Sema: improve safety panic for access of inactive union field

4 files changed, 45 insertions, 83 deletions

diff --git a/doc/langref.html.in b/doc/langref.html.in
index 8974ab06cf..dcb15af9f6 100644
--- a/doc/langref.html.in
+++ b/doc/langref.html.in
@@ -3803,7 +3803,7 @@ test "switch on non-exhaustive enum" {
       {#link|Accessing the non-active field|Wrong Union Field Access#} is
       safety-checked {#link|Undefined Behavior#}:
       </p>
-      {#code_begin|test_err|inactive union field#}
+      {#code_begin|test_err|access of union field 'float' while field 'int' is active#}
 const Payload = union {
     int: i64,
     float: f64,
diff --git a/lib/std/builtin.zig b/lib/std/builtin.zig
index 09833988ae..fcdf43bd31 100644
--- a/lib/std/builtin.zig
+++ b/lib/std/builtin.zig
@@ -868,6 +868,11 @@ pub fn panicStartGreaterThanEnd(start: usize, end: usize) noreturn {
     std.debug.panicExtra(null, @returnAddress(), "start index {d} is larger than end index {d}", .{ start, end });
 }
 
+pub fn panicInactiveUnionField(active: anytype, wanted: @TypeOf(active)) noreturn {
+    @setCold(true);
+    std.debug.panicExtra(null, @returnAddress(), "access of union field '{s}' while field '{s}' is active", .{ @tagName(wanted), @tagName(active) });
+}
+
 pub const panic_messages = struct {
     pub const unreach = "reached unreachable code";
     pub const unwrap_null = "attempt to use null value";
diff --git a/src/Sema.zig b/src/Sema.zig
index d35c4e3881..396c5912fa 100644
--- a/src/Sema.zig
+++ b/src/Sema.zig
@@ -22120,7 +22120,6 @@ pub const PanicId = enum {
     shr_overflow,
     divide_by_zero,
     exact_division_remainder,
-    /// TODO make this call `std.builtin.panicInactiveUnionField`.
     inactive_union_field,
     integer_part_out_of_bounds,
     corrupt_switch,
@@ -22296,90 +22295,40 @@ fn panicUnwrapError(
 fn panicIndexOutOfBounds(
     sema: *Sema,
     parent_block: *Block,
-    src: LazySrcLoc,
     index: Air.Inst.Ref,
     len: Air.Inst.Ref,
     cmp_op: Air.Inst.Tag,
 ) !void {
     assert(!parent_block.is_comptime);
     const ok = try parent_block.addBinOp(cmp_op, index, len);
-    const gpa = sema.gpa;
-
-    var fail_block: Block = .{
-        .parent = parent_block,
-        .sema = sema,
-        .src_decl = parent_block.src_decl,
-        .namespace = parent_block.namespace,
-        .wip_capture_scope = parent_block.wip_capture_scope,
-        .instructions = .{},
-        .inlining = parent_block.inlining,
-        .is_comptime = false,
-    };
-
-    defer fail_block.instructions.deinit(gpa);
-
-    {
-        const this_feature_is_implemented_in_the_backend =
-            sema.mod.comp.bin_file.options.use_llvm;
-
-        if (!this_feature_is_implemented_in_the_backend) {
-            // TODO implement this feature in all the backends and then delete this branch
-            _ = try fail_block.addNoOp(.breakpoint);
-            _ = try fail_block.addNoOp(.unreach);
-        } else {
-            const panic_fn = try sema.getBuiltin("panicOutOfBounds");
-            const args: [2]Air.Inst.Ref = .{ index, len };
-            _ = try sema.analyzeCall(&fail_block, panic_fn, src, src, .auto, false, &args, null);
-        }
-    }
-    try sema.addSafetyCheckExtra(parent_block, ok, &fail_block);
+    try sema.safetyPanicFormatted(parent_block, ok, "panicOutOfBounds", &.{ index, len });
 }
 
 fn panicStartLargerThanEnd(
     sema: *Sema,
     parent_block: *Block,
-    src: LazySrcLoc,
     start: Air.Inst.Ref,
     end: Air.Inst.Ref,
 ) !void {
     assert(!parent_block.is_comptime);
     const ok = try parent_block.addBinOp(.cmp_lte, start, end);
-    const gpa = sema.gpa;
-
-    var fail_block: Block = .{
-        .parent = parent_block,
-        .sema = sema,
-        .src_decl = parent_block.src_decl,
-        .namespace = parent_block.namespace,
-        .wip_capture_scope = parent_block.wip_capture_scope,
-        .instructions = .{},
-        .inlining = parent_block.inlining,
-        .is_comptime = false,
-    };
-
-    defer fail_block.instructions.deinit(gpa);
-
-    {
-        const this_feature_is_implemented_in_the_backend =
-            sema.mod.comp.bin_file.options.use_llvm;
+    try sema.safetyPanicFormatted(parent_block, ok, "panicStartGreaterThanEnd", &.{ start, end });
+}
 
