Improve reporting of run-time-detected indeterminate-collation errors.

pg_newlocale_from_collation does not have enough context to give an error
message that's even a little bit useful, so move the responsibility for
complaining up to its callers.  Also, reword ERRCODE_INDETERMINATE_COLLATION
error messages in a less jargony, more message-style-guide-compliant
fashion.

src/backend/commands/collationcmds.c

@@ -141,7 +141,7 @@ DefineCollation(List *names, List *parameters)
 
 	/* check that the locales can be loaded */
 	CommandCounterIncrement();
-	pg_newlocale_from_collation(newoid);
+	(void) pg_newlocale_from_collation(newoid);
 }
 
 /*

src/backend/commands/indexcmds.c

@@ -899,7 +899,7 @@ ComputeIndexAttrs(IndexInfo *indexInfo,
 			if (!OidIsValid(attcollation))
 				ereport(ERROR,
 						(errcode(ERRCODE_INDETERMINATE_COLLATION),
-						 errmsg("no collation was derived for the index expression"),
+						 errmsg("could not determine which collation to use for index expression"),
 						 errhint("Use the COLLATE clause to set the collation explicitly.")));
 		}
 		else

src/backend/commands/view.c

@@ -139,7 +139,7 @@ DefineVirtualRelation(const RangeVar *relation, List *tlist, bool replace)
 				if (!OidIsValid(def->collOid))
 					ereport(ERROR,
 							(errcode(ERRCODE_INDETERMINATE_COLLATION),
-							 errmsg("no collation was derived for view column \"%s\"",
+							 errmsg("could not determine which collation to use for view column \"%s\"",
 									def->colname),
 							 errhint("Use the COLLATE clause to set the collation explicitly.")));
 			}

src/backend/utils/adt/formatting.c

@@ -1503,7 +1503,20 @@ str_tolower(const char *buff, size_t nbytes, Oid collid)
 		size_t		result_size;
 
 		if (collid != DEFAULT_COLLATION_OID)
+		{
+			if (!OidIsValid(collid))
+			{
+				/*
+				 * This typically means that the parser could not resolve a
+				 * conflict of implicit collations, so report it that way.
+				 */
+				ereport(ERROR,
+						(errcode(ERRCODE_INDETERMINATE_COLLATION),
+						 errmsg("could not determine which collation to use for lower() function"),
+						 errhint("Use the COLLATE clause to set the collation explicitly.")));
+			}
 			mylocale = pg_newlocale_from_collation(collid);
+		}
 
 		/* Overflow paranoia */
 		if ((nbytes + 1) > (INT_MAX / sizeof(wchar_t)))
@@ -1540,7 +1553,20 @@ str_tolower(const char *buff, size_t nbytes, Oid collid)
 		char	   *p;
 
 		if (collid != DEFAULT_COLLATION_OID)
+		{
+			if (!OidIsValid(collid))
+			{
+				/*
+				 * This typically means that the parser could not resolve a
+				 * conflict of implicit collations, so report it that way.
+				 */
+				ereport(ERROR,
+						(errcode(ERRCODE_INDETERMINATE_COLLATION),
+						 errmsg("could not determine which collation to use for lower() function"),
+						 errhint("Use the COLLATE clause to set the collation explicitly.")));
+			}
 			mylocale = pg_newlocale_from_collation(collid);
+		}
 
 		result = pnstrdup(buff, nbytes);
 
@@ -1598,7 +1624,20 @@ str_toupper(const char *buff, size_t nbytes, Oid collid)
 		size_t		result_size;
 
 		if (collid != DEFAULT_COLLATION_OID)
+		{
+			if (!OidIsValid(collid))
+			{
+				/*
+				 * This typically means that the parser could not resolve a
+				 * conflict of implicit collations, so report it that way.
+				 */
+				ereport(ERROR,
+						(errcode(ERRCODE_INDETERMINATE_COLLATION),
+						 errmsg("could not determine which collation to use for upper() function"),
+						 errhint("Use the COLLATE clause to set the collation explicitly.")));
+			}
 			mylocale = pg_newlocale_from_collation(collid);
+		}
 
 		/* Overflow paranoia */
 		if ((nbytes + 1) > (INT_MAX / sizeof(wchar_t)))
@@ -1635,7 +1674,20 @@ str_toupper(const char *buff, size_t nbytes, Oid collid)
 		char	   *p;
 
 		if (collid != DEFAULT_COLLATION_OID)
+		{
+			if (!OidIsValid(collid))
+			{
+				/*
+				 * This typically means that the parser could not resolve a
+				 * conflict of implicit collations, so report it that way.
+				 */
+				ereport(ERROR,
+						(errcode(ERRCODE_INDETERMINATE_COLLATION),
+						 errmsg("could not determine which collation to use for upper() function"),
+						 errhint("Use the COLLATE clause to set the collation explicitly.")));
+			}
 			mylocale = pg_newlocale_from_collation(collid);
+		}
 
 		result = pnstrdup(buff, nbytes);
 
@@ -1705,7 +1757,20 @@ str_initcap(const char *buff, size_t nbytes, Oid collid)
 		size_t		result_size;
 
 		if (collid != DEFAULT_COLLATION_OID)
+		{
+			if (!OidIsValid(collid))
+			{
+				/*
+				 * This typically means that the parser could not resolve a
+				 * conflict of implicit collations, so report it that way.
+				 */
+				ereport(ERROR,
+						(errcode(ERRCODE_INDETERMINATE_COLLATION),
+						 errmsg("could not determine which collation to use for initcap() function"),
+						 errhint("Use the COLLATE clause to set the collation explicitly.")));
+			}
 			mylocale = pg_newlocale_from_collation(collid);
+		}
 
