Fix some cases of indirectly casting away const.

Newest versions of gcc are able to detect cases where code implicitly
casts away const by assigning the result of strchr() or a similar
function applied to a "const char *" value to a target variable
that's just "char *".  This of course creates a hazard of not getting
a compiler warning about scribbling on a string one was not supposed
to, so fixing up such cases is good.

This patch fixes a dozen or so places where we were doing that.
Most are trivial additions of "const" to the target variable,
since no actually-hazardous change was occurring.  There is one
place in ecpg.trailer where we were indeed violating the intention
of not modifying a string passed in as "const char *".  I believe
that's harmless not a live bug, but let's fix it by copying the
string before modifying it.

There is a remaining trouble spot in ecpg/preproc/variable.c,
which requires more complex surgery.  I've left that out of this
commit because I want to study that code a bit more first.

We probably will want to back-patch this once compilers that detect
this pattern get into wider circulation, but for now I'm just
going to apply it to master to see what the buildfarm says.

Thanks to Bertrand Drouvot for finding a couple more spots than
I had.

Author: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Discussion: https://postgr.es/m/1324889.1764886170@sss.pgh.pa.us

src/backend/catalog/pg_type.c

@@ -948,7 +948,7 @@ char *
 makeMultirangeTypeName(const char *rangeTypeName, Oid typeNamespace)
 {
 	char	   *buf;
-	char	   *rangestr;
+	const char *rangestr;
 
 	/*
 	 * If the range type name contains "range" then change that to

src/backend/tsearch/spell.c

@@ -2320,7 +2320,7 @@ CheckCompoundAffixes(CMPDAffix **ptr, const char *word, int len, bool CheckInPla
 	}
 	else
 	{
-		char	   *affbegin;
+		const char *affbegin;
 
 		while ((*ptr)->affix)
 		{

src/backend/utils/adt/formatting.c

@@ -1046,8 +1046,9 @@ typedef struct NUMProc
 	char	   *number,			/* string with number	*/
 			   *number_p,		/* pointer to current number position */
 			   *inout,			/* in / out buffer	*/
-			   *inout_p,		/* pointer to current inout position */
-			   *last_relevant,	/* last relevant number after decimal point */
+			   *inout_p;		/* pointer to current inout position */
+
+	const char *last_relevant,	/* last relevant number after decimal point */
 
 			   *L_negative_sign,	/* Locale */
 			   *L_positive_sign,
@@ -1118,7 +1119,7 @@ static FormatNode *NUM_cache(int len, NUMDesc *Num, const text *pars_str, bool *
 static char *int_to_roman(int number);
 static int	roman_to_int(NUMProc *Np, size_t input_len);
 static void NUM_prepare_locale(NUMProc *Np);
-static char *get_last_relevant_decnum(const char *num);
+static const char *get_last_relevant_decnum(const char *num);
 static void NUM_numpart_from_char(NUMProc *Np, int id, size_t input_len);
 static void NUM_numpart_to_char(NUMProc *Np, int id);
 static char *NUM_processor(FormatNode *node, NUMDesc *Num, char *inout,
@@ -5297,10 +5298,10 @@ NUM_prepare_locale(NUMProc *Np)
  * If there is no decimal point, return NULL (which will result in same
  * behavior as if FM hadn't been specified).
  */
-static char *
+static const char *
 get_last_relevant_decnum(const char *num)
 {
-	char	   *result,
+	const char *result,
 			   *p = strchr(num, '.');
 
 #ifdef DEBUG_TO_FROM_CHAR

src/backend/utils/adt/pg_locale.c

@@ -953,7 +953,7 @@ get_iso_localename(const char *winlocname)
 	wchar_t		wc_locale_name[LOCALE_NAME_MAX_LENGTH];
 	wchar_t		buffer[LOCALE_NAME_MAX_LENGTH];
 	static char iso_lc_messages[LOCALE_NAME_MAX_LENGTH];
-	char	   *period;
+	const char *period;
 	int			len;
 	int			ret_val;
 

src/backend/utils/adt/xid8funcs.c

@@ -194,7 +194,7 @@ is_visible_fxid(FullTransactionId value, const pg_snapshot *snap)
 #ifdef USE_BSEARCH_IF_NXIP_GREATER
 	else if (snap->nxip > USE_BSEARCH_IF_NXIP_GREATER)
 	{
-		void	   *res;
+		const void *res;
 
 		res = bsearch(&value, snap->xip, snap->nxip, sizeof(FullTransactionId),
 					  cmp_fxid);

src/bin/pg_waldump/pg_waldump.c

@@ -160,7 +160,7 @@ create_fullpage_directory(char *path)
 static void
 split_path(const char *path, char **dir, char **fname)
 {
-	char	   *sep;
+	const char *sep;
 
