From c53d94e5127a8dcfefd906c5be0e6b81eaf3d22c Mon Sep 17 00:00:00 2001
From: LemonBoy <thatlemon@gmail.com>
Date: Sat, 18 Jan 2020 15:13:21 +0100
Subject: [PATCH 1/2] Prevent crash with empty non-exhaustive enum

---
 src/analyze.cpp               |  2 +-
 src/ir.cpp                    |  2 +-
 test/stage1/behavior/enum.zig | 20 ++++++++++++++++++++
 3 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/src/analyze.cpp b/src/analyze.cpp
index e064677a09..0bbec66a9b 100644
--- a/src/analyze.cpp
+++ b/src/analyze.cpp
@@ -8312,7 +8312,7 @@ static void resolve_llvm_types_enum(CodeGen *g, ZigType *enum_type, ResolveStatu
 
     uint32_t field_count = enum_type->data.enumeration.src_field_count;
 
-    assert(enum_type->data.enumeration.fields);
+    assert(field_count == 0 || enum_type->data.enumeration.fields != nullptr);
     ZigLLVMDIEnumerator **di_enumerators = allocate<ZigLLVMDIEnumerator*>(field_count);
 
     for (uint32_t i = 0; i < field_count; i += 1) {
diff --git a/src/ir.cpp b/src/ir.cpp
index 88b4c1a832..ae02ac9cae 100644
--- a/src/ir.cpp
+++ b/src/ir.cpp
@@ -21631,7 +21631,7 @@ static IrInstruction *ir_analyze_instruction_switch_target(IrAnalyze *ira,
         case ZigTypeIdEnum: {
             if ((err = type_resolve(ira->codegen, target_type, ResolveStatusZeroBitsKnown)))
                 return ira->codegen->invalid_instruction;
-            if (target_type->data.enumeration.src_field_count < 2) {
+            if (target_type->data.enumeration.src_field_count == 1) {
                 TypeEnumField *only_field = &target_type->data.enumeration.fields[0];
                 IrInstruction *result = ir_const(ira, &switch_target_instruction->base, target_type);
                 bigint_init_bigint(&result->value->data.x_enum_tag, &only_field->value);
diff --git a/test/stage1/behavior/enum.zig b/test/stage1/behavior/enum.zig
index 83ad76b72c..a478729003 100644
--- a/test/stage1/behavior/enum.zig
+++ b/test/stage1/behavior/enum.zig
@@ -65,6 +65,26 @@ test "non-exhaustive enum" {
     comptime S.doTheTest(52);
 }
 
+test "empty non-exhaustive enum" {
+    const S = struct {
+        const E = enum(u8) {
+            _,
+        };
+        fn doTheTest(y: u8) void {
+            var e = @intToEnum(E, y);
+            expect(switch (e) {
+                _ => true,
+            });
+            expect(@enumToInt(e) == y);
+
+            expect(@typeInfo(E).Enum.fields.len == 0);
+            expect(@typeInfo(E).Enum.is_exhaustive == false);
+        }
+    };
+    S.doTheTest(42);
+    comptime S.doTheTest(42);
+}
+
 test "enum type" {
     const foo1 = Foo{ .One = 13 };
     const foo2 = Foo{

From b0f753e21d6fcaafd0b35dc02fdfe23b14e310d6 Mon Sep 17 00:00:00 2001
From: LemonBoy <thatlemon@gmail.com>
Date: Sat, 18 Jan 2020 19:58:05 +0100
Subject: [PATCH 2/2] Fix edge case in tagName handling of unions

Closes #4226
---
 src/ir.cpp                     | 9 +++++++++
 test/stage1/behavior/union.zig | 9 +++++++++
 2 files changed, 18 insertions(+)

diff --git a/src/ir.cpp b/src/ir.cpp
index ae02ac9cae..ff4b552a9b 100644
--- a/src/ir.cpp
+++ b/src/ir.cpp
@@ -22354,6 +22354,15 @@ static IrInstruction *ir_analyze_instruction_enum_tag_name(IrAnalyze *ira, IrIns
 
     assert(target->value->type->id == ZigTypeIdEnum);
 
+    if (target->value->type->data.enumeration.src_field_count == 1 &&
+        !target->value->type->data.enumeration.non_exhaustive) {
+        TypeEnumField *only_field = &target->value->type->data.enumeration.fields[0];
+        ZigValue *array_val = create_const_str_lit(ira->codegen, only_field->name)->data.x_ptr.data.ref.pointee;
+        IrInstruction *result = ir_const(ira, &instruction->base, nullptr);
+        init_const_slice(ira->codegen, result->value, array_val, 0, buf_len(only_field->name), true);
+        return result;
+    }
+
     if (instr_is_comptime(target)) {
         if ((err = type_resolve(ira->codegen, target->value->type, ResolveStatusZeroBitsKnown)))
             return ira->codegen->invalid_instruction;
diff --git a/test/stage1/behavior/union.zig b/test/stage1/behavior/union.zig
index a24bee03e6..4625b7573a 100644
--- a/test/stage1/behavior/union.zig
+++ b/test/stage1/behavior/union.zig
@@ -629,3 +629,12 @@ test "union initializer generates padding only if needed" {
     var v = U{ .A = 532 };
     expect(v.A == 532);
 }
+
+test "runtime tag name with single field" {
+    const U = union(enum) {
+        A: i32,
+    };
+
+    var v = U{ .A = 42 };
+    expect(std.mem.eql(u8, @tagName(v), "A"));
+}