variant(text)
+#define FUNCTION           ((char16_t)38)     /*&*/
+
+// Aliases for some of the syntax characters. These are provided so
+// transliteration rules can be expressed in XML without clashing with
+// XML syntax characters '<', '>', and '&'.
+#define ALT_REVERSE_RULE_OP ((char16_t)0x2190) // Left Arrow
+#define ALT_FORWARD_RULE_OP ((char16_t)0x2192) // Right Arrow
+#define ALT_FWDREV_RULE_OP  ((char16_t)0x2194) // Left Right Arrow
+#define ALT_FUNCTION        ((char16_t)0x2206) // Increment (~Greek Capital Delta)
+
+// Special characters disallowed at the top level
+static const char16_t ILLEGAL_TOP[] = {41,0}; // ")"
+
+// Special characters disallowed within a segment
+static const char16_t ILLEGAL_SEG[] = {123,125,124,64,0}; // "{}|@"
+
+// Special characters disallowed within a function argument
+static const char16_t ILLEGAL_FUNC[] = {94,40,46,42,43,63,123,125,124,64,0}; // "^(.*+?{}|@"
+
+// By definition, the ANCHOR_END special character is a
+// trailing SymbolTable.SYMBOL_REF character.
+// private static final char ANCHOR_END       = '$';
+
+static const char16_t gOPERATORS[] = { // "=><"
+    VARIABLE_DEF_OP, FORWARD_RULE_OP, REVERSE_RULE_OP,
+    ALT_FORWARD_RULE_OP, ALT_REVERSE_RULE_OP, ALT_FWDREV_RULE_OP,
+    0
+};
+
+static const char16_t HALF_ENDERS[] = { // "=><;"
+    VARIABLE_DEF_OP, FORWARD_RULE_OP, REVERSE_RULE_OP,
+    ALT_FORWARD_RULE_OP, ALT_REVERSE_RULE_OP, ALT_FWDREV_RULE_OP,
+    END_OF_RULE,
+    0
+};
+
+// These are also used in Transliterator::toRules()
+static const int32_t ID_TOKEN_LEN = 2;
+static const char16_t   ID_TOKEN[]   = { 0x3A, 0x3A }; // ':', ':'
+
+/*
+commented out until we do real ::BEGIN/::END functionality
+static const int32_t BEGIN_TOKEN_LEN = 5;
+static const char16_t BEGIN_TOKEN[] = { 0x42, 0x45, 0x47, 0x49, 0x4e }; // 'BEGIN'
+
+static const int32_t END_TOKEN_LEN = 3;
+static const char16_t END_TOKEN[] = { 0x45, 0x4e, 0x44 }; // 'END'
+*/
+
+U_NAMESPACE_BEGIN
+
+//----------------------------------------------------------------------
+// BEGIN ParseData
+//----------------------------------------------------------------------
+
+/**
+ * This class implements the SymbolTable interface.  It is used
+ * during parsing to give UnicodeSet access to variables that
+ * have been defined so far.  Note that it uses variablesVector,
+ * _not_ data.setVariables.
+ */
+class ParseData : public UMemory, public SymbolTable {
+public:
+    const TransliterationRuleData* data; // alias
+
+    const UVector* variablesVector; // alias
+
+    const Hashtable* variableNames; // alias
+
+    ParseData(const TransliterationRuleData* data = 0,
+              const UVector* variablesVector = 0,
+              const Hashtable* variableNames = 0);
+
+    virtual ~ParseData();
+
+    virtual const UnicodeString* lookup(const UnicodeString& s) const override;
+
+    virtual const UnicodeFunctor* lookupMatcher(UChar32 ch) const override;
+
+    virtual UnicodeString parseReference(const UnicodeString& text,
+                                         ParsePosition& pos, int32_t limit) const override;
+    /**
+     * Return true if the given character is a matcher standin or a plain
+     * character (non standin).
+     */
+    UBool isMatcher(UChar32 ch);
+
+    /**
+     * Return true if the given character is a replacer standin or a plain
+     * character (non standin).
+     */
+    UBool isReplacer(UChar32 ch);
+
+private:
+    ParseData(const ParseData &other); // forbid copying of this class
+    ParseData &operator=(const ParseData &other); // forbid copying of this class
+};
+
+ParseData::ParseData(const TransliterationRuleData* d,
+                     const UVector* sets,
+                     const Hashtable* vNames) :
+    data(d), variablesVector(sets), variableNames(vNames) {}
+
+ParseData::~ParseData() {}
+
+/**
+ * Implement SymbolTable API.
+ */
+const UnicodeString* ParseData::lookup(const UnicodeString& name) const {
+    return (const UnicodeString*) variableNames->get(name);
+}
+
+/**
+ * Implement SymbolTable API.
+ */
+const UnicodeFunctor* ParseData::lookupMatcher(UChar32 ch) const {
+    // Note that we cannot use data.lookupSet() because the
+    // set array has not been constructed yet.
+    const UnicodeFunctor* set = nullptr;
+    int32_t i = ch - data->variablesBase;
+    if (i >= 0 && i < variablesVector->size()) {
+        int32_t j = ch - data->variablesBase;
+        set = (j < variablesVector->size()) ?
+            (UnicodeFunctor*) variablesVector->elementAt(j) : 0;
+    }
+    return set;
+}
+
+/**
+ * Implement SymbolTable API.  Parse out a symbol reference
+ * name.
+ */
+UnicodeString ParseData::parseReference(const UnicodeString& text,
+                                        ParsePosition& pos, int32_t limit) const {
+    int32_t start = pos.getIndex();
+    int32_t i = start;
+    UnicodeString result;
+    while (i < limit) {
+        char16_t c = text.charAt(i);
+        if ((i==start && !u_isIDStart(c)) || !u_isIDPart(c)) {
+            break;
+        }
+        ++i;
+    }
+    if (i == start) { // No valid name chars
+        return result; // Indicate failure with empty string
+    }
+    pos.setIndex(i);
+    text.extractBetween(start, i, result);
+    return result;
+}
+
+UBool ParseData::isMatcher(UChar32 ch) {
+    // Note that we cannot use data.lookup() because the
+    // set array has not been constructed yet.
+    int32_t i = ch - data->variablesBase;
+    if (i >= 0 && i < variablesVector->size()) {
+        UnicodeFunctor *f = (UnicodeFunctor*) variablesVector->elementAt(i);
+        return f != nullptr && f->toMatcher() != nullptr;
+    }
+    return true;
+}
+
+/**
+ * Return true if the given character is a replacer standin or a plain
+ * character (non standin).
+ */
+UBool ParseData::isReplacer(UChar32 ch) {
+    // Note that we cannot use data.lookup() because the
+    // set array has not been constructed yet.
+    int i = ch - data->variablesBase;
+    if (i >= 0 && i < variablesVector->size()) {
+        UnicodeFunctor *f = (UnicodeFunctor*) variablesVector->elementAt(i);
+        return f != nullptr && f->toReplacer() != nullptr;
+    }
+    return true;
+}
+
+//----------------------------------------------------------------------
+// BEGIN RuleHalf
+//----------------------------------------------------------------------
+
+/**
+ * A class representing one side of a rule.  This class knows how to
+ * parse half of a rule.  It is tightly coupled to the method
+ * RuleBasedTransliterator.Parser.parseRule().
+ */
+class RuleHalf : public UMemory {
+
+public:
+
+    UnicodeString text;
+
+    int32_t cursor; // position of cursor in text
+    int32_t ante;   // position of ante context marker '{' in text
+    int32_t post;   // position of post context marker '}' in text
+
+    // Record the offset to the cursor either to the left or to the
+    // right of the key.  This is indicated by characters on the output
+    // side that allow the cursor to be positioned arbitrarily within
+    // the matching text.  For example, abc{def} > | @@@ xyz; changes
+    // def to xyz and moves the cursor to before abc.  Offset characters
+    // must be at the start or end, and they cannot move the cursor past
+    // the ante- or postcontext text.  Placeholders are only valid in
+    // output text.  The length of the ante and post context is
+    // determined at runtime, because of supplementals and quantifiers.