-        if (!this_feature_is_implemented_in_the_backend) {
-            // TODO implement this feature in all the backends and then delete this branch
-            _ = try fail_block.addNoOp(.breakpoint);
-            _ = try fail_block.addNoOp(.unreach);
-        } else {
-            const panic_fn = try sema.getBuiltin("panicStartGreaterThanEnd");
-            const args: [2]Air.Inst.Ref = .{ start, end };
-            _ = try sema.analyzeCall(&fail_block, panic_fn, src, src, .auto, false, &args, null);
-        }
-    }
-    try sema.addSafetyCheckExtra(parent_block, ok, &fail_block);
+fn panicInactiveUnionField(
+    sema: *Sema,
+    parent_block: *Block,
+    active_tag: Air.Inst.Ref,
+    wanted_tag: Air.Inst.Ref,
+) !void {
+    assert(!parent_block.is_comptime);
+    const ok = try parent_block.addBinOp(.cmp_eq, active_tag, wanted_tag);
+    try sema.safetyPanicFormatted(parent_block, ok, "panicInactiveUnionField", &.{ active_tag, wanted_tag });
 }
 
 fn panicSentinelMismatch(
     sema: *Sema,
     parent_block: *Block,
-    src: LazySrcLoc,
     maybe_sentinel: ?Value,
     sentinel_ty: Type,
     ptr: Air.Inst.Ref,
@@ -22413,9 +22362,20 @@ fn panicSentinelMismatch(
     else {
         const panic_fn = try sema.getBuiltin("checkNonScalarSentinel");
         const args: [2]Air.Inst.Ref = .{ expected_sentinel, actual_sentinel };
-        _ = try sema.analyzeCall(parent_block, panic_fn, src, src, .auto, false, &args, null);
+        _ = try sema.analyzeCall(parent_block, panic_fn, sema.src, sema.src, .auto, false, &args, null);
         return;
     };
+
+    try sema.safetyPanicFormatted(parent_block, ok, "panicSentinelMismatch", &.{ expected_sentinel, actual_sentinel });
+}
+
+fn safetyPanicFormatted(
+    sema: *Sema,
+    parent_block: *Block,
+    ok: Air.Inst.Ref,
+    func: []const u8,
+    args: []const Air.Inst.Ref,
+) CompileError!void {
     const gpa = sema.gpa;
 
     var fail_block: Block = .{
@@ -22440,9 +22400,8 @@ fn panicSentinelMismatch(
             _ = try fail_block.addNoOp(.breakpoint);
             _ = try fail_block.addNoOp(.unreach);
         } else {
-            const panic_fn = try sema.getBuiltin("panicSentinelMismatch");
-            const args: [2]Air.Inst.Ref = .{ expected_sentinel, actual_sentinel };
-            _ = try sema.analyzeCall(&fail_block, panic_fn, src, src, .auto, false, &args, null);
+            const panic_fn = try sema.getBuiltin(func);
+            _ = try sema.analyzeCall(&fail_block, panic_fn, sema.src, sema.src, .auto, false, args, null);
         }
     }
     try sema.addSafetyCheckExtra(parent_block, ok, &fail_block);
@@ -23465,8 +23424,7 @@ fn unionFieldPtr(
         // TODO would it be better if get_union_tag supported pointers to unions?
         const union_val = try block.addTyOp(.load, union_ty, union_ptr);
         const active_tag = try block.addTyOp(.get_union_tag, union_obj.tag_ty, union_val);
-        const ok = try block.addBinOp(.cmp_eq, active_tag, wanted_tag);
-        try sema.addSafetyCheck(block, ok, .inactive_union_field);
+        try sema.panicInactiveUnionField(block, active_tag, wanted_tag);
     }
     if (field.ty.zigTypeTag() == .NoReturn) {
         _ = try block.addNoOp(.unreach);
@@ -23537,8 +23495,7 @@ fn unionFieldVal(
         const wanted_tag_val = try Value.Tag.enum_field_index.create(sema.arena, enum_field_index);
         const wanted_tag = try sema.addConstant(union_obj.tag_ty, wanted_tag_val);
         const active_tag = try block.addTyOp(.get_union_tag, union_obj.tag_ty, union_byval);
-        const ok = try block.addBinOp(.cmp_eq, active_tag, wanted_tag);
-        try sema.addSafetyCheck(block, ok, .inactive_union_field);
+        try sema.panicInactiveUnionField(block, active_tag, wanted_tag);
     }
     if (field.ty.zigTypeTag() == .NoReturn) {
         _ = try block.addNoOp(.unreach);
@@ -23849,7 +23806,7 @@ fn elemValArray(
         if (maybe_index_val == null) {
             const len_inst = try sema.addIntUnsigned(Type.usize, array_len);
             const cmp_op: Air.Inst.Tag = if (array_sent != null) .cmp_lte else .cmp_lt;
-            try sema.panicIndexOutOfBounds(block, elem_index_src, elem_index, len_inst, cmp_op);
+            try sema.panicIndexOutOfBounds(block, elem_index, len_inst, cmp_op);
         }
     }
     return block.addBinOp(.array_elem_val, array, elem_index);
@@ -23910,7 +23867,7 @@ fn elemPtrArray(
     if (block.wantSafety() and offset == null) {
         const len_inst = try sema.addIntUnsigned(Type.usize, array_len);
         const cmp_op: Air.Inst.Tag = if (array_sent) .cmp_lte else .cmp_lt;
-        try sema.panicIndexOutOfBounds(block, elem_index_src, elem_index, len_inst, cmp_op);
+        try sema.panicIndexOutOfBounds(block, elem_index, len_inst, cmp_op);
     }
 
