Blink parity: glue by-reference arrow fn space; gate to 0.1%

.github/workflows/blink_parity_mautic.yaml

@@ -95,7 +95,7 @@ jobs:
             - name: Compare the two trees
               run: |
                   # ratchet gate: fail once the differing share crosses this; lower it as parity improves
-                  MAX_DIFF_PERCENT=0.15
+                  MAX_DIFF_PERCENT=0.1
                   total=0
                   differ=0
                   differing_files=""

blink/internal/fixer/rules/gen3_func.go

@@ -46,6 +46,23 @@ func fnEnsureSingleSpaceBefore(s *tokens.Stream, i int) bool {
 
 // fnGlueAfter removes a single-line whitespace token immediately after i, gluing
 // the token at i to the following significant token. A newline is left intact.
+// fnIsArrowFn reports whether the "fn" keyword at i opens an arrow function - its
+// parameter "(" follows directly or after a by-reference "&".
+func fnIsArrowFn(s *tokens.Stream, i int) bool {
+	n := nextSignificantIndex(s, i)
+	if n < 0 || s.At(n).Kind != token.Punct {
+		return false
+	}
+	if s.At(n).Value == "(" {
+		return true
+	}
+	if s.At(n).Value == "&" {
+		nn := nextSignificantIndex(s, n)
+		return nn >= 0 && s.At(nn).Kind == token.Punct && s.At(nn).Value == "("
+	}
+	return false
+}
+
 func fnGlueAfter(s *tokens.Stream, i int) bool {
 	if i+1 < s.Len() && s.At(i+1).Kind == token.Whitespace && !hasNewline(s.At(i+1).Value) {
 		s.RemoveAt(i + 1)
@@ -134,9 +151,9 @@ func (f FunctionDeclaration) Fix(s *tokens.Stream) bool {
 				changed = true
 			}
 		case "fn":
-			// arrow function: spacing between "fn" and "(" (closure_fn_spacing)
-			if n := nextSignificantIndex(s, i); n >= 0 &&
-				s.At(n).Kind == token.Punct && s.At(n).Value == "(" {
+			// arrow function: spacing after "fn" (closure_fn_spacing). The "("
+			// follows directly, or after a by-reference "&" ("fn &() => ...").
+			if fnIsArrowFn(s, i) {
 				if f.closureFnSpacingNone {
 					if fnGlueAfter(s, i) {
 						changed = true

blink/internal/fixer/rules/gen3_func_config_test.go

@@ -24,6 +24,18 @@ func TestFunctionDeclarationClosureFnSpacing(t *testing.T) {
 	if want := "<?php $f = fn() => 1;"; !changed || got != want {
 		t.Fatalf("closure_fn_spacing=none: changed=%v got=%q want=%q", changed, got, want)
 	}
+
+	// a by-reference arrow function ("fn &() => ...") also glues the space after fn
+	got, changed = apply(t, cfg, "<?php $f = fn &() => $x;")
+	if want := "<?php $f = fn&() => $x;"; !changed || got != want {
+		t.Fatalf("by-ref fn: changed=%v got=%q want=%q", changed, got, want)
+	}
+
+	// closure_fn_spacing=one keeps a single space for the by-reference form
+	one := FunctionDeclaration{}.WithConfig(map[string]any{"closure_fn_spacing": "one"})
+	if _, changed := apply(t, one, "<?php $f = fn &() => $x;"); changed {
+		t.Fatal("closure_fn_spacing=one must keep the single space in fn &()")
+	}
 }
 
 func TestFunctionDeclarationTrailingCommaSingleLine(t *testing.T) {