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

This is a back-patch of commit d57534740 ("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 d57534740
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
index 6d33b482a754098f78e403e7cb8089d1709492cf..90dd6ef25c672225b6da4acfa56380e767aa7a6d 100644 (file)
--- a/src/backend/utils/adt/ruleutils.c
+++ b/src/backend/utils/adt/ruleutils.c
@@ -6944,7 +6944,8 @@ 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
index cab34c323b03d821ad5f85b9e7d022b05e38b992..a9eb5b0029f739aa0c45af56c268c318c048d586 100644 (file)
--- a/src/backend/utils/fmgr/funcapi.c
+++ b/src/backend/utils/fmgr/funcapi.c
@@ -283,6 +283,40 @@ 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 */