From c577aa7a2e2e1db245d20ca6ae23e4d630c51897 Mon Sep 17 00:00:00 2001
From: Taylan Kammer <taylan.kammer@gmail.com>
Date: Tue, 23 Jun 2026 18:15:04 +0200
Subject: Don't alloc or decode for datum comments.

---
 src/zisp/io/Parser.zig | 28 +++++++++++++++++++++-------
 1 file changed, 21 insertions(+), 7 deletions(-)

diff --git a/src/zisp/io/Parser.zig b/src/zisp/io/Parser.zig
index 6e9f87e..1b3808a 100644
--- a/src/zisp/io/Parser.zig
+++ b/src/zisp/io/Parser.zig
@@ -104,6 +104,7 @@ decoder: ?*Decoder,
 
 reader: *Reader = undefined,
 context: Context = .{},
+comment: bool = false,
 result: Value = undefined,
 unread_char: ?u8 = null,
 err_msg: []const u8 = undefined,
@@ -194,10 +195,12 @@ fn getUnread(p: *Parser) ?u8 {
 //
 
 fn addChar(p: *Parser, c: u8) !void {
+    if (p.comment) return;
     try p.str_chars.append(p.alloc, c);
 }
 
 fn addUnicode(p: *Parser, uc: u21) !void {
+    if (p.comment) return;
     const n = std.unicode.utf8CodepointSequenceLength(uc) catch {
         return p.err(.UnicodeLengthError, "Unicode/UTF-8 escape");
     };
@@ -238,10 +241,12 @@ fn getCharsAsRune(p: *Parser) Value {
 //
 
 fn addListElt(p: *Parser, elt: Value) !void {
+    if (p.comment) return;
     try p.list_elts.append(p.alloc, elt);
 }
 
 fn getList(p: *Parser) !Value {
+    if (p.comment) return value.nil;
     if (p.list_elts.items.len == p.context.list_start) return value.nil;
     defer p.list_elts.items.len = p.context.list_start;
     const vals = p.list_elts.items[p.context.list_start..];
@@ -259,6 +264,7 @@ fn makeList(p: *Parser, vals: []const Value) !Value {
 const Fn = enum {
     parseUnit,
     endUnit,
+    endSkipUnit,
     returnContext,
     parseDatum,
     endDatum,
@@ -275,6 +281,7 @@ inline fn call(p: *Parser, f: Fn) !void {
     try switch (f) {
         .parseUnit => p.parseUnit(),
         .endUnit => p.endUnit(),
+        .endSkipUnit => p.endSkipUnit(),
         .returnContext => p.returnContext(),
         .parseDatum => p.parseDatum(),
         .endDatum => p.endDatum(),
@@ -380,6 +387,7 @@ fn retNoDecode(p: *Parser, val: Value) void {
 }
 
 fn decode(p: *Parser, val: Value) !Value {
+    if (p.comment) return val;
     if (p.decoder) |dec| return dec.decodeInPlace(val);
     return val;
 }
@@ -393,12 +401,7 @@ fn parseUnit(p: *Parser) !void {
     while (c1) |c| : (c1 = try p.read()) {
         switch (try p.checkBlank(c)) {
             .yes => {},
-            .skip_unit => {
-                // Queue another parseUnit, but continue the current one, whose
-                // result will be silently ignored.  Simpler alternative to:
-                // return p.subr(.parseUnit, .parseUnit);
-                try p.push(.parseUnit);
-            },
+            .skip_unit => return p.skipUnit(.parseUnit),
             .no => {
                 p.unread(c);
                 return p.subr(.parseDatum, .endUnit);
@@ -408,13 +411,24 @@ fn parseUnit(p: *Parser) !void {
     return p.retval(value.eof);
 }
 
+fn skipUnit(p: *Parser, next: Fn) !void {
+    p.comment = true;
+    try p.push(next);
+    return p.subr(.parseUnit, .endSkipUnit);
+}
+
+fn endSkipUnit(p: *Parser) !void {
+    p.comment = false;
+    return p.ret();
+}
+
 fn endUnit(p: *Parser) !void {
     const c = p.getUnread() orelse return p.ret();
     switch (try p.checkBlank(c)) {
         .yes => {},
         .skip_unit => {
             p.context.val = p.result;
-            return p.subr(.parseUnit, .returnContext);
+            return p.skipUnit(.returnContext);
         },
         .no => p.unread(c),
     }
-- 
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