From 2948f2d262926725b4b8cb5beeb4fdba00b48336 Mon Sep 17 00:00:00 2001
From: Vexu <git@vexu.eu>
Date: Mon, 27 Jul 2020 18:42:13 +0300
Subject: [PATCH] fix cast from invalid non-exhaustive enum to union

---
 src/ir.cpp              | 16 +++++++++++++++-
 test/compile_errors.zig | 23 +++++++++++++++++++++++
 2 files changed, 38 insertions(+), 1 deletion(-)

diff --git a/src/ir.cpp b/src/ir.cpp
index 347cae7e79..209dd6d7d0 100644
--- a/src/ir.cpp
+++ b/src/ir.cpp
@@ -14177,7 +14177,14 @@ static IrInstGen *ir_analyze_enum_to_union(IrAnalyze *ira, IrInst* source_instr,
         if (!val)
             return ira->codegen->invalid_inst_gen;
         TypeUnionField *union_field = find_union_field_by_tag(wanted_type, &val->data.x_enum_tag);
-        assert(union_field != nullptr);
+        if (union_field == nullptr) {
+            Buf *int_buf = buf_alloc();
+            bigint_append_buf(int_buf, &target->value->data.x_enum_tag, 10);
+
+            ir_add_error(ira, &target->base,
+                buf_sprintf("no tag by value %s", buf_ptr(int_buf)));
+            return ira->codegen->invalid_inst_gen;
+        }
         ZigType *field_type = resolve_union_field_type(ira->codegen, union_field);
         if (field_type == nullptr)
             return ira->codegen->invalid_inst_gen;
@@ -14213,6 +14220,13 @@ static IrInstGen *ir_analyze_enum_to_union(IrAnalyze *ira, IrInst* source_instr,
         return result;
     }
 
+    if (target->value->type->data.enumeration.non_exhaustive) {
+        ir_add_error(ira, source_instr,
+                buf_sprintf("runtime cast to union '%s' from non-exhustive enum",
+                    buf_ptr(&wanted_type->name)));
+        return ira->codegen->invalid_inst_gen;
+    }
+
     // if the union has all fields 0 bits, we can do it
     // and in fact it's a noop cast because the union value is just the enum value
     if (wanted_type->data.unionation.gen_field_count == 0) {
diff --git a/test/compile_errors.zig b/test/compile_errors.zig
index 6c123925da..0b9c754329 100644
--- a/test/compile_errors.zig
+++ b/test/compile_errors.zig
@@ -51,6 +51,29 @@ pub fn addCases(cases: *tests.CompileErrorContext) void {
         "tmp.zig:17:23: error: cannot adjust alignment of zero sized type 'fn(u32) anytype'",
     });
 
+    cases.addTest("invalid non-exhaustive enum to union",
+        \\const E = enum(u8) {
+        \\    a,
+        \\    b,
+        \\    _,
+        \\};
+        \\const U = union(E) {
+        \\    a,
+        \\    b,
+        \\};
+        \\export fn foo() void {
+        \\    var e = @intToEnum(E, 15);
+        \\    var u: U = e;
+        \\}
+        \\export fn bar() void {
+        \\    const e = @intToEnum(E, 15);
+        \\    var u: U = e;
+        \\}
+    , &[_][]const u8{
+        "tmp.zig:12:16: error: runtime cast to union 'U' from non-exhustive enum",
+        "tmp.zig:16:16: error: no tag by value 15",
+    });
+
     cases.addTest("switching with exhaustive enum has '_' prong ",
         \\const E = enum{
         \\    a,