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diff --git a/src/include/fe_utils/psqlscan_int.h b/src/include/fe_utils/psqlscan_int.h
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+/*-------------------------------------------------------------------------
+ *
+ * psqlscan_int.h
+ *	  lexical scanner internal declarations
+ *
+ * This file declares the PsqlScanStateData structure used by psqlscan.l
+ * and shared by other lexers compatible with it, such as psqlscanslash.l.
+ *
+ * One difficult aspect of this code is that we need to work in multibyte
+ * encodings that are not ASCII-safe.  A "safe" encoding is one in which each
+ * byte of a multibyte character has the high bit set (it's >= 0x80).  Since
+ * all our lexing rules treat all high-bit-set characters alike, we don't
+ * really need to care whether such a byte is part of a sequence or not.
+ * In an "unsafe" encoding, we still expect the first byte of a multibyte
+ * sequence to be >= 0x80, but later bytes might not be.  If we scan such
+ * a sequence as-is, the lexing rules could easily be fooled into matching
+ * such bytes to ordinary ASCII characters.  Our solution for this is to
+ * substitute 0xFF for each non-first byte within the data presented to flex.
+ * The flex rules will then pass the FF's through unmolested.  The
+ * psqlscan_emit() subroutine is responsible for looking back to the original
+ * string and replacing FF's with the corresponding original bytes.
+ *
+ * Another interesting thing we do here is scan different parts of the same
+ * input with physically separate flex lexers (ie, lexers written in separate
+ * .l files).  We can get away with this because the only part of the
+ * persistent state of a flex lexer that depends on its parsing rule tables
+ * is the start state number, which is easy enough to manage --- usually,
+ * in fact, we just need to set it to INITIAL when changing lexers.  But to
+ * make that work at all, we must use re-entrant lexers, so that all the
+ * relevant state is in the yyscan_t attached to the PsqlScanState;
+ * if we were using lexers with separate static state we would soon end up
+ * with dangling buffer pointers in one or the other.  Also note that this
+ * is unlikely to work very nicely if the lexers aren't all built with the
+ * same flex version, or if they don't use the same flex options.
+ *
+ *
+ * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/fe_utils/psqlscan_int.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef PSQLSCAN_INT_H
+#define PSQLSCAN_INT_H
+
+#include "fe_utils/psqlscan.h"
+
+/*
+ * These are just to allow this file to be compilable standalone for header
+ * validity checking; in actual use, this file should always be included
+ * from the body of a flex file, where these symbols are already defined.
+ */
+#ifndef YY_TYPEDEF_YY_BUFFER_STATE
+#define YY_TYPEDEF_YY_BUFFER_STATE
+typedef struct yy_buffer_state *YY_BUFFER_STATE;
+#endif
+#ifndef YY_TYPEDEF_YY_SCANNER_T
+#define YY_TYPEDEF_YY_SCANNER_T
+typedef void *yyscan_t;
+#endif
+
+/*
+ * We use a stack of flex buffers to handle substitution of psql variables.
+ * Each stacked buffer contains the as-yet-unread text from one psql variable.
+ * When we pop the stack all the way, we resume reading from the outer buffer
+ * identified by scanbufhandle.
+ */
+typedef struct StackElem
+{
+	YY_BUFFER_STATE buf;		/* flex input control structure */
+	char	   *bufstring;		/* data actually being scanned by flex */
+	char	   *origstring;		/* copy of original data, if needed */
+	char	   *varname;		/* name of variable providing data, or NULL */
+	struct StackElem *next;
+} StackElem;
+
+/*
+ * All working state of the lexer must be stored in PsqlScanStateData
+ * between calls.  This allows us to have multiple open lexer operations,
+ * which is needed for nested include files.  The lexer itself is not
+ * recursive, but it must be re-entrant.
+ */
+typedef struct PsqlScanStateData
+{
+	yyscan_t	scanner;		/* Flex's state for this PsqlScanState */
+
+	PQExpBuffer output_buf;		/* current output buffer */
+
+	StackElem  *buffer_stack;	/* stack of variable expansion buffers */
+
+	/*
+	 * These variables always refer to the outer buffer, never to any stacked
+	 * variable-expansion buffer.
+	 */
+	YY_BUFFER_STATE scanbufhandle;
+	char	   *scanbuf;		/* start of outer-level input buffer */
+	const char *scanline;		/* current input line at outer level */
+
+	/* safe_encoding, curline, refline are used by emit() to replace FFs */
+	int			encoding;		/* encoding being used now */
+	bool		safe_encoding;	/* is current encoding "safe"? */
+	bool		std_strings;	/* are string literals standard? */
+	const char *curline;		/* actual flex input string for cur buf */
+	const char *refline;		/* original data for cur buffer */
+
+	/*
+	 * All this state lives across successive input lines, until explicitly
+	 * reset by psql_scan_reset.  start_state is adopted by yylex() on entry,
+	 * and updated with its finishing state on exit.
+	 */
+	int			start_state;	/* yylex's starting/finishing state */
+	int			state_before_str_stop;	/* start cond. before end quote */
+	int			paren_depth;	/* depth of nesting in parentheses */
+	int			xcdepth;		/* depth of nesting in slash-star comments */
+	char	   *dolqstart;		/* current $foo$ quote start string */
+
+	/*
+	 * Callback functions provided by the program making use of the lexer,
+	 * plus a void* callback passthrough argument.
+	 */
+	const PsqlScanCallbacks *callbacks;
+	void	   *cb_passthrough;
+} PsqlScanStateData;
+
+
+/*
+ * Functions exported by psqlscan.l, but only meant for use within
+ * compatible lexers.
+ */
+extern void psqlscan_push_new_buffer(PsqlScanState state,
+									 const char *newstr, const char *varname);
+extern void psqlscan_pop_buffer_stack(PsqlScanState state);
+extern void psqlscan_select_top_buffer(PsqlScanState state);
+extern bool psqlscan_var_is_current_source(PsqlScanState state,
+										   const char *varname);
+extern YY_BUFFER_STATE psqlscan_prepare_buffer(PsqlScanState state,
+											   const char *txt, int len,
+											   char **txtcopy);
+extern void psqlscan_emit(PsqlScanState state, const char *txt, int len);
+extern char *psqlscan_extract_substring(PsqlScanState state,
+										const char *txt, int len);
+extern void psqlscan_escape_variable(PsqlScanState state,
+									 const char *txt, int len,
+									 PsqlScanQuoteType quote);
+extern void psqlscan_test_variable(PsqlScanState state,
+								   const char *txt, int len);
+
+#endif							/* PSQLSCAN_INT_H */