[m-rev.] diff: java switch on enums

[Peter Wang]

Branches: main

A recent change caused the MLDS backend to generate Java switch statements for
enumerations.  Mercury enumerations are represented by objects with an int
field, and neither the object nor the field are valid within case labels.
This fixes bug #209.

compiler/mlds_to_java.m:
	Write the integer value of the enumeration constant directly in case
	labels.

diff --git a/compiler/mlds_to_java.m b/compiler/mlds_to_java.m
index 686aff9..46d6166 100644
--- a/compiler/mlds_to_java.m
+++ b/compiler/mlds_to_java.m
@@ -4385,7 +4385,11 @@ output_case_cond(Info, Indent, Context, Match, !IO) :-
         Match = match_value(Val),
         indent_line(Info, Context, Indent, !IO),
         io.write_string("case ", !IO),
-        output_rval(Info, Val, !IO),
+        ( Val = ml_const(mlconst_enum(N, _)) ->
+            io.write_int(N, !IO)
+        ;
+            output_rval(Info, Val, !IO)
+        ),
         io.write_string(":\n", !IO)
     ;
         Match = match_range(_, _),

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