Prevent crash in tagged enums rendering (#1986)

* Prevent crash in tagged enums rendering

* Add a test case

src/analyze.cpp

@@ -6276,8 +6276,8 @@ void render_const_value(CodeGen *g, Buf *buf, ConstExprValue *const_val) {
             }
         case ZigTypeIdUnion:
             {
-                uint64_t tag = bigint_as_unsigned(&const_val->data.x_union.tag);
+                const BigInt *tag = &const_val->data.x_union.tag;
-                TypeUnionField *field = &type_entry->data.unionation.fields[tag];
+                TypeUnionField *field = find_union_field_by_tag(type_entry, tag);
                 buf_appendf(buf, "%s { .%s = ", buf_ptr(&type_entry->name), buf_ptr(field->name));
                 render_const_value(g, buf, const_val->data.x_union.payload);
                 buf_append_str(buf, "}");

test/compile_errors.zig

@@ -5599,4 +5599,21 @@ pub fn addCases(cases: *tests.CompileErrorContext) void {
     ,
         ".tmp_source.zig:2:26: error: vector element type must be integer, float, or pointer; '@Vector(4, u8)' is invalid",
     );
+
+    cases.add(
+        "compileLog of tagged enum doesn't crash the compiler",
+        \\const Bar = union(enum(u32)) {
+        \\    X: i32 = 1
+        \\};
+        \\
+        \\fn testCompileLog(x: Bar) void {
+        \\    @compileLog(x);
+        \\}
+        \\
+        \\pub fn main () void {
+        \\    comptime testCompileLog(Bar{.X = 123});
+        \\}
+    ,
+        ".tmp_source.zig:6:5: error: found compile log statement"
+    );
 }