[m-rev.] for review: fix state var compiler abort

[Zoltan Somogyi]

For post-commit review by Ralph. The diff changes behavior only in cases where
the compiler used to abort.

Ralph, if you could document the intended semantics of the fields of the
svar_info type, including the invariants that they are supposed to obey,
I would be grateful.

Zoltan.

Fix a compiler abort reported by obo at ruk.cuni.cz.

compiler/make_hlds.m:
	Avoid a compiler abort for clauses of the form p(!:X).

tests/invalid/state_vars_test5.{m,err_exp}:
	New test case to check for a meaningful error message for such code.

tests/invalid/Mmakefile:
	Enable the new test case.

cvs diff: Diffing .
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cvs diff: Diffing bindist
cvs diff: Diffing boehm_gc
cvs diff: Diffing boehm_gc/Mac_files
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Index: compiler/make_hlds.m
===================================================================
RCS file: /home/mercury/mercury1/repository/mercury/compiler/make_hlds.m,v
retrieving revision 1.459
diff -u -b -r1.459 make_hlds.m
--- compiler/make_hlds.m	21 Dec 2003 05:04:35 -0000	1.459
+++ compiler/make_hlds.m	6 Mar 2004 06:39:55 -0000
@@ -9160,13 +9160,17 @@
 :- func svar_unifiers(prog_context, svar_map, svar_map) = hlds_goals.
 
 svar_unifiers(Context, LHSMap, RHSMap) =
-	map__foldl(
-		func(StateVar, Var, Unifiers) =
-			  [ svar_unification(Context,
-			  	Var, RHSMap ^ det_elem(StateVar))
-			  | Unifiers ],
-		LHSMap,
-		[]
+	map__foldl(add_svar_unifier(RHSMap, Context), LHSMap, []).
+
+:- func add_svar_unifier(svar_map, prog_context, svar, prog_var, hlds_goals)
+	= hlds_goals.
+
+add_svar_unifier(RHSMap, Context, StateVar, Var, Unifiers0) = Unifiers :-
+	( RHSVar = RHSMap ^ elem(StateVar) ->
+		Unifier = svar_unification(Context, Var, RHSVar),
+		Unifiers = [Unifier | Unifiers0]
+	;
+		Unifiers = Unifiers0
 	).
 
 %------------------------------------------------------------------------------%
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Index: tests/invalid/Mmakefile
===================================================================
RCS file: /home/mercury/mercury1/repository/tests/invalid/Mmakefile,v
retrieving revision 1.148
diff -u -b -r1.148 Mmakefile
--- tests/invalid/Mmakefile	20 Feb 2004 04:00:59 -0000	1.148
+++ tests/invalid/Mmakefile	6 Mar 2004 06:48:21 -0000
@@ -117,6 +117,7 @@
 	state_vars_test2 \
 	state_vars_test3 \
 	state_vars_test4 \
+	state_vars_test5 \
 	tc_err1 \
 	tc_err2 \
 	tricky_assert1 \
Index: tests/invalid/state_vars_test5.err_exp
===================================================================
RCS file: tests/invalid/state_vars_test5.err_exp
diff -N tests/invalid/state_vars_test5.err_exp
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ tests/invalid/state_vars_test5.err_exp	6 Mar 2004 06:47:54 -0000
@@ -0,0 +1,7 @@
+state_vars_test5.m:021: In clause for predicate `state_vars_test5.p/1':
+state_vars_test5.m:021:   warning: variable `STATE_VARIABLE_X' occurs only once in this scope.
+state_vars_test5.m:021: In clause for `p(out)':
+state_vars_test5.m:021:   mode error: argument 1 did not get sufficiently instantiated.
+state_vars_test5.m:021:   Final instantiatedness of `STATE_VARIABLE_X' was `free',
+state_vars_test5.m:021:   expected final instantiatedness was `ground'.
+For more information, try recompiling with `-E'.
Index: tests/invalid/state_vars_test5.m
===================================================================
RCS file: tests/invalid/state_vars_test5.m
diff -N tests/invalid/state_vars_test5.m
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ tests/invalid/state_vars_test5.m	6 Mar 2004 06:47:32 -0000
@@ -0,0 +1,21 @@
+%------------------------------------------------------------------------------%
+% vim: ft=mercury ff=unix ts=4 sw=4 et wm=0 tw=0
+%
+% This is a regression test. The versions of the compiler prior to 6 March 2004
+% used to get an exception inside the compiler code (in svar_unifiers in
+% make_hlds.m). This test checks that we get a meaningful error instead
+% of a compiler abort.
+%
+%------------------------------------------------------------------------------%
+
+:- module state_vars_test5.
+
+:- interface.
+
+:- import_module int.
+
+:- pred p(int::out) is det.
+
+:- implementation.
+
+p(!:X).
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