stage1: add a compile error for using @bitCast to convert an enum to an integer

lib/std/special/compiler_rt/compareXf2.zig

@@ -89,13 +89,13 @@ pub inline fn unordcmp(comptime T: type, a: T, b: T) i32 {
 pub fn __lesf2(a: f32, b: f32) callconv(.C) i32 {
     @setRuntimeSafety(builtin.is_test);
     const float = cmp(f32, LE, a, b);
-    return @bitCast(i32, float);
+    return @enumToInt(float);
 }
 
 pub fn __gesf2(a: f32, b: f32) callconv(.C) i32 {
     @setRuntimeSafety(builtin.is_test);
     const float = cmp(f32, GE, a, b);
-    return @bitCast(i32, float);
+    return @enumToInt(float);
 }
 
 pub fn __eqsf2(a: f32, b: f32) callconv(.C) i32 {
@@ -119,13 +119,13 @@ pub fn __gtsf2(a: f32, b: f32) callconv(.C) i32 {
 pub fn __ledf2(a: f64, b: f64) callconv(.C) i32 {
     @setRuntimeSafety(builtin.is_test);
     const float = cmp(f64, LE, a, b);
-    return @bitCast(i32, float);
+    return @enumToInt(float);
 }
 
 pub fn __gedf2(a: f64, b: f64) callconv(.C) i32 {
     @setRuntimeSafety(builtin.is_test);
     const float = cmp(f64, GE, a, b);
-    return @bitCast(i32, float);
+    return @enumToInt(float);
 }
 
 pub fn __eqdf2(a: f64, b: f64) callconv(.C) i32 {
@@ -149,13 +149,13 @@ pub fn __gtdf2(a: f64, b: f64) callconv(.C) i32 {
 pub fn __letf2(a: f128, b: f128) callconv(.C) i32 {
     @setRuntimeSafety(builtin.is_test);
     const float = cmp(f128, LE, a, b);
-    return @bitCast(i32, float);
+    return @enumToInt(float);
 }
 
 pub fn __getf2(a: f128, b: f128) callconv(.C) i32 {
     @setRuntimeSafety(builtin.is_test);
     const float = cmp(f128, GE, a, b);
-    return @bitCast(i32, float);
+    return @enumToInt(float);
 }
 
 pub fn __eqtf2(a: f128, b: f128) callconv(.C) i32 {

src/stage1/ir.cpp

@@ -12110,6 +12110,12 @@ static Stage1AirInst *ir_resolve_result_raw(IrAnalyze *ira, Stage1ZirInst *suspe
                 return ira->codegen->invalid_inst_gen;
             }
 
+            if (value_type->id == ZigTypeIdEnum && dest_type->id == ZigTypeIdInt) {
+                ir_add_error_node(ira, suspend_source_instr->source_node,
+                        buf_sprintf("@bitCast used instead of @enumToInt to convert an enum to an integer"));
+                return ira->codegen->invalid_inst_gen;
+            }
+
             Stage1AirInst *bitcasted_value;
             if (value != nullptr) {
                 bitcasted_value = ir_analyze_bit_cast(ira, result_loc->source_instruction->scope,

test/behavior/bitcast.zig

@@ -43,22 +43,6 @@ test "nested bitcast" {
     comptime try S.foo(42);
 }
 
-test "@bitCast enum to its integer type" {
-    const SOCK = enum(c_int) {
-        A,
-        B,
-
-        fn testBitCastExternEnum() !void {
-            var SOCK_DGRAM = @This().B;
-            var sock_dgram = @bitCast(c_int, SOCK_DGRAM);
-            try expect(sock_dgram == 1);
-        }
-    };
-
-    try SOCK.testBitCastExternEnum();
-    comptime try SOCK.testBitCastExternEnum();
-}
-
 // issue #3010: compiler segfault
 test "bitcast literal [4]u8 param to u32" {
     const ip = @bitCast(u32, [_]u8{ 255, 255, 255, 255 });

test/compile_errors.zig

@@ -1496,6 +1496,17 @@ pub fn addCases(ctx: *TestContext) !void {
         "tmp.zig:2:24: error: cannot cast a value of type 'y'",
     });
 
+    ctx.objErrStage1("bitCast enum to integer type",
+        \\export fn entry() void {
+        \\    const Number = enum(u32) { one, two };
+        \\    const x: Number = .one;
+        \\    const y = @bitCast(u32, x);
+        \\    _ = y;
+        \\}
+    , &[_][]const u8{
+        "tmp.zig:4:29: error: @bitCast used instead of @enumToInt to convert an enum to an integer",
+    });
+
     ctx.objErrStage1("comparing against undefined produces undefined value",
         \\export fn entry() void {
         \\    if (2 == undefined) {}