Change post-rewriter representation of dropped columns in joinaliasvars.

It's possible to drop a column from an input table of a JOIN clause in a
view, if that column is nowhere actually referenced in the view.  But it
will still be there in the JOIN clause's joinaliasvars list.  We used to
replace such entries with NULL Const nodes, which is handy for generation
of RowExpr expansion of a whole-row reference to the view.  The trouble
with that is that it can't be distinguished from the situation after
subquery pull-up of a constant subquery output expression below the JOIN.
Instead, replace such joinaliasvars with null pointers (empty expression
trees), which can't be confused with pulled-up expressions.  expandRTE()
still emits the old convention, though, for convenience of RowExpr
generation and to reduce the risk of breaking extension code.

In HEAD and 9.3, this patch also fixes a problem with some new code in
ruleutils.c that was failing to cope with implicitly-casted joinaliasvars
entries, as per recent report from Feike Steenbergen.  That oversight was
because of an inadequate description of the data structure in parsenodes.h,
which I've now corrected.  There were some pre-existing oversights of the
same ilk elsewhere, which I believe are now all fixed.

1 files changed, 22 insertions, 17 deletions

diff --git a/src/backend/utils/adt/ruleutils.c b/src/backend/utils/adt/ruleutils.c
index 40b565a11d6..cecb5427271 100644
--- a/src/backend/utils/adt/ruleutils.c
+++ b/src/backend/utils/adt/ruleutils.c
@@ -235,6 +235,7 @@ typedef struct
 	 * child RTE's attno and rightattnos[i] is zero; and conversely for a
 	 * column of the right child.  But for merged columns produced by JOIN
 	 * USING/NATURAL JOIN, both leftattnos[i] and rightattnos[i] are nonzero.
+	 * Also, if the column has been dropped, both are zero.
 	 *
 	 * If it's a JOIN USING, usingNames holds the alias names selected for the
 	 * merged columns (these might be different from the original USING list,
@@ -3053,6 +3054,13 @@ set_join_column_names(deparse_namespace *dpns, RangeTblEntry *rte,
 		char	   *colname = colinfo->colnames[i];
 		char	   *real_colname;
 
+		/* Ignore dropped column (only possible for non-merged column) */
+		if (colinfo->leftattnos[i] == 0 && colinfo->rightattnos[i] == 0)
+		{
+			Assert(colname == NULL);
+			continue;
+		}
+
 		/* Get the child column name */
 		if (colinfo->leftattnos[i] > 0)
 			real_colname = leftcolinfo->colnames[colinfo->leftattnos[i] - 1];
@@ -3061,15 +3069,9 @@ set_join_column_names(deparse_namespace *dpns, RangeTblEntry *rte,
 		else
 		{
 			/* We're joining system columns --- use eref name */
-			real_colname = (char *) list_nth(rte->eref->colnames, i);
-		}
-
-		/* Ignore dropped columns (only possible for non-merged column) */
-		if (real_colname == NULL)
-		{
-			Assert(colname == NULL);
-			continue;
+			real_colname = strVal(list_nth(rte->eref->colnames, i));
 		}
+		Assert(real_colname != NULL);
 
 		/* In an unnamed join, just report child column names as-is */
 		if (rte->alias == NULL)
@@ -3402,7 +3404,14 @@ identify_join_columns(JoinExpr *j, RangeTblEntry *jrte,
 	{
 		Var		   *aliasvar = (Var *) lfirst(lc);
 
-		if (IsA(aliasvar, Var))
+		/* get rid of any implicit coercion above the Var */
+		aliasvar = (Var *) strip_implicit_coercions((Node *) aliasvar);
+
+		if (aliasvar == NULL)
+		{
+			/* It's a dropped column; nothing to do here */
+		}
+		else if (IsA(aliasvar, Var))
 		{
 			Assert(aliasvar->varlevelsup == 0);
 			Assert(aliasvar->varattno != 0);
@@ -3422,15 +3431,8 @@ identify_join_columns(JoinExpr *j, RangeTblEntry *jrte,
 			 */
 		}
 		else
-		{
-			/*
-			 * Although NULL constants can appear in joinaliasvars lists
-			 * during planning, we shouldn't see any here, since the Query
-			 * tree hasn't been through AcquireRewriteLocks().
-			 */
 			elog(ERROR, "unrecognized node type in join alias vars: %d",
 				 (int) nodeTag(aliasvar));
-		}
 
 		i++;
 	}
@@ -5359,7 +5361,8 @@ get_variable(Var *var, int levelsup, bool istoplevel, deparse_context *context)
 			Var		   *aliasvar;
 
 			aliasvar = (Var *) list_nth(rte->joinaliasvars, attnum - 1);
-			if (IsA(aliasvar, Var))
+			/* we intentionally don't strip implicit coercions here */
+			if (aliasvar && IsA(aliasvar, Var))
 			{
 				return get_variable(aliasvar, var->varlevelsup + levelsup,
 									istoplevel, context);
@@ -5670,6 +5673,8 @@ get_name_for_var_field(Var *var, int fieldno,
 				elog(ERROR, "cannot decompile join alias var in plan tree");
 			Assert(attnum > 0 && attnum <= list_length(rte->joinaliasvars));
 			expr = (Node *) list_nth(rte->joinaliasvars, attnum - 1);
+			Assert(expr != NULL);
+			/* we intentionally don't strip implicit coercions here */
 			if (IsA(expr, Var))
 				return get_name_for_var_field((Var *) expr, fieldno,
 											  var->varlevelsup + levelsup,