Merge pull request #15591 from jacobly0/undef-errdefer-capture

AstGen: fix branch on undefined

src/AstGen.zig

@@ -2905,7 +2905,15 @@ fn deferStmt(
     const sub_scope = if (!have_err_code) &defer_gen.base else blk: {
         try gz.addDbgBlockBegin();
         const ident_name = try gz.astgen.identAsString(payload_token);
-        remapped_err_code = @intCast(u32, try gz.astgen.instructions.addOne(gz.astgen.gpa));
+        remapped_err_code = @intCast(Zir.Inst.Index, gz.astgen.instructions.len);
+        try gz.astgen.instructions.append(gz.astgen.gpa, .{
+            .tag = .extended,
+            .data = .{ .extended = .{
+                .opcode = .errdefer_err_code,
+                .small = undefined,
+                .operand = undefined,
+            } },
+        });
         const remapped_err_code_ref = Zir.indexToRef(remapped_err_code);
         local_val_scope = .{
             .parent = &defer_gen.base,

src/Sema.zig

@@ -1198,6 +1198,7 @@ fn analyzeBodyInner(
                         i += 1;
                         continue;
                     },
+                    .errdefer_err_code => unreachable, // never appears in a body
                 };
             },
 

src/Zir.zig

@@ -1979,7 +1979,7 @@ pub const Inst = struct {
         /// `operand` is `src_node: i32`.
         breakpoint,
         /// Implements the `@select` builtin.
-        /// operand` is payload index to `Select`.
+        /// `operand` is payload index to `Select`.
         select,
         /// Implement builtin `@errToInt`.
         /// `operand` is payload index to `UnNode`.
@@ -1999,7 +1999,7 @@ pub const Inst = struct {
         /// `operand` is payload index to `Cmpxchg`.
         cmpxchg,
         /// Implement the builtin `@addrSpaceCast`
-        /// `Operand` is payload index to `BinNode`. `lhs` is dest type, `rhs` is operand.
+        /// `operand` is payload index to `BinNode`. `lhs` is dest type, `rhs` is operand.
         addrspace_cast,
         /// Implement builtin `@cVaArg`.
         /// `operand` is payload index to `BinNode`.
@@ -2031,6 +2031,9 @@ pub const Inst = struct {
         /// Implements the `@inComptime` builtin.
         /// `operand` is `src_node: i32`.
         in_comptime,
+        /// Used as a placeholder for the capture of an `errdefer`.
+        /// This is replaced by Sema with the captured value.
+        errdefer_err_code,
 
         pub const InstData = struct {
             opcode: Extended,

src/print_zir.zig

@@ -467,6 +467,7 @@ const Writer = struct {
             .breakpoint,
             .c_va_start,
             .in_comptime,
+            .errdefer_err_code,
             => try self.writeExtNode(stream, extended),
 
             .builtin_src => {