[m-rev.] diff: fix unbound variable bug in erlang backend

[Peter Wang]

Estimated hours taken: 0.5
Branches: main

compiler/erl_code_gen.m:
	Fix a bug in the Erlang code generator where a call to a predicate
	with determinism `failure' can be followed by references to unbound
	variables.

tests/valid/Mmakefile:
tests/valid/call_failure.m:
	Add test case.

Index: compiler/erl_code_gen.m
===================================================================
RCS file: /home/mercury/mercury1/repository/mercury/compiler/erl_code_gen.m,v
retrieving revision 1.27
diff -u -r1.27 erl_code_gen.m
--- compiler/erl_code_gen.m	3 Oct 2007 03:33:24 -0000	1.27
+++ compiler/erl_code_gen.m	4 Oct 2007 05:20:05 -0000
@@ -473,6 +473,13 @@
             % aborted before binding them).
             MaybeSuccessExpr = no
         ;
+            Determinism = detism_failure
+        ->
+            % This goal can't succeed.  As above we don't want to pass a
+            % success expression, but we must pass something to maintain the
+            % invariant that a model_semi goal has a success expression.
+            MaybeSuccessExpr = yes(elds_term(elds_fail))
+        ;
             MaybeSuccessExpr = MaybeSuccessExpr0
         ),
         erl_gen_goal_expr(GoalExpr, GoalCodeModel, Determinism, InstMap,
Index: tests/valid/Mmakefile
===================================================================
RCS file: /home/mercury/mercury1/repository/tests/valid/Mmakefile,v
retrieving revision 1.197
diff -u -r1.197 Mmakefile
--- tests/valid/Mmakefile	4 Oct 2007 00:36:52 -0000	1.197
+++ tests/valid/Mmakefile	4 Oct 2007 05:20:05 -0000
@@ -61,6 +61,7 @@
 	any_matches_bound \
 	big_foreign_type \
 	builtin_false \
+	call_failure \
 	common_struct_bug \
 	compl_unify_bug \
 	complicated_unify \
Index: tests/valid/call_failure.m
===================================================================
RCS file: tests/valid/call_failure.m
diff -N tests/valid/call_failure.m
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ tests/valid/call_failure.m	4 Oct 2007 05:20:05 -0000
@@ -0,0 +1,24 @@
+:- module call_failure.
+:- interface.
+
+:- pred foo(int::in, int::out) is failure.
+
+:- implementation.
+
+:- import_module int.
+:- import_module require.
+
+foo(X, Y) :-
+    ( X = 42 ->
+        bar(X, Y0),
+        Y = Y0 + 1
+    ;
+        error("foo")
+    ).
+
+:- pred bar(int, int).
+:- mode bar(in(bound(42)), out) is failure.
+:- pragma no_inline(bar/2).
+
+bar(42, _) :-
+    fail.

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