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

5 files changed, 10 insertions, 9 deletions

diff --git a/src/backend/catalog/pg_type.c b/src/backend/catalog/pg_type.c
index 257c7da8568..4a69a81b9fb 100644
--- a/src/backend/catalog/pg_type.c
+++ b/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
diff --git a/src/backend/tsearch/spell.c b/src/backend/tsearch/spell.c
index 146801885d7..0dab31f0ddb 100644
--- a/src/backend/tsearch/spell.c
+++ b/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)
 		{
diff --git a/src/backend/utils/adt/formatting.c b/src/backend/utils/adt/formatting.c
index 5bfeda2ffde..c3cb022a400 100644
--- a/src/backend/utils/adt/formatting.c
+++ b/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
diff --git a/src/backend/utils/adt/pg_locale.c b/src/backend/utils/adt/pg_locale.c
index b26257c0a8d..d73bab97c15 100644
--- a/src/backend/utils/adt/pg_locale.c
+++ b/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;
 
diff --git a/src/backend/utils/adt/xid8funcs.c b/src/backend/utils/adt/xid8funcs.c
index a211a107767..4b3f7a69b3b 100644
--- a/src/backend/utils/adt/xid8funcs.c
+++ b/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);