From fe44dffa12470397146d079445ea4409961e734b Mon Sep 17 00:00:00 2001
From: Isaac Freund <mail@isaacfreund.com>
Date: Tue, 7 Jul 2026 14:22:17 +0200
Subject: [PATCH] grammar: eliminate ContainerField backtracking

For in depth reasoning, see commit 296b39c32324
(grammar: fix ParamDeclList worst-case exponential time)
---
 doc/langref/grammar.peg                 |  7 +--
 lib/std/zig/parser_generated_oracle.zig | 57 +++++++++++--------------
 2 files changed, 28 insertions(+), 36 deletions(-)

diff --git a/doc/langref/grammar.peg b/doc/langref/grammar.peg
index d78765560e548dec404fb1378952ef9a42a65676..bce5b0b94ad32be346c1d95cf6c5698df149897e 100644
--- a/doc/langref/grammar.peg
+++ b/doc/langref/grammar.peg
@@ -39,9 +39,10 @@
 Root <- ContainerMembers skip eof
 
 # *** Top level ***
-ContainerMembers <- container_doc_comment? ContainerDecl* !ContainerDeclPrefix
-                    (!ContainerDeclPrefix ContainerField COMMA)*
-                    (!ContainerDeclPrefix ContainerField / ContainerDecl*)
+ContainerMembers <- container_doc_comment? ContainerDecl* ContainerMembersRest
+ContainerMembersRest
+    <- !ContainerDeclPrefix ContainerField (COMMA ContainerMembersRest)?
+     / ContainerDecl*
 
 ContainerDecl <- TestDecl / ComptimeDecl / doc_comment? KEYWORD_pub? Decl
 
diff --git a/lib/std/zig/parser_generated_oracle.zig b/lib/std/zig/parser_generated_oracle.zig
index 667c061d24b0e309c5c59fedb21115da5e63bda2..8327c715200d450cdf8ee8da8ec60be054d82ca9 100644
--- a/lib/std/zig/parser_generated_oracle.zig
+++ b/lib/std/zig/parser_generated_oracle.zig
@@ -16,6 +16,7 @@ pub fn parse(source: []const u8) Error!bool {
 const Def = enum {
     defRoot,
     defContainerMembers,
+    defContainerMembersRest,
     defContainerDecl,
     defContainerDeclPrefix,
     defTestDecl,
@@ -289,7 +290,7 @@ const Def = enum {
 const Parser = struct {
     source: []const u8,
     i: usize,
-    depths: [271]u8,
+    depths: [272]u8,
     pub fn parseRoot(p: *Parser) Error!bool {
         const def_index = @intFromEnum(Def.defRoot);
         if (p.depths[def_index] > max_depth) return error.MaxDepth;
@@ -316,47 +317,37 @@ const Parser = struct {
                     i_1 += 1;
                 }
                 break :blk_1 true;
-            } and blk_1: {
+            } and try p.parseContainerMembersRest()) break :blk_0 true;
+            p.i = pos_0;
+            break :blk_0 false;
+        };
+    }
+    pub fn parseContainerMembersRest(p: *Parser) Error!bool {
+        const def_index = @intFromEnum(Def.defContainerMembersRest);
+        if (p.depths[def_index] > max_depth) return error.MaxDepth;
+        p.depths[def_index] += 1;
+        defer p.depths[def_index] -= 1;
+        return blk_0: {
+            const pos_0 = p.i;
+            if (blk_1: {
                 const pos_1 = p.i;
                 const match_1 = try p.parseContainerDeclPrefix();
                 p.i = pos_1;
                 break :blk_1 !match_1;
-            } and blk_1: {
+            } and try p.parseContainerField() and (blk_3: {
+                const pos_3 = p.i;
+                if (try p.parseCOMMA() and try p.parseContainerMembersRest()) break :blk_3 true;
+                p.i = pos_3;
+                break :blk_3 false;
+            } or true)) break :blk_0 true;
+            p.i = pos_0;
+            if (blk_1: {
                 var i_1: usize = 0;
-                while (blk_3: {
-                    const pos_3 = p.i;
-                    if (blk_4: {
-                        const pos_4 = p.i;
-                        const match_4 = try p.parseContainerDeclPrefix();
-                        p.i = pos_4;
-                        break :blk_4 !match_4;
-                    } and try p.parseContainerField() and try p.parseCOMMA()) break :blk_3 true;
-                    p.i = pos_3;
-                    break :blk_3 false;
-                }) {
+                while (try p.parseContainerDecl()) {
                     if (i_1 > max_depth) return error.MaxDepth;
                     i_1 += 1;
                 }
                 break :blk_1 true;
-            } and blk_2: {
-                const pos_2 = p.i;
-                if (blk_3: {
-                    const pos_3 = p.i;
-                    const match_3 = try p.parseContainerDeclPrefix();
-                    p.i = pos_3;
-                    break :blk_3 !match_3;
-                } and try p.parseContainerField()) break :blk_2 true;
-                p.i = pos_2;
-                if (blk_3: {
-                    var i_3: usize = 0;
-                    while (try p.parseContainerDecl()) {
-                        if (i_3 > max_depth) return error.MaxDepth;
-                        i_3 += 1;
-                    }
-                    break :blk_3 true;
-                }) break :blk_2 true;
-                p.i = pos_2;
-                break :blk_2 false;
             }) break :blk_0 true;
             p.i = pos_0;
             break :blk_0 false;
-- 
2.54.0