 		/* Overflow paranoia */
 		if ((nbytes + 1) > (INT_MAX / sizeof(wchar_t)))
@@ -1754,7 +1819,20 @@ str_initcap(const char *buff, size_t nbytes, Oid collid)
 		char	   *p;
 
 		if (collid != DEFAULT_COLLATION_OID)
+		{
+			if (!OidIsValid(collid))
+			{
+				/*
+				 * This typically means that the parser could not resolve a
+				 * conflict of implicit collations, so report it that way.
+				 */
+				ereport(ERROR,
+						(errcode(ERRCODE_INDETERMINATE_COLLATION),
+						 errmsg("could not determine which collation to use for initcap() function"),
+						 errhint("Use the COLLATE clause to set the collation explicitly.")));
+			}
 			mylocale = pg_newlocale_from_collation(collid);
+		}
 
 		result = pnstrdup(buff, nbytes);
 

src/backend/utils/adt/pg_locale.c

@@ -932,21 +932,13 @@ pg_newlocale_from_collation(Oid collid)
 {
 	collation_cache_entry *cache_entry;
 
+	/* Callers must pass a valid OID */
+	Assert(OidIsValid(collid));
+
 	/* Return 0 for "default" collation, just in case caller forgets */
 	if (collid == DEFAULT_COLLATION_OID)
 		return (pg_locale_t) 0;
 
-	/*
-	 * This is where we'll fail if a collation-aware function is invoked
-	 * and no collation OID is passed.  This typically means that the
-	 * parser could not resolve a conflict of implicit collations, so
-	 * report it that way.
-	 */
-	if (!OidIsValid(collid))
-		ereport(ERROR,
-				(errcode(ERRCODE_INDETERMINATE_COLLATION),
-				 errmsg("locale operation to be invoked, but no collation was derived")));
-
 	cache_entry = lookup_collation_cache(collid, false);
 
 	if (cache_entry->locale == 0)

src/backend/utils/adt/varlena.c

@@ -1302,7 +1302,20 @@ varstr_cmp(char *arg1, int len1, char *arg2, int len2, Oid collid)
 		pg_locale_t	mylocale = 0;
 
 		if (collid != DEFAULT_COLLATION_OID)
+		{
+			if (!OidIsValid(collid))
+			{
+				/*
+				 * This typically means that the parser could not resolve a
+				 * conflict of implicit collations, so report it that way.
+				 */
+				ereport(ERROR,
+						(errcode(ERRCODE_INDETERMINATE_COLLATION),
+						 errmsg("could not determine which collation to use for string comparison"),
+						 errhint("Use the COLLATE clause to set the collation explicitly.")));
+			}
 			mylocale = pg_newlocale_from_collation(collid);
+		}
 
 #ifdef WIN32
 		/* Win32 does not have UTF-8, so we need to map to UTF-16 */

src/test/regress/expected/collate.linux.utf8.out

@@ -586,7 +586,8 @@ SELECT a, b FROM collate_test3 EXCEPT SELECT a, b FROM collate_test3 WHERE a < 2
 (3 rows)
 
 SELECT a, b FROM collate_test1 UNION ALL SELECT a, b FROM collate_test3 ORDER BY 2; -- fail
-ERROR:  locale operation to be invoked, but no collation was derived
+ERROR:  could not determine which collation to use for string comparison
+HINT:  Use the COLLATE clause to set the collation explicitly.
 SELECT a, b FROM collate_test1 UNION ALL SELECT a, b FROM collate_test3; -- ok
  a |  b  
 ---+-----
@@ -629,7 +630,8 @@ ERROR:  no collation was derived for column "b" with collatable type text
 HINT:  Use the COLLATE clause to set the collation explicitly.
 -- ideally this would be a parse-time error, but for now it must be run-time:
 select x < y from collate_test10; -- fail
-ERROR:  locale operation to be invoked, but no collation was derived
+ERROR:  could not determine which collation to use for string comparison
+HINT:  Use the COLLATE clause to set the collation explicitly.
 select x || y from collate_test10; -- ok, because || is not collation aware
  ?column? 
 ----------

src/test/regress/expected/collate.out

@@ -392,7 +392,8 @@ SELECT a, b FROM collate_test2 EXCEPT SELECT a, b FROM collate_test2 WHERE a < 2
 (3 rows)
 
 SELECT a, b FROM collate_test1 UNION ALL SELECT a, b FROM collate_test2 ORDER BY 2; -- fail
-ERROR:  locale operation to be invoked, but no collation was derived
+ERROR:  could not determine which collation to use for string comparison
+HINT:  Use the COLLATE clause to set the collation explicitly.
 SELECT a, b FROM collate_test1 UNION ALL SELECT a, b FROM collate_test2; -- ok
  a |  b  
 ---+-----
@@ -435,7 +436,8 @@ ERROR:  no collation was derived for column "b" with collatable type text
 HINT:  Use the COLLATE clause to set the collation explicitly.
 -- ideally this would be a parse-time error, but for now it must be run-time:
 select x < y from collate_test10; -- fail
-ERROR:  locale operation to be invoked, but no collation was derived
+ERROR:  could not determine which collation to use for string comparison
+HINT:  Use the COLLATE clause to set the collation explicitly.
 select x || y from collate_test10; -- ok, because || is not collation aware
  ?column? 
 ----------