+    int32_t cursorOffset; // only nonzero on output side
+
+    // Position of first CURSOR_OFFSET on _right_.  This will be -1
+    // for |@, -2 for |@@, etc., and 1 for @|, 2 for @@|, etc.
+    int32_t cursorOffsetPos;
+
+    UBool anchorStart;
+    UBool anchorEnd;
+
+    /**
+     * The segment number from 1..n of the next '(' we see
+     * during parsing; 1-based.
+     */
+    int32_t nextSegmentNumber;
+
+    TransliteratorParser& parser;
+
+    //--------------------------------------------------
+    // Methods
+
+    RuleHalf(TransliteratorParser& parser);
+    ~RuleHalf();
+
+    int32_t parse(const UnicodeString& rule, int32_t pos, int32_t limit, UErrorCode& status);
+
+    int32_t parseSection(const UnicodeString& rule, int32_t pos, int32_t limit,
+                         UnicodeString& buf,
+                         const UnicodeString& illegal,
+                         UBool isSegment,
+                         UErrorCode& status);
+
+    /**
+     * Remove context.
+     */
+    void removeContext();
+
+    /**
+     * Return true if this half looks like valid output, that is, does not
+     * contain quantifiers or other special input-only elements.
+     */
+    UBool isValidOutput(TransliteratorParser& parser);
+
+    /**
+     * Return true if this half looks like valid input, that is, does not
+     * contain functions or other special output-only elements.
+     */
+    UBool isValidInput(TransliteratorParser& parser);
+
+    int syntaxError(UErrorCode code,
+                    const UnicodeString& rule,
+                    int32_t start,
+                    UErrorCode& status) {
+        return parser.syntaxError(code, rule, start, status);
+    }
+
+private:
+    // Disallowed methods; no impl.
+    RuleHalf(const RuleHalf&);
+    RuleHalf& operator=(const RuleHalf&);
+};
+
+RuleHalf::RuleHalf(TransliteratorParser& p) :
+    parser(p)
+{
+    cursor = -1;
+    ante = -1;
+    post = -1;
+    cursorOffset = 0;
+    cursorOffsetPos = 0;
+    anchorStart = anchorEnd = false;
+    nextSegmentNumber = 1;
+}
+
+RuleHalf::~RuleHalf() {
+}
+
+/**
+ * Parse one side of a rule, stopping at either the limit,
+ * the END_OF_RULE character, or an operator.
+ * @return the index after the terminating character, or
+ * if limit was reached, limit
+ */
+int32_t RuleHalf::parse(const UnicodeString& rule, int32_t pos, int32_t limit, UErrorCode& status) {
+    int32_t start = pos;
+    text.truncate(0);
+    pos = parseSection(rule, pos, limit, text, UnicodeString(true, ILLEGAL_TOP, -1), false, status);
+
+    if (cursorOffset > 0 && cursor != cursorOffsetPos) {
+        return syntaxError(U_MISPLACED_CURSOR_OFFSET, rule, start, status);
+    }
+    
+    return pos;
+}
+ 
+/**
+ * Parse a section of one side of a rule, stopping at either
+ * the limit, the END_OF_RULE character, an operator, or a
+ * segment close character.  This method parses both a
+ * top-level rule half and a segment within such a rule half.
+ * It calls itself recursively to parse segments and nested
+ * segments.
+ * @param buf buffer into which to accumulate the rule pattern
+ * characters, either literal characters from the rule or
+ * standins for UnicodeMatcher objects including segments.
+ * @param illegal the set of special characters that is illegal during
+ * this parse.
+ * @param isSegment if true, then we've already seen a '(' and
+ * pos on entry points right after it.  Accumulate everything
+ * up to the closing ')', put it in a segment matcher object,
+ * generate a standin for it, and add the standin to buf.  As
+ * a side effect, update the segments vector with a reference
+ * to the segment matcher.  This works recursively for nested
+ * segments.  If isSegment is false, just accumulate
+ * characters into buf.
+ * @return the index after the terminating character, or
+ * if limit was reached, limit
+ */
+int32_t RuleHalf::parseSection(const UnicodeString& rule, int32_t pos, int32_t limit,
+                               UnicodeString& buf,
+                               const UnicodeString& illegal,
+                               UBool isSegment, UErrorCode& status) {
+    int32_t start = pos;
+    ParsePosition pp;
+    UnicodeString scratch;
+    UBool done = false;
+    int32_t quoteStart = -1; // Most recent 'single quoted string'
+    int32_t quoteLimit = -1;
+    int32_t varStart = -1; // Most recent $variableReference
+    int32_t varLimit = -1;
+    int32_t bufStart = buf.length();
+    
+    while (pos < limit && !done) {
+        // Since all syntax characters are in the BMP, fetching
+        // 16-bit code units suffices here.
+        char16_t c = rule.charAt(pos++);
+        if (PatternProps::isWhiteSpace(c)) {
+            // Ignore whitespace.  Note that this is not Unicode
+            // spaces, but Java spaces -- a subset, representing
+            // whitespace likely to be seen in code.
+            continue;
+        }
+        if (u_strchr(HALF_ENDERS, c) != nullptr) {
+            if (isSegment) {
+                // Unclosed segment
+                return syntaxError(U_UNCLOSED_SEGMENT, rule, start, status);
+            }
+            break;
+        }
+        if (anchorEnd) {
+            // Text after a presumed end anchor is a syntax err
+            return syntaxError(U_MALFORMED_VARIABLE_REFERENCE, rule, start, status);
+        }
+        if (UnicodeSet::resemblesPattern(rule, pos-1)) {
+            pp.setIndex(pos-1); // Backup to opening '['
+            buf.append(parser.parseSet(rule, pp, status));
+            if (U_FAILURE(status)) {
+                return syntaxError(U_MALFORMED_SET, rule, start, status);
+            }
+            pos = pp.getIndex();                    
+            continue;
+        }
+        // Handle escapes
+        if (c == ESCAPE) {
+            if (pos == limit) {
+                return syntaxError(U_TRAILING_BACKSLASH, rule, start, status);
+            }
+            UChar32 escaped = rule.unescapeAt(pos); // pos is already past '\\'
+            if (escaped == (UChar32) -1) {
+                return syntaxError(U_MALFORMED_UNICODE_ESCAPE, rule, start, status);
+            }
+            if (!parser.checkVariableRange(escaped)) {
+                return syntaxError(U_VARIABLE_RANGE_OVERLAP, rule, start, status);
+            }
+            buf.append(escaped);
+            continue;
+        }
+        // Handle quoted matter
+        if (c == QUOTE) {
+            int32_t iq = rule.indexOf(QUOTE, pos);
+            if (iq == pos) {
+                buf.append(c); // Parse [''] outside quotes as [']
+                ++pos;
+            } else {
+                /* This loop picks up a run of quoted text of the
+                 * form 'aaaa' each time through.  If this run
+                 * hasn't really ended ('aaaa''bbbb') then it keeps
+                 * looping, each time adding on a new run.  When it
+                 * reaches the final quote it breaks.