     return block.addPtrElemPtr(array_ptr, elem_index, elem_ptr_ty);
@@ -23966,7 +23923,7 @@ fn elemValSlice(
         else
             try block.addTyOp(.slice_len, Type.usize, slice);
         const cmp_op: Air.Inst.Tag = if (slice_sent) .cmp_lte else .cmp_lt;
-        try sema.panicIndexOutOfBounds(block, elem_index_src, elem_index, len_inst, cmp_op);
+        try sema.panicIndexOutOfBounds(block, elem_index, len_inst, cmp_op);
     }
     try sema.queueFullTypeResolution(sema.typeOf(slice));
     return block.addBinOp(.slice_elem_val, slice, elem_index);
@@ -24025,7 +23982,7 @@ fn elemPtrSlice(
             break :len try block.addTyOp(.slice_len, Type.usize, slice);
         };
         const cmp_op: Air.Inst.Tag = if (slice_sent) .cmp_lte else .cmp_lt;
-        try sema.panicIndexOutOfBounds(block, elem_index_src, elem_index, len_inst, cmp_op);
+        try sema.panicIndexOutOfBounds(block, elem_index, len_inst, cmp_op);
     }
     return block.addSliceElemPtr(slice, elem_index, elem_ptr_ty);
 }
@@ -28072,7 +28029,7 @@ fn analyzeSlice(
 
     if (block.wantSafety() and !block.is_comptime) {
         // requirement: start <= end
-        try sema.panicStartLargerThanEnd(block, src, start, end);
+        try sema.panicStartLargerThanEnd(block, start, end);
     }
     const new_len = try sema.analyzeArithmetic(block, .sub, end, start, src, end_src, start_src, false);
     const opt_new_len_val = try sema.resolveDefinedValue(block, src, new_len);
@@ -28116,11 +28073,11 @@ fn analyzeSlice(
                     else
                         end;
 
-                    try sema.panicIndexOutOfBounds(block, src, actual_end, actual_len, .cmp_lte);
+                    try sema.panicIndexOutOfBounds(block, actual_end, actual_len, .cmp_lte);
                 }
 
                 // requirement: result[new_len] == slice_sentinel
-                try sema.panicSentinelMismatch(block, src, slice_sentinel, elem_ty, result, new_len);
+                try sema.panicSentinelMismatch(block, slice_sentinel, elem_ty, result, new_len);
             }
             return result;
         };
@@ -28184,11 +28141,11 @@ fn analyzeSlice(
                 try sema.analyzeArithmetic(block, .add, end, .one, src, end_src, end_src, true)
             else
                 end;
-            try sema.panicIndexOutOfBounds(block, src, actual_end, len_inst, .cmp_lte);
+            try sema.panicIndexOutOfBounds(block, actual_end, len_inst, .cmp_lte);
         }
 
         // requirement: start <= end
-        try sema.panicIndexOutOfBounds(block, src, start, end, .cmp_lte);
+        try sema.panicIndexOutOfBounds(block, start, end, .cmp_lte);
     }
     const result = try block.addInst(.{
         .tag = .slice,
@@ -28202,7 +28159,7 @@ fn analyzeSlice(
     });
     if (block.wantSafety()) {
         // requirement: result[new_len] == slice_sentinel
-        try sema.panicSentinelMismatch(block, src, slice_sentinel, elem_ty, result, new_len);
+        try sema.panicSentinelMismatch(block, slice_sentinel, elem_ty, result, new_len);
     }
     return result;
 }
diff --git a/test/cases/safety/bad union field access.zig b/test/cases/safety/bad union field access.zig
index 0badf380fb..fbe7718c66 100644
--- a/test/cases/safety/bad union field access.zig
+++ b/test/cases/safety/bad union field access.zig
@@ -2,7 +2,7 @@ const std = @import("std");
 
 pub fn panic(message: []const u8, stack_trace: ?*std.builtin.StackTrace, _: ?usize) noreturn {
     _ = stack_trace;
-    if (std.mem.eql(u8, message, "access of inactive union field")) {
+    if (std.mem.eql(u8, message, "access of union field 'float' while field 'int' is active")) {
         std.process.exit(0);
     }
     std.process.exit(1);