yuku-toolchain
diff --git a/‎src/parser/parser.zig‎
Lines changed: 3 additions & 0 deletions b/‎src/parser/parser.zig‎
Lines changed: 3 additions & 0 deletions
diff --git a/‎src/parser/syntax/ts/arrows.zig‎
Lines changed: 4 additions & 0 deletions b/‎src/parser/syntax/ts/arrows.zig‎
Lines changed: 4 additions & 0 deletions
diff --git a/‎src/parser/syntax/ts/types/core.zig‎
Lines changed: 8 additions & 3 deletions b/‎src/parser/syntax/ts/types/core.zig‎
Lines changed: 8 additions & 3 deletions
@@ -105,6 +105,9 @@ pub const Parser = struct {
     ts_context: TsContext = .{},
     state: ParserState = .{},
 
+    // token offsets whose speculation failed, so a rewinding ancestor never re-parses them
+    ts_rejected_speculations: std.AutoHashMapUnmanaged(u32, void) = .empty,
+
     pub fn init(child_allocator: std.mem.Allocator, source: []const u8, options: Options) Parser {
         var b = ast.Tree.init(child_allocator, source);
         b.source_type = options.source_type;
 
@@ -93,10 +93,14 @@ pub fn parseArrow(parser: *Parser, is_async: bool, arrow_start: u32) Error!?ast.
 
 // rewind on failure so jsx or a `<T>` assertion can win
 pub fn tryParseArrow(parser: *Parser, is_async: bool, arrow_start: u32) Error!?ast.NodeIndex {
+    const head = parser.current_token.span.start;
+    if (parser.ts_rejected_speculations.contains(head)) return null;
+
     const cp = parser.checkpoint();
 
     const arrow = (try parseArrow(parser, is_async, arrow_start)) orelse {
         parser.rewind(cp);
+        try parser.ts_rejected_speculations.putNoClobber(parser.allocator(), head, {});
         return null;
     };
 
 
@@ -503,6 +503,12 @@ fn parseInferType(parser: *Parser) Error!?ast.NodeIndex {
 fn parseInferConstraint(parser: *Parser) Error!ast.NodeIndex {
     if (parser.current_token.tag != .extends) return .null;
 
+    const extends_offset = parser.current_token.span.start;
+    const conditional_allowed = !parser.ts_context.disallow_conditional_types;
+    if (conditional_allowed and parser.ts_rejected_speculations.contains(extends_offset)) {
+        return .null;
+    }
+
     const cp = parser.checkpoint();
     try parser.advance() orelse return .null;
 
@@ -513,12 +519,11 @@ fn parseInferConstraint(parser: *Parser) Error!ast.NodeIndex {
     };
     parser.ts_context.disallow_conditional_types = cp.ts_context.disallow_conditional_types;
 
-    const yields_to_conditional =
-        !cp.ts_context.disallow_conditional_types and
-        parser.current_token.tag == .question;
+    const yields_to_conditional = conditional_allowed and parser.current_token.tag == .question;
 
     if (yields_to_conditional) {
         parser.rewind(cp);
+        try parser.ts_rejected_speculations.putNoClobber(parser.allocator(), extends_offset, {});
         return .null;
     }