+                 */
+                quoteStart = buf.length();
+                for (;;) {
+                    if (iq < 0) {
+                        return syntaxError(U_UNTERMINATED_QUOTE, rule, start, status);
+                    }
+                    scratch.truncate(0);
+                    rule.extractBetween(pos, iq, scratch);
+                    buf.append(scratch);
+                    pos = iq+1;
+                    if (pos < limit && rule.charAt(pos) == QUOTE) {
+                        // Parse [''] inside quotes as [']
+                        iq = rule.indexOf(QUOTE, pos+1);
+                        // Continue looping
+                    } else {
+                        break;
+                    }
+                }
+                quoteLimit = buf.length();
+
+                for (iq=quoteStart; iq<quoteLimit; ++iq) {
+                    if (!parser.checkVariableRange(buf.charAt(iq))) {
+                        return syntaxError(U_VARIABLE_RANGE_OVERLAP, rule, start, status);
+                    }
+                }
+            }
+            continue;
+        }
+
+        if (!parser.checkVariableRange(c)) {
+            return syntaxError(U_VARIABLE_RANGE_OVERLAP, rule, start, status);
+        }
+
+        if (illegal.indexOf(c) >= 0) {
+            syntaxError(U_ILLEGAL_CHARACTER, rule, start, status);
+        }
+
+        switch (c) {
+                    
+        //------------------------------------------------------
+        // Elements allowed within and out of segments
+        //------------------------------------------------------
+        case ANCHOR_START:
+            if (buf.length() == 0 && !anchorStart) {
+                anchorStart = true;
+            } else {
+              return syntaxError(U_MISPLACED_ANCHOR_START,
+                                 rule, start, status);
+            }
+          break;
+        case SEGMENT_OPEN:
+            {
+                // bufSegStart is the offset in buf to the first
+                // character of the segment we are parsing.
+                int32_t bufSegStart = buf.length();
+                
+                // Record segment number now, since nextSegmentNumber
+                // will be incremented during the call to parseSection
+                // if there are nested segments.
+                int32_t segmentNumber = nextSegmentNumber++; // 1-based
+                
+                // Parse the segment
+                pos = parseSection(rule, pos, limit, buf, UnicodeString(true, ILLEGAL_SEG, -1), true, status);
+                
+                // After parsing a segment, the relevant characters are
+                // in buf, starting at offset bufSegStart.  Extract them
+                // into a string matcher, and replace them with a
+                // standin for that matcher.
+                StringMatcher* m =
+                    new StringMatcher(buf, bufSegStart, buf.length(),
+                                      segmentNumber, *parser.curData);
+                if (m == nullptr) {
+                    return syntaxError(U_MEMORY_ALLOCATION_ERROR, rule, start, status);
+                }
+                
+                // Record and associate object and segment number
+                parser.setSegmentObject(segmentNumber, m, status);
+                buf.truncate(bufSegStart);
+                buf.append(parser.getSegmentStandin(segmentNumber, status));
+            }
+            break;
+        case FUNCTION:
+        case ALT_FUNCTION:
+            {
+                int32_t iref = pos;
+                TransliteratorIDParser::SingleID* single =
+                    TransliteratorIDParser::parseFilterID(rule, iref);
+                // The next character MUST be a segment open
+                if (single == nullptr ||
+                    !ICU_Utility::parseChar(rule, iref, SEGMENT_OPEN)) {
+                    return syntaxError(U_INVALID_FUNCTION, rule, start, status);
+                }
+                
+                Transliterator *t = single->createInstance();
+                delete single;
+                if (t == nullptr) {
+                    return syntaxError(U_INVALID_FUNCTION, rule, start, status);
+                }
+                
+                // bufSegStart is the offset in buf to the first
+                // character of the segment we are parsing.
+                int32_t bufSegStart = buf.length();
+                
+                // Parse the segment
+                pos = parseSection(rule, iref, limit, buf, UnicodeString(true, ILLEGAL_FUNC, -1), true, status);
+                
+                // After parsing a segment, the relevant characters are
+                // in buf, starting at offset bufSegStart.
+                UnicodeString output;
+                buf.extractBetween(bufSegStart, buf.length(), output);
+                FunctionReplacer *r =
+                    new FunctionReplacer(t, new StringReplacer(output, parser.curData));
+                if (r == nullptr) {
+                    return syntaxError(U_MEMORY_ALLOCATION_ERROR, rule, start, status);
+                }
+                
+                // Replace the buffer contents with a stand-in
+                buf.truncate(bufSegStart);
+                buf.append(parser.generateStandInFor(r, status));
+            }
+            break;
+        case SymbolTable::SYMBOL_REF:
+            // Handle variable references and segment references "$1" .. "$9"
+            {
+                // A variable reference must be followed immediately
+                // by a Unicode identifier start and zero or more
+                // Unicode identifier part characters, or by a digit
+                // 1..9 if it is a segment reference.
+                if (pos == limit) {
+                    // A variable ref character at the end acts as
+                    // an anchor to the context limit, as in perl.
+                    anchorEnd = true;
+                    break;
+                }
+                // Parse "$1" "$2" .. "$9" .. (no upper limit)
+                c = rule.charAt(pos);
+                int32_t r = u_digit(c, 10);
+                if (r >= 1 && r <= 9) {
+                    r = ICU_Utility::parseNumber(rule, pos, 10);
+                    if (r < 0) {
+                        return syntaxError(U_UNDEFINED_SEGMENT_REFERENCE,
+                                           rule, start, status);
+                    }
+                    buf.append(parser.getSegmentStandin(r, status));
+                } else {
+                    pp.setIndex(pos);
+                    UnicodeString name = parser.parseData->
+                                    parseReference(rule, pp, limit);
+                    if (name.length() == 0) {
+                        // This means the '$' was not followed by a
+                        // valid name.  Try to interpret it as an
+                        // end anchor then.  If this also doesn't work
+                        // (if we see a following character) then signal
+                        // an error.
+                        anchorEnd = true;
+                        break;
+                    }
+                    pos = pp.getIndex();
+                    // If this is a variable definition statement,
+                    // then the LHS variable will be undefined.  In
+                    // that case appendVariableDef() will append the
+                    // special placeholder char variableLimit-1.
+                    varStart = buf.length();
+                    parser.appendVariableDef(name, buf, status);
+                    varLimit = buf.length();
+                }
+            }
+            break;
+        case DOT:
+            buf.append(parser.getDotStandIn(status));
+            break;
+        case KLEENE_STAR:
+        case ONE_OR_MORE:
+        case ZERO_OR_ONE:
+            // Quantifiers.  We handle single characters, quoted strings,
+            // variable references, and segments.
+            //  a+      matches  aaa
+            //  'foo'+  matches  foofoofoo
+            //  $v+     matches  xyxyxy if $v == xy
+            //  (seg)+  matches  segsegseg
+            {
+                if (isSegment && buf.length() == bufStart) {
+                    // The */+ immediately follows '('
+                    return syntaxError(U_MISPLACED_QUANTIFIER, rule, start, status);
+                }
+
+                int32_t qstart, qlimit;
+                // The */+ follows an isolated character or quote
+                // or variable reference
+                if (buf.length() == quoteLimit) {
+                    // The */+ follows a 'quoted string'
+                    qstart = quoteStart;
+                    qlimit = quoteLimit;
+                } else if (buf.length() == varLimit) {
+                    // The */+ follows a $variableReference
+                    qstart = varStart;
+                    qlimit = varLimit;
+                } else {
+                    // The */+ follows a single character, possibly
+                    // a segment standin
+                    qstart = buf.length() - 1;
+                    qlimit = qstart + 1;
+                }
+
+                UnicodeFunctor *m =
+                    new StringMatcher(buf, qstart, qlimit, 0, *parser.curData);
+                if (m == nullptr) {
+                    return syntaxError(U_MEMORY_ALLOCATION_ERROR, rule, start, status);
+                }
+                int32_t min = 0;
+                int32_t max = Quantifier::MAX;
+                switch (c) {
+                case ONE_OR_MORE:
+                    min = 1;
+                    break;
+                case ZERO_OR_ONE:
+                    min = 0;
+                    max = 1;
+                    break;
+                // case KLEENE_STAR:
+                //    do nothing -- min, max already set
+                }
+                m = new Quantifier(m, min, max);
+                if (m == nullptr) {
+                    return syntaxError(U_MEMORY_ALLOCATION_ERROR, rule, start, status);
+                }
+                buf.truncate(qstart);
+                buf.append(parser.generateStandInFor(m, status));
+            }
+            break;
+
+        //------------------------------------------------------
+        // Elements allowed ONLY WITHIN segments
+        //------------------------------------------------------
+        case SEGMENT_CLOSE:
+            // assert(isSegment);
+            // We're done parsing a segment.
