Commit e21ced91e30d8bc943ebe0a1f1f6d3bc6821740e | zig

author	Isaac Freund <mail@isaacfreund.com> 2026-06-15 17:09:59+02:00
committer	Isaac Freund <mail@isaacfreund.com> 2026-07-08 11:48:58+02:00
log	e21ced91e30d8bc943ebe0a1f1f6d3bc6821740e
tree	4655fd293313e5cab24cdefe7b95fc498f92a29a
parent	ac6930544f812582df10181210e80675ce6a42ee
signature	Commit is signed but in an unrecognized format.

std: move for loop capture count errors to AstGen

Currently Parse.zig gives a parse error when the number of for loop
inputs does not match the number of for loop captures. This property
is however both overly complex to specify in the formal grammar and not
necessary to make further parsing possible.

This eliminates yet another discrepancy between the formal grammar
and Parse.zig implementation that has been discovered through fuzzing
with AFL++.

4 files changed, 13 insertions(+), 21 deletions(-)

lib
- std
  - zig
    Ast.zig
    AstGen.zig
    Parse.zig
    parser_fuzz.zig

lib/std/zig/Ast.zig-8

 @@ -559,12 +559,6 @@ pub fn renderError(tree: Ast, parse_error: Error, w: *Writer) Writer.Error!void
         .var_const_decl => {
             return w.writeAll("use 'var' or 'const' to declare variable");
         },
-        .extra_for_capture => {
-            return w.writeAll("extra capture in for loop");
-        },
-        .for_input_not_captured => {
-            return w.writeAll("for input is not captured");
-        },
         .invalid_byte => {
             const tok_slice = tree.source[tree.tokens.items(.start)[parse_error.token]..];
 @@ -2889,8 +2883,6 @@ pub const Error = struct {
         expected_var_const,
         wrong_equal_var_decl,
         var_const_decl,
-        extra_for_capture,
-        for_input_not_captured,
         zig_style_container,
         previous_field,

lib/std/zig/AstGen.zig+7

 @@ -6708,6 +6708,9 @@ fn forExpr(
         for (for_full.ast.inputs, indexables, lens) |input, *indexable_ref, *len_refs| {
             const capture_is_ref = tree.tokenTag(capture_token) == .asterisk;
             const ident_tok = capture_token + @intFromBool(capture_is_ref);
+            if (tree.tokenTag(ident_tok) != .identifier) {
+                return astgen.failNode(input, "for input is not captured", .{});
+            }
             const is_discard = mem.eql(u8, tree.tokenSlice(ident_tok), "_");
             if (is_discard and capture_is_ref) {
 @@ -6750,6 +6753,10 @@ fn forExpr(
                 len_refs.* = .{ indexable, .none };
             }
         }
+        // There may or may not be a trailing comma after the final capture
+        if (tree.tokenTag(capture_token) != .pipe and tree.tokenTag(capture_token - 1) != .pipe) {
+            return astgen.failTok(capture_token, "extra capture in for loop", .{});
+        }
     }
     if (!any_len_checks) {

lib/std/zig/Parse.zig+1-13

 @@ -2106,16 +2106,9 @@ fn forPrefix(p: *Parse) Error!usize {
         return inputs;
     };
-    var warned_excess = false;
-    var captures: u32 = 0;
     while (true) {
         _ = p.eatToken(.asterisk);
-        const identifier = try p.expectToken(.identifier);
+        _ = try p.expectToken(.identifier);
-        captures += 1;
-        if (captures > inputs and !warned_excess) {
-            try p.warnMsg(.{ .tag = .extra_for_capture, .token = identifier });
-            warned_excess = true;
-        }
         switch (p.tokenTag(p.tok_i)) {
             .comma => p.tok_i += 1,
             .pipe => {
 @@ -2128,11 +2121,6 @@ fn forPrefix(p: *Parse) Error!usize {
         if (p.eatToken(.pipe)) |_| break;
     }
-    if (captures < inputs) {
-        const index = p.scratch.items.len - captures;
-        const input = p.nodeMainToken(p.scratch.items[index]);
-        try p.warnMsg(.{ .tag = .for_input_not_captured, .token = input });
-    }
     return inputs;
 }

lib/std/zig/parser_fuzz.zig+5

 @@ -52,6 +52,11 @@ test "newline required before doc comment not at start of file" {
     try checkAgainstOracle("///\ntest {}");
 }
+// Found using AFL++
+test "extra capture in for loop" {
+    try checkAgainstOracle("for(0)|t,r|0");
+}
 fn checkAgainstOracle(source: [:0]const u8) !void {
     var fba_buf: [1 << 18]u8 = undefined;
     var fba: std.heap.FixedBufferAllocator = .init(&fba_buf);