Provide more-specific error details/hints for function lookup failures.

Up to now we've contented ourselves with a one-size-fits-all error
hint when we fail to find any match to a function or procedure call.
That was mostly okay in the beginning, but it was never great, and
since the introduction of named arguments it's really not adequate.
We at least ought to distinguish "function name doesn't exist" from
"function name exists, but not with those argument names".  And the
rules for named-argument matching are arcane enough that some more
detail seems warranted if we match the argument names but the call
still doesn't work.

This patch creates a framework for dealing with these problems:
FuncnameGetCandidates and related code will now pass back a bitmask of
flags showing how far the match succeeded.  This allows a considerable
amount of granularity in the reports.  The set-bits-in-a-bitmask
approach means that when there are multiple candidate functions, the
report will reflect the match(es) that got the furthest, which seems
correct.  Also, we can avoid mentioning "maybe add casts" unless
failure to match argument types is actually the issue.

Extend the same return-a-bitmask approach to OpernameGetCandidates.
The issues around argument names don't apply to operator syntax,
but it still seems worth distinguishing between "there is no
operator of that name" and "we couldn't match the argument types".

While at it, adjust these messages and related ones to more strictly
separate "detail" from "hint", following our message style guidelines'
distinction between those.

Reported-by: Dominique Devienne <ddevienne@gmail.com>
Author: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: Robert Haas <robertmhaas@gmail.com>
Discussion: https://postgr.es/m/1756041.1754616558@sss.pgh.pa.us

2 files changed, 15 insertions, 6 deletions

diff --git a/src/backend/utils/adt/regproc.c b/src/backend/utils/adt/regproc.c
index af17a3421a0..e5c2246f2c9 100644
--- a/src/backend/utils/adt/regproc.c
+++ b/src/backend/utils/adt/regproc.c
@@ -71,6 +71,7 @@ regprocin(PG_FUNCTION_ARGS)
 	RegProcedure result;
 	List	   *names;
 	FuncCandidateList clist;
+	int			fgc_flags;
 
 	/* Handle "-" or numeric OID */
 	if (parseDashOrOid(pro_name_or_oid, &result, escontext))
@@ -93,7 +94,8 @@ regprocin(PG_FUNCTION_ARGS)
 	if (names == NIL)
 		PG_RETURN_NULL();
 
-	clist = FuncnameGetCandidates(names, -1, NIL, false, false, false, true);
+	clist = FuncnameGetCandidates(names, -1, NIL, false, false, false, true,
+								  &fgc_flags);
 
 	if (clist == NULL)
 		ereturn(escontext, (Datum) 0,
@@ -164,13 +166,15 @@ regprocout(PG_FUNCTION_ARGS)
 		{
 			char	   *nspname;
 			FuncCandidateList clist;
+			int			fgc_flags;
 
 			/*
 			 * Would this proc be found (uniquely!) by regprocin? If not,
 			 * qualify it.
 			 */
 			clist = FuncnameGetCandidates(list_make1(makeString(proname)),
-										  -1, NIL, false, false, false, false);
+										  -1, NIL, false, false, false, false,
+										  &fgc_flags);
 			if (clist != NULL && clist->next == NULL &&
 				clist->oid == proid)
 				nspname = NULL;
@@ -231,6 +235,7 @@ regprocedurein(PG_FUNCTION_ARGS)
 	int			nargs;
 	Oid			argtypes[FUNC_MAX_ARGS];
 	FuncCandidateList clist;
+	int			fgc_flags;
 
 	/* Handle "-" or numeric OID */
 	if (parseDashOrOid(pro_name_or_oid, &result, escontext))
@@ -251,8 +256,8 @@ regprocedurein(PG_FUNCTION_ARGS)
 							  escontext))
 		PG_RETURN_NULL();
 
-	clist = FuncnameGetCandidates(names, nargs, NIL, false, false,
-								  false, true);
+	clist = FuncnameGetCandidates(names, nargs, NIL, false, false, false, true,
+								  &fgc_flags);
 
 	for (; clist; clist = clist->next)
 	{
@@ -483,6 +488,7 @@ regoperin(PG_FUNCTION_ARGS)
 	Oid			result;
 	List	   *names;
 	FuncCandidateList clist;
+	int			fgc_flags;
 
 	/* Handle "0" or numeric OID */
 	if (parseNumericOid(opr_name_or_oid, &result, escontext))
@@ -502,7 +508,7 @@ regoperin(PG_FUNCTION_ARGS)
 	if (names == NIL)
 		PG_RETURN_NULL();
 
-	clist = OpernameGetCandidates(names, '\0', true);
+	clist = OpernameGetCandidates(names, '\0', true, &fgc_flags);
 
 	if (clist == NULL)
 		ereturn(escontext, (Datum) 0,
@@ -572,13 +578,14 @@ regoperout(PG_FUNCTION_ARGS)
 		else
 		{
 			FuncCandidateList clist;
+			int			fgc_flags;
 
 			/*
 			 * Would this oper be found (uniquely!) by regoperin? If not,
 			 * qualify it.
 			 */
 			clist = OpernameGetCandidates(list_make1(makeString(oprname)),
-										  '\0', false);
+										  '\0', false, &fgc_flags);
 			if (clist != NULL && clist->next == NULL &&
 				clist->oid == oprid)
 				result = pstrdup(oprname);
diff --git a/src/backend/utils/adt/ruleutils.c b/src/backend/utils/adt/ruleutils.c
index 3d6e6bdbfd2..0408a95941d 100644
--- a/src/backend/utils/adt/ruleutils.c
+++ b/src/backend/utils/adt/ruleutils.c
@@ -13265,6 +13265,7 @@ generate_function_name(Oid funcid, int nargs, List *argnames, Oid *argtypes,
 	bool		use_variadic;
 	char	   *nspname;
 	FuncDetailCode p_result;
+	int			fgc_flags;
 	Oid			p_funcid;
 	Oid			p_rettype;
 	bool		p_retset;
@@ -13323,6 +13324,7 @@ generate_function_name(Oid funcid, int nargs, List *argnames, Oid *argtypes,
 		p_result = func_get_detail(list_make1(makeString(proname)),
 								   NIL, argnames, nargs, argtypes,
 								   !use_variadic, true, false,
+								   &fgc_flags,
 								   &p_funcid, &p_rettype,
 								   &p_retset, &p_nvargs, &p_vatype,
 								   &p_true_typeids, NULL);