+            done = true;
+            break;
+
+        //------------------------------------------------------
+        // Elements allowed ONLY OUTSIDE segments
+        //------------------------------------------------------
+        case CONTEXT_ANTE:
+            if (ante >= 0) {
+                return syntaxError(U_MULTIPLE_ANTE_CONTEXTS, rule, start, status);
+            }
+            ante = buf.length();
+            break;
+        case CONTEXT_POST:
+            if (post >= 0) {
+                return syntaxError(U_MULTIPLE_POST_CONTEXTS, rule, start, status);
+            }
+            post = buf.length();
+            break;
+        case CURSOR_POS:
+            if (cursor >= 0) {
+                return syntaxError(U_MULTIPLE_CURSORS, rule, start, status);
+            }
+            cursor = buf.length();
+            break;
+        case CURSOR_OFFSET:
+            if (cursorOffset < 0) {
+                if (buf.length() > 0) {
+                    return syntaxError(U_MISPLACED_CURSOR_OFFSET, rule, start, status);
+                }
+                --cursorOffset;
+            } else if (cursorOffset > 0) {
+                if (buf.length() != cursorOffsetPos || cursor >= 0) {
+                    return syntaxError(U_MISPLACED_CURSOR_OFFSET, rule, start, status);
+                }
+                ++cursorOffset;
+            } else {
+                if (cursor == 0 && buf.length() == 0) {
+                    cursorOffset = -1;
+                } else if (cursor < 0) {
+                    cursorOffsetPos = buf.length();
+                    cursorOffset = 1;
+                } else {
+                    return syntaxError(U_MISPLACED_CURSOR_OFFSET, rule, start, status);
+                }
+            }
+            break;
+
+
+        //------------------------------------------------------
+        // Non-special characters
+        //------------------------------------------------------
+        default:
+            // Disallow unquoted characters other than [0-9A-Za-z]
+            // in the printable ASCII range.  These characters are
+            // reserved for possible future use.
+            if (c >= 0x0021 && c <= 0x007E &&
+                !((c >= 0x0030/*'0'*/ && c <= 0x0039/*'9'*/) ||
+                  (c >= 0x0041/*'A'*/ && c <= 0x005A/*'Z'*/) ||
+                  (c >= 0x0061/*'a'*/ && c <= 0x007A/*'z'*/))) {
+                return syntaxError(U_UNQUOTED_SPECIAL, rule, start, status);
+            }
+            buf.append(c);
+            break;
+        }
+    }
+
+    return pos;
+}
+
+/**
+ * Remove context.
+ */
+void RuleHalf::removeContext() {
+    //text = text.substring(ante < 0 ? 0 : ante,
+    //                      post < 0 ? text.length() : post);
+    if (post >= 0) {
+        text.remove(post);
+    }
+    if (ante >= 0) {
+        text.removeBetween(0, ante);
+    }
+    ante = post = -1;
+    anchorStart = anchorEnd = false;
+}
+
+/**
+ * Return true if this half looks like valid output, that is, does not
+ * contain quantifiers or other special input-only elements.
+ */
+UBool RuleHalf::isValidOutput(TransliteratorParser& transParser) {
+    for (int32_t i=0; i<text.length(); ) {
+        UChar32 c = text.char32At(i);
+        i += U16_LENGTH(c);
+        if (!transParser.parseData->isReplacer(c)) {
+            return false;
+        }
+    }
+    return true;
+}
+
+/**
+ * Return true if this half looks like valid input, that is, does not
+ * contain functions or other special output-only elements.
+ */
+UBool RuleHalf::isValidInput(TransliteratorParser& transParser) {
+    for (int32_t i=0; i<text.length(); ) {
+        UChar32 c = text.char32At(i);
+        i += U16_LENGTH(c);
+        if (!transParser.parseData->isMatcher(c)) {
+            return false;
+        }
+    }
+    return true;
+}
+
+//----------------------------------------------------------------------
+// PUBLIC API
+//----------------------------------------------------------------------
+
+/**
+ * Constructor.
+ */
+TransliteratorParser::TransliteratorParser(UErrorCode &statusReturn) :
+dataVector(statusReturn),
+idBlockVector(statusReturn),
+variablesVector(statusReturn),
+segmentObjects(statusReturn)
+{
+    idBlockVector.setDeleter(uprv_deleteUObject);
+    curData = nullptr;
+    compoundFilter = nullptr;
+    parseData = nullptr;
+    variableNames.setValueDeleter(uprv_deleteUObject);
+}
+
+/**
+ * Destructor.
+ */
+TransliteratorParser::~TransliteratorParser() {
+    while (!dataVector.isEmpty())
+        delete (TransliterationRuleData*)(dataVector.orphanElementAt(0));
+    delete compoundFilter;
+    delete parseData;
+    while (!variablesVector.isEmpty())
+        delete (UnicodeFunctor*)variablesVector.orphanElementAt(0);
+}
+
+void
+TransliteratorParser::parse(const UnicodeString& rules,
+                            UTransDirection transDirection,
+                            UParseError& pe,
+                            UErrorCode& ec) {
+    if (U_SUCCESS(ec)) {
+        parseRules(rules, transDirection, ec);
+        pe = parseError;
+    }
+}
+
+/**
+ * Return the compound filter parsed by parse().  Caller owns result.
+ */ 
+UnicodeSet* TransliteratorParser::orphanCompoundFilter() {
+    UnicodeSet* f = compoundFilter;
+    compoundFilter = nullptr;
+    return f;
+}
+
+//----------------------------------------------------------------------
+// Private implementation
+//----------------------------------------------------------------------
+
+/**
+ * Parse the given string as a sequence of rules, separated by newline
+ * characters ('\n'), and cause this object to implement those rules.  Any
+ * previous rules are discarded.  Typically this method is called exactly
+ * once, during construction.
+ * @exception IllegalArgumentException if there is a syntax error in the
+ * rules
+ */
+void TransliteratorParser::parseRules(const UnicodeString& rule,
+                                      UTransDirection theDirection,
+                                      UErrorCode& status)
+{
+    // Clear error struct
+    uprv_memset(&parseError, 0, sizeof(parseError));
+    parseError.line = parseError.offset = -1;
+
+    UBool parsingIDs = true;
+    int32_t ruleCount = 0;
+    
+    while (!dataVector.isEmpty()) {
+        delete (TransliterationRuleData*)(dataVector.orphanElementAt(0));
+    }
+    if (U_FAILURE(status)) {
+        return;
+    }
+
+    idBlockVector.removeAllElements();
+    curData = nullptr;
+    direction = theDirection;
+    ruleCount = 0;
+
+    delete compoundFilter;
+    compoundFilter = nullptr;
+
+    while (!variablesVector.isEmpty()) {
+        delete (UnicodeFunctor*)variablesVector.orphanElementAt(0);
+    }
+    variableNames.removeAll();
+    parseData = new ParseData(0, &variablesVector, &variableNames);
+    if (parseData == nullptr) {
+        status = U_MEMORY_ALLOCATION_ERROR;
+        return;
+    }
+
+    dotStandIn = (char16_t) -1;
+
+    UnicodeString *tempstr = nullptr; // used for memory allocation error checking
+    UnicodeString str; // scratch
+    UnicodeString idBlockResult;
+    int32_t pos = 0;
+    int32_t limit = rule.length();
+
+    // The compound filter offset is an index into idBlockResult.
+    // If it is 0, then the compound filter occurred at the start,
+    // and it is the offset to the _start_ of the compound filter
+    // pattern.  Otherwise it is the offset to the _limit_ of the
+    // compound filter pattern within idBlockResult.
+    compoundFilter = nullptr;
+    int32_t compoundFilterOffset = -1;
+
+    while (pos < limit && U_SUCCESS(status)) {
+        char16_t c = rule.charAt(pos++);
+        if (PatternProps::isWhiteSpace(c)) {
+            // Ignore leading whitespace.