 	/* split filepath into directory & filename */
 	sep = strrchr(path, '/');

src/bin/pgbench/pgbench.c

@@ -6254,7 +6254,7 @@ findBuiltin(const char *name)
 static int
 parseScriptWeight(const char *option, char **script)
 {
-	char	   *sep;
+	const char *sep;
 	int			weight;
 
 	if ((sep = strrchr(option, WSEP)))

src/common/compression.c

@@ -425,7 +425,7 @@ validate_compress_specification(pg_compress_specification *spec)
 void
 parse_compress_options(const char *option, char **algorithm, char **detail)
 {
-	char	   *sep;
+	const char *sep;
 	char	   *endp;
 	long		result;
 

src/interfaces/ecpg/pgtypeslib/datetime.c

@@ -335,8 +335,8 @@ PGTYPESdate_defmt_asc(date * d, const char *fmt, const char *str)
 	 */
 	int			token[3][2];
 	int			token_values[3] = {-1, -1, -1};
-	char	   *fmt_token_order;
-	char	   *fmt_ystart,
+	const char *fmt_token_order;
+	const char *fmt_ystart,
 			   *fmt_mstart,
 			   *fmt_dstart;
 	unsigned int i;

src/interfaces/ecpg/preproc/ecpg.trailer

@@ -1975,12 +1975,14 @@ civarind: cvariable indicator
 
 char_civar: char_variable
 	{
-		char	   *ptr = strstr(@1, ".arr");
+		char	   *var = loc_strdup(@1);
+		char	   *ptr = strstr(var, ".arr");
 
 		if (ptr)				/* varchar, we need the struct name here, not
 								 * the struct element */
 			*ptr = '\0';
-		add_variable_to_head(&argsinsert, find_variable(@1), &no_indicator);
+		add_variable_to_head(&argsinsert, find_variable(var), &no_indicator);
+		@$ = var;
 	}
 	;
 

src/port/chklocale.c

@@ -202,7 +202,7 @@ static char *
 win32_get_codeset(const char *ctype)
 {
 	char	   *r = NULL;
-	char	   *codepage;
+	const char *codepage;
 	uint32		cp;
 	WCHAR		wctype[LOCALE_NAME_MAX_LENGTH];
 

src/port/getopt_long.c

@@ -62,7 +62,7 @@ getopt_long(int argc, char *const argv[],
 			const struct option *longopts, int *longindex)
 {
 	static char *place = EMSG;	/* option letter processing */
-	char	   *oli;			/* option letter list index */
+	const char *oli;			/* option letter list index */
 	static int	nonopt_start = -1;
 	static bool force_nonopt = false;
 

src/port/win32setlocale.c

@@ -119,9 +119,9 @@ map_locale(const struct locale_map *map, const char *locale)
 		const char *needle_start = map[i].locale_name_start;
 		const char *needle_end = map[i].locale_name_end;
 		const char *replacement = map[i].replacement;
-		char	   *match;
-		char	   *match_start = NULL;
-		char	   *match_end = NULL;
+		const char *match;
+		const char *match_start = NULL;
+		const char *match_end = NULL;
 
 		match = strstr(locale, needle_start);
 		if (match)
@@ -148,7 +148,7 @@ map_locale(const struct locale_map *map, const char *locale)
 			/* Found a match. Replace the matched string. */
 			int			matchpos = match_start - locale;
 			int			replacementlen = strlen(replacement);
-			char	   *rest = match_end;
+			const char *rest = match_end;
 			int			restlen = strlen(rest);
 
 			/* check that the result fits in the static buffer */

src/test/regress/pg_regress.c

@@ -693,7 +693,7 @@ static
 const char *
 get_expectfile(const char *testname, const char *file)
 {
-	char	   *file_type;
+	const char *file_type;
 	_resultmap *rm;
 
 	/*

src/timezone/zic.c

@@ -2620,7 +2620,7 @@ doabbr(char *abbr, struct zone const *zp, char const *letters,
 	   bool isdst, zic_t save, bool doquotes)
 {
 	char	   *cp;
-	char	   *slashp;
+	char const *slashp;
 	size_t		len;
 	char const *format = zp->z_format;