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diff --git a/src/include/parser/scanner.h b/src/include/parser/scanner.h
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+/*-------------------------------------------------------------------------
+ *
+ * scanner.h
+ *		API for the core scanner (flex machine)
+ *
+ * The core scanner is also used by PL/pgSQL, so we provide a public API
+ * for it.  However, the rest of the backend is only expected to use the
+ * higher-level API provided by parser.h.
+ *
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/parser/scanner.h
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#ifndef SCANNER_H
+#define SCANNER_H
+
+#include "common/keywords.h"
+
+/*
+ * The scanner returns extra data about scanned tokens in this union type.
+ * Note that this is a subset of the fields used in YYSTYPE of the bison
+ * parsers built atop the scanner.
+ */
+typedef union core_YYSTYPE
+{
+	int			ival;			/* for integer literals */
+	char	   *str;			/* for identifiers and non-integer literals */
+	const char *keyword;		/* canonical spelling of keywords */
+} core_YYSTYPE;
+
+/*
+ * We track token locations in terms of byte offsets from the start of the
+ * source string, not the column number/line number representation that
+ * bison uses by default.  Also, to minimize overhead we track only one
+ * location (usually the first token location) for each construct, not
+ * the beginning and ending locations as bison does by default.  It's
+ * therefore sufficient to make YYLTYPE an int.
+ */
+#define YYLTYPE  int
+
+/*
+ * Another important component of the scanner's API is the token code numbers.
+ * However, those are not defined in this file, because bison insists on
+ * defining them for itself.  The token codes used by the core scanner are
+ * the ASCII characters plus these:
+ *	%token <str>	IDENT UIDENT FCONST SCONST USCONST BCONST XCONST Op
+ *	%token <ival>	ICONST PARAM
+ *	%token			TYPECAST DOT_DOT COLON_EQUALS EQUALS_GREATER
+ *	%token			LESS_EQUALS GREATER_EQUALS NOT_EQUALS
+ * The above token definitions *must* be the first ones declared in any
+ * bison parser built atop this scanner, so that they will have consistent
+ * numbers assigned to them (specifically, IDENT = 258 and so on).
+ */
+
+/*
+ * The YY_EXTRA data that a flex scanner allows us to pass around.
+ * Private state needed by the core scanner goes here.  Note that the actual
+ * yy_extra struct may be larger and have this as its first component, thus
+ * allowing the calling parser to keep some fields of its own in YY_EXTRA.
+ */
+typedef struct core_yy_extra_type
+{
+	/*
+	 * The string the scanner is physically scanning.  We keep this mainly so
+	 * that we can cheaply compute the offset of the current token (yytext).
+	 */
+	char	   *scanbuf;
+	Size		scanbuflen;
+
+	/*
+	 * The keyword list to use, and the associated grammar token codes.
+	 */
+	const ScanKeywordList *keywordlist;
+	const uint16 *keyword_tokens;
+
+	/*
+	 * Scanner settings to use.  These are initialized from the corresponding
+	 * GUC variables by scanner_init().  Callers can modify them after
+	 * scanner_init() if they don't want the scanner's behavior to follow the
+	 * prevailing GUC settings.
+	 */
+	int			backslash_quote;
+	bool		escape_string_warning;
+	bool		standard_conforming_strings;
+
+	/*
+	 * literalbuf is used to accumulate literal values when multiple rules are
+	 * needed to parse a single literal.  Call startlit() to reset buffer to
+	 * empty, addlit() to add text.  NOTE: the string in literalbuf is NOT
+	 * necessarily null-terminated, but there always IS room to add a trailing
+	 * null at offset literallen.  We store a null only when we need it.
+	 */
+	char	   *literalbuf;		/* palloc'd expandable buffer */
+	int			literallen;		/* actual current string length */
+	int			literalalloc;	/* current allocated buffer size */
+
+	/*
+	 * Random assorted scanner state.
+	 */
+	int			state_before_str_stop;	/* start cond. before end quote */
+	int			xcdepth;		/* depth of nesting in slash-star comments */
+	char	   *dolqstart;		/* current $foo$ quote start string */
+	YYLTYPE		save_yylloc;	/* one-element stack for PUSH_YYLLOC() */
+
+	/* first part of UTF16 surrogate pair for Unicode escapes */
+	int32		utf16_first_part;
+
+	/* state variables for literal-lexing warnings */
+	bool		warn_on_first_escape;
+	bool		saw_non_ascii;
+} core_yy_extra_type;
+
+/*
+ * The type of yyscanner is opaque outside scan.l.
+ */
+typedef void *core_yyscan_t;
+
+/* Support for scanner_errposition_callback function */
+typedef struct ScannerCallbackState
+{
+	core_yyscan_t yyscanner;
+	int			location;
+	ErrorContextCallback errcallback;
+} ScannerCallbackState;
+
+
+/* Constant data exported from parser/scan.l */
+extern PGDLLIMPORT const uint16 ScanKeywordTokens[];
+
+/* Entry points in parser/scan.l */
+extern core_yyscan_t scanner_init(const char *str,
+								  core_yy_extra_type *yyext,
+								  const ScanKeywordList *keywordlist,
+								  const uint16 *keyword_tokens);
+extern void scanner_finish(core_yyscan_t yyscanner);
+extern int	core_yylex(core_YYSTYPE *lvalp, YYLTYPE *llocp,
+					   core_yyscan_t yyscanner);
+extern int	scanner_errposition(int location, core_yyscan_t yyscanner);
+extern void setup_scanner_errposition_callback(ScannerCallbackState *scbstate,
+											   core_yyscan_t yyscanner,
+											   int location);
+extern void cancel_scanner_errposition_callback(ScannerCallbackState *scbstate);
+extern void scanner_yyerror(const char *message, core_yyscan_t yyscanner) pg_attribute_noreturn();
+
+#endif							/* SCANNER_H */