+            continue;
+        }
+        // Skip lines starting with the comment character
+        if (c == RULE_COMMENT_CHAR) {
+            pos = rule.indexOf((char16_t)0x000A /*\n*/, pos) + 1;
+            if (pos == 0) {
+                break; // No "\n" found; rest of rule is a comment
+            }
+            continue; // Either fall out or restart with next line
+        }
+
+        // skip empty rules
+        if (c == END_OF_RULE)
+            continue;
+
+        // keep track of how many rules we've seen
+        ++ruleCount;
+        
+        // We've found the start of a rule or ID.  c is its first
+        // character, and pos points past c.
+        --pos;
+        // Look for an ID token.  Must have at least ID_TOKEN_LEN + 1
+        // chars left.
+        if ((pos + ID_TOKEN_LEN + 1) <= limit &&
+                rule.compare(pos, ID_TOKEN_LEN, ID_TOKEN) == 0) {
+            pos += ID_TOKEN_LEN;
+            c = rule.charAt(pos);
+            while (PatternProps::isWhiteSpace(c) && pos < limit) {
+                ++pos;
+                c = rule.charAt(pos);
+            }
+
+            int32_t p = pos;
+            
+            if (!parsingIDs) {
+                if (curData != nullptr) {
+                    U_ASSERT(!dataVector.hasDeleter());
+                    if (direction == UTRANS_FORWARD)
+                        dataVector.addElement(curData, status);
+                    else
+                        dataVector.insertElementAt(curData, 0, status);
+                    if (U_FAILURE(status)) {
+                        delete curData;
+                    }
+                    curData = nullptr;
+                }
+                parsingIDs = true;
+            }
+
+            TransliteratorIDParser::SingleID* id =
+                TransliteratorIDParser::parseSingleID(rule, p, direction, status);
+            if (p != pos && ICU_Utility::parseChar(rule, p, END_OF_RULE)) {
+                // Successful ::ID parse.
+
+                if (direction == UTRANS_FORWARD) {
+                    idBlockResult.append(id->canonID).append(END_OF_RULE);
+                } else {
+                    idBlockResult.insert(0, END_OF_RULE);
+                    idBlockResult.insert(0, id->canonID);
+                }
+
+            } else {
+                // Couldn't parse an ID.  Try to parse a global filter
+                int32_t withParens = -1;
+                UnicodeSet* f = TransliteratorIDParser::parseGlobalFilter(rule, p, direction, withParens, nullptr);
+                if (f != nullptr) {
+                    if (ICU_Utility::parseChar(rule, p, END_OF_RULE)
+                        && (direction == UTRANS_FORWARD) == (withParens == 0))
+                    {
+                        if (compoundFilter != nullptr) {
+                            // Multiple compound filters
+                            syntaxError(U_MULTIPLE_COMPOUND_FILTERS, rule, pos, status);
+                            delete f;
+                        } else {
+                            compoundFilter = f;
+                            compoundFilterOffset = ruleCount;
+                        }
+                    } else {
+                        delete f;
+                    }
+                } else {
+                    // Invalid ::id
+                    // Can be parsed as neither an ID nor a global filter
+                    syntaxError(U_INVALID_ID, rule, pos, status);
+                }
+            }
+            delete id;
+            pos = p;
+        } else {
+            if (parsingIDs) {
+                tempstr = new UnicodeString(idBlockResult);
+                // nullptr pointer check
+                if (tempstr == nullptr) {
+                    status = U_MEMORY_ALLOCATION_ERROR;
+                    return;
+                }
+                U_ASSERT(idBlockVector.hasDeleter());
+                if (direction == UTRANS_FORWARD)
+                    idBlockVector.adoptElement(tempstr, status);
+                else
+                    idBlockVector.insertElementAt(tempstr, 0, status);
+                if (U_FAILURE(status)) {
+                    return;
+                }
+                idBlockResult.remove();
+                parsingIDs = false;
+                curData = new TransliterationRuleData(status);
+                // nullptr pointer check
+                if (curData == nullptr) {
+                    status = U_MEMORY_ALLOCATION_ERROR;
+                    return;
+                }
+                parseData->data = curData;
+
+                // By default, rules use part of the private use area
+                // E000..F8FF for variables and other stand-ins.  Currently
+                // the range F000..F8FF is typically sufficient.  The 'use
+                // variable range' pragma allows rule sets to modify this.
+                setVariableRange(0xF000, 0xF8FF, status);
+            }
+
+            if (resemblesPragma(rule, pos, limit)) {
+                int32_t ppp = parsePragma(rule, pos, limit, status);
+                if (ppp < 0) {
+                    syntaxError(U_MALFORMED_PRAGMA, rule, pos, status);
+                }
+                pos = ppp;
+            // Parse a rule
+            } else {
+                pos = parseRule(rule, pos, limit, status);
+            }
+        }
+    }
+
+    if (parsingIDs && idBlockResult.length() > 0) {
+        tempstr = new UnicodeString(idBlockResult);
+        // nullptr pointer check
+        if (tempstr == nullptr) {
+            // TODO: Testing, forcing this path, shows many memory leaks. ICU-21701
+            //       intltest translit/TransliteratorTest/TestInstantiation
+            status = U_MEMORY_ALLOCATION_ERROR;
+            return;
+        }
+        if (direction == UTRANS_FORWARD)
+            idBlockVector.adoptElement(tempstr, status);
+        else
+            idBlockVector.insertElementAt(tempstr, 0, status);
+        if (U_FAILURE(status)) {
+            return;
+        }
+    }
+    else if (!parsingIDs && curData != nullptr) {
+        if (direction == UTRANS_FORWARD) {
+            dataVector.addElement(curData, status);
+        } else {
+            dataVector.insertElementAt(curData, 0, status);
+        }
+        if (U_FAILURE(status)) {
+            delete curData;
+            curData = nullptr;
+        }
+    }
+    
+    if (U_SUCCESS(status)) {
+        // Convert the set vector to an array
+        int32_t i, dataVectorSize = dataVector.size();
+        for (i = 0; i < dataVectorSize; i++) {
+            TransliterationRuleData* data = (TransliterationRuleData*)dataVector.elementAt(i);
+            data->variablesLength = variablesVector.size();
+            if (data->variablesLength == 0) {
+                data->variables = 0;
+            } else {
+                data->variables = (UnicodeFunctor**)uprv_malloc(data->variablesLength * sizeof(UnicodeFunctor*));
+                // nullptr pointer check
+                if (data->variables == nullptr) {
+                    status = U_MEMORY_ALLOCATION_ERROR;
+                    return;
+                }
+                data->variablesAreOwned = (i == 0);
+            }
+
+            for (int32_t j = 0; j < data->variablesLength; j++) {
+                data->variables[j] =
+                    static_cast<UnicodeFunctor *>(variablesVector.elementAt(j));
+            }
+            
+            data->variableNames.removeAll();
+            int32_t p = UHASH_FIRST;
+            const UHashElement* he = variableNames.nextElement(p);
+            while (he != nullptr) {
+                UnicodeString* tempus = ((UnicodeString*)(he->value.pointer))->clone();
+                if (tempus == nullptr) {
+                    status = U_MEMORY_ALLOCATION_ERROR;
+                    return;
+                }
+                data->variableNames.put(*((UnicodeString*)(he->key.pointer)),
+                    tempus, status);
+                he = variableNames.nextElement(p);
+            }
+        }
+        variablesVector.removeAllElements();   // keeps them from getting deleted when we succeed
+
+        // Index the rules
+        if (compoundFilter != nullptr) {
+            if ((direction == UTRANS_FORWARD && compoundFilterOffset != 1) ||
+                (direction == UTRANS_REVERSE && compoundFilterOffset != ruleCount)) {
+                status = U_MISPLACED_COMPOUND_FILTER;
+            }
+        }        
+
+        for (i = 0; i < dataVectorSize; i++) {
+            TransliterationRuleData* data = (TransliterationRuleData*)dataVector.elementAt(i);
+            data->ruleSet.freeze(parseError, status);
+        }
+        if (idBlockVector.size() == 1 && ((UnicodeString*)idBlockVector.elementAt(0))->isEmpty()) {
+            idBlockVector.removeElementAt(0);
+        }
+    }
+}
+
+/**
+ * Set the variable range to [start, end] (inclusive).
