Fix incorrect detection of exhaustive matches for structural equality comparisons on some primitives.

src/libponyc/expr/match.c

@@ -111,7 +111,7 @@ static ast_t* is_match_exhaustive(pass_opt_t* opt, ast_t* expr_type,
   for(ast_t* c = ast_child(cases); c != NULL; c = ast_sibling(c))
   {
     AST_GET_CHILDREN(c, case_expr, guard, case_body);
-    ast_t* pattern_type = ast_type(c);
+    ast_t* case_type = ast_type(case_expr);
 
     // if any case is a `_` we have an exhaustive match
     // and we can shortcut here
@@ -133,7 +133,7 @@ static ast_t* is_match_exhaustive(pass_opt_t* opt, ast_t* expr_type,
       continue;
 
     // It counts, so add this pattern type to our running union type.
-    ast_add(cases_union_type, pattern_type);
+    ast_add(cases_union_type, case_type);
 
     // If our cases types union is a supertype of the match expression type,
     // then the match must be exhaustive, because all types are covered by cases.

test/libponyc/sugar_expr.cc

@@ -972,6 +972,49 @@ TEST_F(SugarExprTest, MatchExhaustiveUnreachableCases)
   TEST_ERRORS_1(src, "match contains unreachable cases");
 }
 
+TEST_F(SugarExprTest, MatchExhaustiveEquatableOfSubType)
+{
+  const char* src =
+    "interface Equatable[T]\n"
+    "  fun eq(that: T): Bool => this is that\n"
+    "primitive X is Equatable[Dimension]\n"
+    "primitive Y is Equatable[Dimension]\n"
+    "primitive Z is Equatable[Dimension]\n"
+    "\n"
+    "type Dimension is ( X | Y | Z )\n"
+    "\n"
+    "primitive Foo\n"
+    "  fun apply(p: Dimension) =>\n"
+    "    let s: String =\n"
+    "      match p\n"
+    "      | X => \"x\"\n"
+    "      | Y => \"y\"\n"
+    "      | Z => \"z\"\n"
+    "      end";
+  TEST_COMPILE(src);
+}
+
+TEST_F(SugarExprTest, MatchNonExhaustiveSubsetOfEquatableOfSubType)
+{
+  const char* src =
+    "interface Equatable[T]\n"
+    "  fun eq(that: T): Bool => this is that\n"
+    "primitive X is Equatable[Dimension]\n"
+    "primitive Y is Equatable[Dimension]\n"
+    "primitive Z is Equatable[Dimension]\n"
+    "\n"
+    "type Dimension is ( X | Y | Z )\n"
+    "\n"
+    "primitive Foo\n"
+    "  fun apply(p: Dimension): String =>\n"
+    "      match p\n"
+    "      | X => \"x\"\n"
+    "      | Y => \"y\"\n"
+    "      end";
+  TEST_ERRORS_1(src, "function body isn't the result type");
+
+}
+
 TEST_F(SugarExprTest, MatchStructuralEqualityOnIncompatibleUnion)
 {
   // From issue #2110