Throw an appropriate error if ALTER COLUMN TYPE finds a dependent trigger.

Actually making this case work, if the column is used in the trigger's
WHEN condition, will take some new code that probably isn't appropriate
to back-patch.  For now, just throw a FEATURE_NOT_SUPPORTED error rather
than allowing control to reach the "unexpected object" case.  Per bug #5688
from Daniel Grace.  Back-patch to 9.0 where the possibility of such a
dependency was introduced.

diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index c4d81bb4fecb6c1edb58ca8eebaaa5478028e22d..ab9c6a5191dfb37ba438cc5d894899fb508088ae 100644 (file)
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -6148,6 +6148,24 @@ ATExecAlterColumnType(AlteredTableInfo *tab, Relation rel,
                                   colName)));
                break;
 
+           case OCLASS_TRIGGER:
+               /*
+                * A trigger can depend on a column because the column is
+                * specified as an update target, or because the column is
+                * used in the trigger's WHEN condition.  The first case would
+                * not require any extra work, but the second case would
+                * require updating the WHEN expression, which will take a
+                * significant amount of new code.  Since we can't easily tell
+                * which case applies, we punt for both.  FIXME someday.
+                */
+               ereport(ERROR,
+                       (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+                        errmsg("cannot alter type of a column used in a trigger definition"),
+                        errdetail("%s depends on column \"%s\"",
+                                  getObjectDescription(&foundObject),
+                                  colName)));
+               break;
+
            case OCLASS_DEFAULT:
 
                /*
@@ -6168,7 +6186,6 @@ ATExecAlterColumnType(AlteredTableInfo *tab, Relation rel,
            case OCLASS_OPFAMILY:
            case OCLASS_AMOP:
            case OCLASS_AMPROC:
-           case OCLASS_TRIGGER:
            case OCLASS_SCHEMA:
            case OCLASS_TSPARSER:
            case OCLASS_TSDICT: