In ALTER COLUMN TYPE, strip any implicit coercion operations appearing

at the top level of the column's old default expression before adding
an implicit coercion to the new column type.  This seems to satisfy the
principle of least surprise, as per discussion of bug #1290.

1 files changed, 36 insertions, 1 deletions

diff --git a/src/backend/optimizer/util/clauses.c b/src/backend/optimizer/util/clauses.c
index b6ac7786aa7..0f7d8dc31fc 100644
--- a/src/backend/optimizer/util/clauses.c
+++ b/src/backend/optimizer/util/clauses.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/util/clauses.c,v 1.182 2004/10/07 18:38:49 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/util/clauses.c,v 1.183 2004/10/22 17:20:05 tgl Exp $
  *
  * HISTORY
  *	  AUTHOR			DATE			MAJOR EVENT
@@ -1022,6 +1022,41 @@ CommuteClause(OpExpr *clause)
 }
 
 /*
+ * strip_implicit_coercions: remove implicit coercions at top level of tree
+ *
+ * Note: there isn't any useful thing we can do with a RowExpr here, so
+ * just return it unchanged, even if it's marked as an implicit coercion.
+ */
+Node *
+strip_implicit_coercions(Node *node)
+{
+	if (node == NULL)
+		return NULL;
+	if (IsA(node, FuncExpr))
+	{
+		FuncExpr   *f = (FuncExpr *) node;
+
+		if (f->funcformat == COERCE_IMPLICIT_CAST)
+			return strip_implicit_coercions(linitial(f->args));
+	}
+	else if (IsA(node, RelabelType))
+	{
+		RelabelType *r = (RelabelType *) node;
+
+		if (r->relabelformat == COERCE_IMPLICIT_CAST)
+			return strip_implicit_coercions((Node *) r->arg);
+	}
+	else if (IsA(node, CoerceToDomain))
+	{
+		CoerceToDomain *c = (CoerceToDomain *) node;
+
+		if (c->coercionformat == COERCE_IMPLICIT_CAST)
+			return strip_implicit_coercions((Node *) c->arg);
+	}
+	return node;
+}
+
+/*
  * set_coercionform_dontcare: set all CoercionForm fields to COERCE_DONTCARE
  *
  * This is used to make index expressions and index predicates more easily