+ */
+void TransliteratorParser::setVariableRange(int32_t start, int32_t end, UErrorCode& status) {
+    if (start > end || start < 0 || end > 0xFFFF) {
+        status = U_MALFORMED_PRAGMA;
+        return;
+    }
+    
+    curData->variablesBase = (char16_t) start;
+    if (dataVector.size() == 0) {
+        variableNext = (char16_t) start;
+        variableLimit = (char16_t) (end + 1);
+    }
+}
+
+/**
+ * Assert that the given character is NOT within the variable range.
+ * If it is, return false.  This is necessary to ensure that the
+ * variable range does not overlap characters used in a rule.
+ */
+UBool TransliteratorParser::checkVariableRange(UChar32 ch) const {
+    return !(ch >= curData->variablesBase && ch < variableLimit);
+}
+
+/**
+ * Set the maximum backup to 'backup', in response to a pragma
+ * statement.
+ */
+void TransliteratorParser::pragmaMaximumBackup(int32_t /*backup*/) {
+    //TODO Finish
+}
+
+/**
+ * Begin normalizing all rules using the given mode, in response
+ * to a pragma statement.
+ */
+void TransliteratorParser::pragmaNormalizeRules(UNormalizationMode /*mode*/) {
+    //TODO Finish
+}
+
+static const char16_t PRAGMA_USE[] = {0x75,0x73,0x65,0x20,0}; // "use "
+
+static const char16_t PRAGMA_VARIABLE_RANGE[] = {0x7E,0x76,0x61,0x72,0x69,0x61,0x62,0x6C,0x65,0x20,0x72,0x61,0x6E,0x67,0x65,0x20,0x23,0x20,0x23,0x7E,0x3B,0}; // "~variable range # #~;"
+
+static const char16_t PRAGMA_MAXIMUM_BACKUP[] = {0x7E,0x6D,0x61,0x78,0x69,0x6D,0x75,0x6D,0x20,0x62,0x61,0x63,0x6B,0x75,0x70,0x20,0x23,0x7E,0x3B,0}; // "~maximum backup #~;"
+
+static const char16_t PRAGMA_NFD_RULES[] = {0x7E,0x6E,0x66,0x64,0x20,0x72,0x75,0x6C,0x65,0x73,0x7E,0x3B,0}; // "~nfd rules~;"
+
+static const char16_t PRAGMA_NFC_RULES[] = {0x7E,0x6E,0x66,0x63,0x20,0x72,0x75,0x6C,0x65,0x73,0x7E,0x3B,0}; // "~nfc rules~;"
+
+/**
+ * Return true if the given rule looks like a pragma.
+ * @param pos offset to the first non-whitespace character
+ * of the rule.
+ * @param limit pointer past the last character of the rule.
+ */
+UBool TransliteratorParser::resemblesPragma(const UnicodeString& rule, int32_t pos, int32_t limit) {
+    // Must start with /use\s/i
+    return ICU_Utility::parsePattern(rule, pos, limit, UnicodeString(true, PRAGMA_USE, 4), nullptr) >= 0;
+}
+
+/**
+ * Parse a pragma.  This method assumes resemblesPragma() has
+ * already returned true.
+ * @param pos offset to the first non-whitespace character
+ * of the rule.
+ * @param limit pointer past the last character of the rule.
+ * @return the position index after the final ';' of the pragma,
+ * or -1 on failure.
+ */
+int32_t TransliteratorParser::parsePragma(const UnicodeString& rule, int32_t pos, int32_t limit, UErrorCode& status) {
+    int32_t array[2];
+    
+    // resemblesPragma() has already returned true, so we
+    // know that pos points to /use\s/i; we can skip 4 characters
+    // immediately
+    pos += 4;
+    
+    // Here are the pragmas we recognize:
+    // use variable range 0xE000 0xEFFF;
+    // use maximum backup 16;
+    // use nfd rules;
+    // use nfc rules;
+    int p = ICU_Utility::parsePattern(rule, pos, limit, UnicodeString(true, PRAGMA_VARIABLE_RANGE, -1), array);
+    if (p >= 0) {
+        setVariableRange(array[0], array[1], status);
+        return p;
+    }
+    
+    p = ICU_Utility::parsePattern(rule, pos, limit, UnicodeString(true, PRAGMA_MAXIMUM_BACKUP, -1), array);
+    if (p >= 0) {
+        pragmaMaximumBackup(array[0]);
+        return p;
+    }
+    
+    p = ICU_Utility::parsePattern(rule, pos, limit, UnicodeString(true, PRAGMA_NFD_RULES, -1), nullptr);
+    if (p >= 0) {
+        pragmaNormalizeRules(UNORM_NFD);
+        return p;
+    }
+    
+    p = ICU_Utility::parsePattern(rule, pos, limit, UnicodeString(true, PRAGMA_NFC_RULES, -1), nullptr);
+    if (p >= 0) {
+        pragmaNormalizeRules(UNORM_NFC);
+        return p;
+    }
+    
+    // Syntax error: unable to parse pragma
+    return -1;
+}
+
+/**
+ * MAIN PARSER.  Parse the next rule in the given rule string, starting
+ * at pos.  Return the index after the last character parsed.  Do not
+ * parse characters at or after limit.
+ *
+ * Important:  The character at pos must be a non-whitespace character
+ * that is not the comment character.
+ *
+ * This method handles quoting, escaping, and whitespace removal.  It
+ * parses the end-of-rule character.  It recognizes context and cursor
+ * indicators.  Once it does a lexical breakdown of the rule at pos, it
+ * creates a rule object and adds it to our rule list.
+ */
+int32_t TransliteratorParser::parseRule(const UnicodeString& rule, int32_t pos, int32_t limit, UErrorCode& status) {
+    // Locate the left side, operator, and right side
+    int32_t start = pos;
+    char16_t op = 0;
+    int32_t i;
+
+    // Set up segments data
+    segmentStandins.truncate(0);
+    segmentObjects.removeAllElements();
+
+    // Use pointers to automatics to make swapping possible.
+    RuleHalf _left(*this), _right(*this);
+    RuleHalf* left = &_left;
+    RuleHalf* right = &_right;
+
+    undefinedVariableName.remove();
+    pos = left->parse(rule, pos, limit, status);
+    if (U_FAILURE(status)) {
+        return start;
+    }
+
+    if (pos == limit || u_strchr(gOPERATORS, (op = rule.charAt(--pos))) == nullptr) {
+        return syntaxError(U_MISSING_OPERATOR, rule, start, status);
+    }
+    ++pos;
+
+    // Found an operator char.  Check for forward-reverse operator.
+    if (op == REVERSE_RULE_OP &&
+        (pos < limit && rule.charAt(pos) == FORWARD_RULE_OP)) {
+        ++pos;
+        op = FWDREV_RULE_OP;
+    }
+
+    // Translate alternate op characters.
+    switch (op) {
+    case ALT_FORWARD_RULE_OP:
+        op = FORWARD_RULE_OP;
+        break;
+    case ALT_REVERSE_RULE_OP:
+        op = REVERSE_RULE_OP;
+        break;
+    case ALT_FWDREV_RULE_OP:
+        op = FWDREV_RULE_OP;
+        break;
+    }
+
+    pos = right->parse(rule, pos, limit, status);
+    if (U_FAILURE(status)) {
+        return start;
+    }
+
+    if (pos < limit) {
+        if (rule.charAt(--pos) == END_OF_RULE) {
+            ++pos;
+        } else {
+            // RuleHalf parser must have terminated at an operator
+            return syntaxError(U_UNQUOTED_SPECIAL, rule, start, status);
+        }
+    }
+
+    if (op == VARIABLE_DEF_OP) {
+        // LHS is the name.  RHS is a single character, either a literal
+        // or a set (already parsed).  If RHS is longer than one
+        // character, it is either a multi-character string, or multiple
+        // sets, or a mixture of chars and sets -- syntax error.
