Fix get_expr_result_type() to find field names for RECORD Consts.

tglsfdc · tglsfdc · commit 8a15b4178c40 · 2023-09-15T16:39:27.000-04:00
This is a back-patch of commit d575347 ("Fix EXPLAIN of SEARCH BREADTH FIRST with a constant initial value") into pre-v14 branches. At the time I'd thought it was not needed in branches that lack the SEARCH/CYCLE feature, but that was just a failure of imagination. It's possible to demonstrate "record type has not been registered" failures in older branches too, during deparsing of views that contain references to fields of composite constants. Back-patch only the code changes, as the test cases added by d575347 all require SEARCH/CYCLE syntax. A suitable test case will be added in the upcoming fix for bug #18077. Discussion: https://postgr.es/m/17644-3bd1f3036d6d7a16@postgresql.org Discussion: https://postgr.es/m/3607145.1694803130@sss.pgh.pa.us
diff --git a/src/backend/utils/adt/ruleutils.c b/src/backend/utils/adt/ruleutils.c
@@ -7018,7 +7018,8 @@ get_name_for_var_field(Var *var, int fieldno,
 
 	/*
 	 * If it's a RowExpr that was expanded from a whole-row Var, use the
-	 * column names attached to it.
+	 * column names attached to it.  (We could let get_expr_result_tupdesc()
+	 * handle this, but it's much cheaper to just pull out the name we need.)
 	 */
 	if (IsA(var, RowExpr))
 	{
diff --git a/src/backend/utils/fmgr/funcapi.c b/src/backend/utils/fmgr/funcapi.c
@@ -268,6 +268,40 @@ get_expr_result_type(Node *expr,
 			*resultTupleDesc = BlessTupleDesc(tupdesc);
 		return TYPEFUNC_COMPOSITE;
 	}
+	else if (expr && IsA(expr, Const) &&
+			 ((Const *) expr)->consttype == RECORDOID &&
+			 !((Const *) expr)->constisnull)
+	{
+		/*
+		 * When EXPLAIN'ing some queries with SEARCH/CYCLE clauses, we may
+		 * need to resolve field names of a RECORD-type Const.  The datum
+		 * should contain a typmod that will tell us that.
+		 */
+		HeapTupleHeader rec;
+		Oid			tupType;
+		int32		tupTypmod;
+
+		rec = DatumGetHeapTupleHeader(((Const *) expr)->constvalue);
+		tupType = HeapTupleHeaderGetTypeId(rec);
+		tupTypmod = HeapTupleHeaderGetTypMod(rec);
+		if (resultTypeId)
+			*resultTypeId = tupType;
+		if (tupType != RECORDOID || tupTypmod >= 0)
+		{
+			/* Should be able to look it up */
+			if (resultTupleDesc)
+				*resultTupleDesc = lookup_rowtype_tupdesc_copy(tupType,
+															   tupTypmod);
+			return TYPEFUNC_COMPOSITE;
+		}
+		else
+		{
+			/* This shouldn't really happen ... */
+			if (resultTupleDesc)
+				*resultTupleDesc = NULL;
+			return TYPEFUNC_RECORD;
+		}
+	}
 	else
 	{
 		/* handle as a generic expression; no chance to resolve RECORD */

Original file line number	Diff line number	Diff line change
`@@ -7018,7 +7018,8 @@ get_name_for_var_field(Var *var, int fieldno,`
`7018`	`7018`
`7019`	`7019`	`/*`
`7020`	`7020`	`* If it's a RowExpr that was expanded from a whole-row Var, use the`
`7021`		`- * column names attached to it.`
	`7021`	`+ * column names attached to it. (We could let get_expr_result_tupdesc()`
	`7022`	`+ * handle this, but it's much cheaper to just pull out the name we need.)`
`7022`	`7023`	`*/`
`7023`	`7024`	`if (IsA(var, RowExpr))`
`7024`	`7025`	`{`