+
+        // We expect to see a single undefined variable (the one being
+        // defined).
+        if (undefinedVariableName.length() == 0) {
+            // "Missing '$' or duplicate definition"
+            return syntaxError(U_BAD_VARIABLE_DEFINITION, rule, start, status);
+        }
+        if (left->text.length() != 1 || left->text.charAt(0) != variableLimit) {
+            // "Malformed LHS"
+            return syntaxError(U_MALFORMED_VARIABLE_DEFINITION, rule, start, status);
+        }
+        if (left->anchorStart || left->anchorEnd ||
+            right->anchorStart || right->anchorEnd) {
+            return syntaxError(U_MALFORMED_VARIABLE_DEFINITION, rule, start, status);
+        } 
+        // We allow anything on the right, including an empty string.
+        UnicodeString* value = new UnicodeString(right->text);
+        // nullptr pointer check
+        if (value == nullptr) {
+            return syntaxError(U_MEMORY_ALLOCATION_ERROR, rule, start, status);
+        }
+        variableNames.put(undefinedVariableName, value, status);
+        ++variableLimit;
+        return pos;
+    }
+
+    // If this is not a variable definition rule, we shouldn't have
+    // any undefined variable names.
+    if (undefinedVariableName.length() != 0) {
+        return syntaxError(// "Undefined variable $" + undefinedVariableName,
+                    U_UNDEFINED_VARIABLE,
+                    rule, start, status);
+    }
+
+    // Verify segments
+    if (segmentStandins.length() > segmentObjects.size()) {
+        syntaxError(U_UNDEFINED_SEGMENT_REFERENCE, rule, start, status);
+    }
+    for (i=0; i<segmentStandins.length(); ++i) {
+        if (segmentStandins.charAt(i) == 0) {
+            syntaxError(U_INTERNAL_TRANSLITERATOR_ERROR, rule, start, status); // will never happen
+        }
+    }
+    for (i=0; i<segmentObjects.size(); ++i) {
+        if (segmentObjects.elementAt(i) == nullptr) {
+            syntaxError(U_INTERNAL_TRANSLITERATOR_ERROR, rule, start, status); // will never happen
+        }
+    }
+    
+    // If the direction we want doesn't match the rule
+    // direction, do nothing.
+    if (op != FWDREV_RULE_OP &&
+        ((direction == UTRANS_FORWARD) != (op == FORWARD_RULE_OP))) {
+        return pos;
+    }
+
+    // Transform the rule into a forward rule by swapping the
+    // sides if necessary.
+    if (direction == UTRANS_REVERSE) {
+        left = &_right;
+        right = &_left;
+    }
+
+    // Remove non-applicable elements in forward-reverse
+    // rules.  Bidirectional rules ignore elements that do not
+    // apply.
+    if (op == FWDREV_RULE_OP) {
+        right->removeContext();
+        left->cursor = -1;
+        left->cursorOffset = 0;
+    }
+
+    // Normalize context
+    if (left->ante < 0) {
+        left->ante = 0;
+    }
+    if (left->post < 0) {
+        left->post = left->text.length();
+    }
+
+    // Context is only allowed on the input side.  Cursors are only
+    // allowed on the output side.  Segment delimiters can only appear
+    // on the left, and references on the right.  Cursor offset
+    // cannot appear without an explicit cursor.  Cursor offset
+    // cannot place the cursor outside the limits of the context.
+    // Anchors are only allowed on the input side.
+    if (right->ante >= 0 || right->post >= 0 || left->cursor >= 0 ||
+        (right->cursorOffset != 0 && right->cursor < 0) ||
+        // - The following two checks were used to ensure that the
+        // - the cursor offset stayed within the ante- or postcontext.
+        // - However, with the addition of quantifiers, we have to
+        // - allow arbitrary cursor offsets and do runtime checking.
+        //(right->cursorOffset > (left->text.length() - left->post)) ||
+        //(-right->cursorOffset > left->ante) ||
+        right->anchorStart || right->anchorEnd ||
+        !left->isValidInput(*this) || !right->isValidOutput(*this) ||
+        left->ante > left->post) {
+
+        return syntaxError(U_MALFORMED_RULE, rule, start, status);
+    }
+
+    // Flatten segment objects vector to an array
+    UnicodeFunctor** segmentsArray = nullptr;
+    if (segmentObjects.size() > 0) {
+        segmentsArray = (UnicodeFunctor **)uprv_malloc(segmentObjects.size() * sizeof(UnicodeFunctor *));
+        // Null pointer check
+        if (segmentsArray == nullptr) {
+            return syntaxError(U_MEMORY_ALLOCATION_ERROR, rule, start, status);
+        }
+        segmentObjects.toArray((void**) segmentsArray);
+    }
+    TransliterationRule* temptr = new TransliterationRule(
+            left->text, left->ante, left->post,
+            right->text, right->cursor, right->cursorOffset,
+            segmentsArray,
+            segmentObjects.size(),
+            left->anchorStart, left->anchorEnd,
+            curData,
+            status);
+    //Null pointer check
+    if (temptr == nullptr) {
+        uprv_free(segmentsArray);
+        return syntaxError(U_MEMORY_ALLOCATION_ERROR, rule, start, status);
+    }
+
+    curData->ruleSet.addRule(temptr, status);
+
+    return pos;
+}
+
+/**
+ * Called by main parser upon syntax error.  Search the rule string
+ * for the probable end of the rule.  Of course, if the error is that
+ * the end of rule marker is missing, then the rule end will not be found.
+ * In any case the rule start will be correctly reported.
+ * @param msg error description
+ * @param rule pattern string
+ * @param start position of first character of current rule
+ */
+int32_t TransliteratorParser::syntaxError(UErrorCode parseErrorCode,
+                                          const UnicodeString& rule,
+                                          int32_t pos,
+                                          UErrorCode& status)
+{
+    parseError.offset = pos;
+    parseError.line = 0 ; /* we are not using line numbers */
+    
+    // for pre-context
+    const int32_t LEN = U_PARSE_CONTEXT_LEN - 1;
+    int32_t start = uprv_max(pos - LEN, 0);
+    int32_t stop  = pos;
+    
+    rule.extract(start,stop-start,parseError.preContext);
+    //null terminate the buffer
+    parseError.preContext[stop-start] = 0;
+    
+    //for post-context
+    start = pos;
+    stop  = uprv_min(pos + LEN, rule.length());
+    
+    rule.extract(start,stop-start,parseError.postContext);
+    //null terminate the buffer
+    parseError.postContext[stop-start]= 0;
+
+    status = (UErrorCode)parseErrorCode;
+    return pos;
+
+}
+
+/**
+ * Parse a UnicodeSet out, store it, and return the stand-in character
+ * used to represent it.
+ */
+char16_t TransliteratorParser::parseSet(const UnicodeString& rule,
+                                          ParsePosition& pos,
+                                          UErrorCode& status) {
+    UnicodeSet* set = new UnicodeSet(rule, pos, USET_IGNORE_SPACE, parseData, status);
+    // Null pointer check
+    if (set == nullptr) {
+        status = U_MEMORY_ALLOCATION_ERROR;
+        return (char16_t)0x0000; // Return empty character with error.
+    }
+    set->compact();
+    return generateStandInFor(set, status);
+}
+
+/**
+ * Generate and return a stand-in for a new UnicodeFunctor.  Store
+ * the matcher (adopt it).
+ */
+char16_t TransliteratorParser::generateStandInFor(UnicodeFunctor* adopted, UErrorCode& status) {
+    // assert(obj != null);
+    
+    // Look up previous stand-in, if any.  This is a short list
+    // (typical n is 0, 1, or 2); linear search is optimal.
+    for (int32_t i=0; i<variablesVector.size(); ++i) {
+        if (variablesVector.elementAt(i) == adopted) { // [sic] pointer comparison
+            return (char16_t) (curData->variablesBase + i);
+        }
+    }
+    
+    if (variableNext >= variableLimit) {
+        delete adopted;
+        status = U_VARIABLE_RANGE_EXHAUSTED;
+        return 0;
+    }
+    variablesVector.addElement(adopted, status);
+    if (U_FAILURE(status)) {
+        delete adopted;
+        return 0;
+    }
+    return variableNext++;
+}
+
+/**
+ * Return the standin for segment seg (1-based).
+ */
+char16_t TransliteratorParser::getSegmentStandin(int32_t seg, UErrorCode& status) {
+    // Special character used to indicate an empty spot
+    char16_t empty = curData->variablesBase - 1;
+    while (segmentStandins.length() < seg) {
+        segmentStandins.append(empty);
+    }
+    char16_t c = segmentStandins.charAt(seg-1);
+    if (c == empty) {
+        if (variableNext >= variableLimit) {
+            status = U_VARIABLE_RANGE_EXHAUSTED;
+            return 0;
+        }
+        c = variableNext++;
+        // Set a placeholder in the primary variables vector that will be
+        // filled in later by setSegmentObject().  We know that we will get
+        // called first because setSegmentObject() will call us.
+        variablesVector.addElement((void*) nullptr, status);
+        segmentStandins.setCharAt(seg-1, c);
+    }
+    return c;
+}
+
+/**
+ * Set the object for segment seg (1-based).
+ */
+void TransliteratorParser::setSegmentObject(int32_t seg, StringMatcher* adopted, UErrorCode& status) {
+    // Since we call parseSection() recursively, nested
+    // segments will result in segment i+1 getting parsed
+    // and stored before segment i; be careful with the
+    // vector handling here.
+    if (segmentObjects.size() < seg) {
+        segmentObjects.setSize(seg, status);
+    }
+    if (U_FAILURE(status)) {
+        return;
+    }
+    int32_t index = getSegmentStandin(seg, status) - curData->variablesBase;
+    if (segmentObjects.elementAt(seg-1) != nullptr ||
+        variablesVector.elementAt(index) != nullptr) {
+        // should never happen
+        if (U_SUCCESS(status)) {status = U_INTERNAL_TRANSLITERATOR_ERROR;}
+        return;
+    }
+    // Note: neither segmentObjects or variablesVector has an object deleter function.
+    segmentObjects.setElementAt(adopted, seg-1);
+    variablesVector.setElementAt(adopted, index);
+}
+
+/**
+ * Return the stand-in for the dot set.  It is allocated the first
+ * time and reused thereafter.
+ */
+char16_t TransliteratorParser::getDotStandIn(UErrorCode& status) {
+    if (dotStandIn == (char16_t) -1) {
+        UnicodeSet* tempus = new UnicodeSet(UnicodeString(true, DOT_SET, -1), status);
+        // Null pointer check.
+        if (tempus == nullptr) {
+            status = U_MEMORY_ALLOCATION_ERROR;
+            return (char16_t)0x0000;
+        }
+        dotStandIn = generateStandInFor(tempus, status);
+    }
+    return dotStandIn;
+}
+
+/**
+ * Append the value of the given variable name to the given
+ * UnicodeString.
+ */
+void TransliteratorParser::appendVariableDef(const UnicodeString& name,
+                                                  UnicodeString& buf,
+                                                  UErrorCode& status) {
+    const UnicodeString* s = (const UnicodeString*) variableNames.get(name);
+    if (s == nullptr) {
+        // We allow one undefined variable so that variable definition
+        // statements work.  For the first undefined variable we return
+        // the special placeholder variableLimit-1, and save the variable
+        // name.
+        if (undefinedVariableName.length() == 0) {
+            undefinedVariableName = name;
+            if (variableNext >= variableLimit) {
+                // throw new RuntimeException("Private use variables exhausted");
+                status = U_ILLEGAL_ARGUMENT_ERROR;
+                return;
+            }
+            buf.append((char16_t) --variableLimit);
+        } else {
+            //throw new IllegalArgumentException("Undefined variable $"
+            //                                   + name);
+            status = U_ILLEGAL_ARGUMENT_ERROR;
+            return;
+        }
+    } else {
+        buf.append(*s);
+    }
+}
+
+/**
+ * Glue method to get around access restrictions in C++.
+ */
+/*Transliterator* TransliteratorParser::createBasicInstance(const UnicodeString& id, const UnicodeString* canonID) {
+    return Transliterator::createBasicInstance(id, canonID);
+}*/
+
+U_NAMESPACE_END
+
+U_CAPI int32_t
+utrans_stripRules(const char16_t *source, int32_t sourceLen, char16_t *target, UErrorCode *status) {
+    U_NAMESPACE_USE
+
+    //const char16_t *sourceStart = source;
+    const char16_t *targetStart = target;
+    const char16_t *sourceLimit = source+sourceLen;
+    char16_t *targetLimit = target+sourceLen;
+    UChar32 c = 0;
+    UBool quoted = false;
+    int32_t index;
+
+    uprv_memset(target, 0, sourceLen*U_SIZEOF_UCHAR);
+
+    /* read the rules into the buffer */
+    while (source < sourceLimit)
+    {
+        index=0;
+        U16_NEXT_UNSAFE(source, index, c);
+        source+=index;
+        if(c == QUOTE) {
+            quoted = (UBool)!quoted;
+        }
+        else if (!quoted) {
+            if (c == RULE_COMMENT_CHAR) {
+                /* skip comments and all preceding spaces */
+                while (targetStart < target && *(target - 1) == 0x0020) {
+                    target--;
+                }
+                do {
+                    if (source == sourceLimit) {
+                        c = U_SENTINEL;
+                        break;
+                    }
+                    c = *(source++);
+                }
+                while (c != CR && c != LF);
+                if (c < 0) {
+                    break;
+                }
+            }
+            else if (c == ESCAPE && source < sourceLimit) {
+                UChar32   c2 = *source;
+                if (c2 == CR || c2 == LF) {
+                    /* A backslash at the end of a line. */
+                    /* Since we're stripping lines, ignore the backslash. */
+                    source++;
+                    continue;
+                }
+                if (c2 == 0x0075 && source+5 < sourceLimit) { /* \u seen. \U isn't unescaped. */
+                    int32_t escapeOffset = 0;
+                    UnicodeString escapedStr(source, 5);
+                    c2 = escapedStr.unescapeAt(escapeOffset);
+
+                    if (c2 == (UChar32)0xFFFFFFFF || escapeOffset == 0)
+                    {
+                        *status = U_PARSE_ERROR;
+                        return 0;
+                    }
+                    if (!PatternProps::isWhiteSpace(c2) && !u_iscntrl(c2) && !u_ispunct(c2)) {
+                        /* It was escaped for a reason. Write what it was suppose to be. */
+                        source+=5;
+                        c = c2;
+                    }
+                }
+                else if (c2 == QUOTE) {
+                    /* \' seen. Make sure we don't do anything when we see it again. */
+                    quoted = (UBool)!quoted;
+                }
+            }
+        }
+        if (c == CR || c == LF)
+        {
+            /* ignore spaces carriage returns, and all leading spaces on the next line.
+            * and line feed unless in the form \uXXXX
+            */
+            quoted = false;
+            while (source < sourceLimit) {
+                c = *(source);
+                if (c != CR && c != LF && c != 0x0020) {
+                    break;
+                }
+                source++;
+            }
+            continue;
+        }
+
+        /* Append char16_t * after dissembling if c > 0xffff*/
+        index=0;
+        U16_APPEND_UNSAFE(target, index, c);
+        target+=index;
+    }
+    if (target < targetLimit) {
+        *target = 0;
+    }
+    return (int32_t)(target-targetStart);
+}
+
+#endif /* #if !UCONFIG_NO_TRANSLITERATION */