diff --git a/pkg/front_end/parser_testcases/error_recovery/bracket_mismatch_00.dart.parser.expect b/pkg/front_end/parser_testcases/error_recovery/bracket_mismatch_00.dart.parser.expect
index fa741ec..a33099b 100644
--- a/pkg/front_end/parser_testcases/error_recovery/bracket_mismatch_00.dart.parser.expect
+++ b/pkg/front_end/parser_testcases/error_recovery/bracket_mismatch_00.dart.parser.expect
@@ -10,7 +10,7 @@
 void bad() {
 [
 (
-])
+*synthetic*])
 ];
 }
 
diff --git a/pkg/front_end/parser_testcases/error_recovery/bracket_mismatch_01.dart.parser.expect b/pkg/front_end/parser_testcases/error_recovery/bracket_mismatch_01.dart.parser.expect
index bbde7fc..88db884 100644
--- a/pkg/front_end/parser_testcases/error_recovery/bracket_mismatch_01.dart.parser.expect
+++ b/pkg/front_end/parser_testcases/error_recovery/bracket_mismatch_01.dart.parser.expect
@@ -26,7 +26,7 @@
 D(),
 D(),
 D(),
-]),
+*synthetic*]),
 D(),
 D(),
 ],
diff --git a/pkg/front_end/parser_testcases/error_recovery/bracket_mismatch_03.dart.parser.expect b/pkg/front_end/parser_testcases/error_recovery/bracket_mismatch_03.dart.parser.expect
index b435d9f..e7f22b1 100644
--- a/pkg/front_end/parser_testcases/error_recovery/bracket_mismatch_03.dart.parser.expect
+++ b/pkg/front_end/parser_testcases/error_recovery/bracket_mismatch_03.dart.parser.expect
@@ -1,7 +1,7 @@
 NOTICE: Stream was rewritten by parser!
 
 void foo() {
-{foo();;);}
+{foo();*synthetic*;);}
 }
 
 void[KeywordToken] foo[StringToken]([BeginToken])[SimpleToken] {[BeginToken]
diff --git a/pkg/front_end/parser_testcases/error_recovery/bracket_mismatch_04.dart.parser.expect b/pkg/front_end/parser_testcases/error_recovery/bracket_mismatch_04.dart.parser.expect
index 5106907..efe56f1 100644
--- a/pkg/front_end/parser_testcases/error_recovery/bracket_mismatch_04.dart.parser.expect
+++ b/pkg/front_end/parser_testcases/error_recovery/bracket_mismatch_04.dart.parser.expect
@@ -1,7 +1,7 @@
 NOTICE: Stream was rewritten by parser!
 
 void foo() {
-foo(() {bar();;);});
+foo(() {bar();*synthetic*;);});
 }
 
 
diff --git a/pkg/front_end/parser_testcases/error_recovery/bracket_mismatch_06.dart.parser.expect b/pkg/front_end/parser_testcases/error_recovery/bracket_mismatch_06.dart.parser.expect
index 7750cc4..470b5c5 100644
--- a/pkg/front_end/parser_testcases/error_recovery/bracket_mismatch_06.dart.parser.expect
+++ b/pkg/front_end/parser_testcases/error_recovery/bracket_mismatch_06.dart.parser.expect
@@ -1,7 +1,7 @@
 NOTICE: Stream was rewritten by parser!
 
 main() {
-new C();
+new C(*synthetic*);
 }
 
 
diff --git a/pkg/front_end/parser_testcases/error_recovery/empty_await_for.dart.parser.expect b/pkg/front_end/parser_testcases/error_recovery/empty_await_for.dart.parser.expect
index 981f0c9..71785e5 100644
--- a/pkg/front_end/parser_testcases/error_recovery/empty_await_for.dart.parser.expect
+++ b/pkg/front_end/parser_testcases/error_recovery/empty_await_for.dart.parser.expect
@@ -1,7 +1,7 @@
 NOTICE: Stream was rewritten by parser!
 
 main() async {
-await for (in) {}
+await for (*synthetic*in*synthetic*) {}
 }
 
 
diff --git a/pkg/front_end/parser_testcases/error_recovery/empty_for.dart.parser.expect b/pkg/front_end/parser_testcases/error_recovery/empty_for.dart.parser.expect
index 792bb5b..0e27283 100644
--- a/pkg/front_end/parser_testcases/error_recovery/empty_for.dart.parser.expect
+++ b/pkg/front_end/parser_testcases/error_recovery/empty_for.dart.parser.expect
@@ -1,7 +1,7 @@
 NOTICE: Stream was rewritten by parser!
 
 main() {
-for (;;) {}
+for (*synthetic*;*synthetic*;) {}
 }
 
 
diff --git a/pkg/front_end/parser_testcases/error_recovery/issue_39024.crash_dart.parser.expect b/pkg/front_end/parser_testcases/error_recovery/issue_39024.crash_dart.parser.expect
index 91d29ba..df28256 100644
--- a/pkg/front_end/parser_testcases/error_recovery/issue_39024.crash_dart.parser.expect
+++ b/pkg/front_end/parser_testcases/error_recovery/issue_39024.crash_dart.parser.expect
@@ -1,5 +1,5 @@
 NOTICE: Stream was rewritten by parser!
 
-n<S e()>(){}
+n<S e()>*synthetic*(){}
 
 [UnmatchedToken][UnmatchedToken]n[StringToken]<[BeginToken]S[StringToken] e[StringToken]([BeginToken])[SyntheticToken]>[SyntheticToken][SyntheticStringToken]([SyntheticBeginToken])[SyntheticToken]{[SyntheticBeginToken]}[SyntheticToken][SimpleToken]
diff --git a/pkg/front_end/parser_testcases/error_recovery/issue_39033.crash_dart.parser.expect b/pkg/front_end/parser_testcases/error_recovery/issue_39033.crash_dart.parser.expect
index 72d15cd..69c448d 100644
--- a/pkg/front_end/parser_testcases/error_recovery/issue_39033.crash_dart.parser.expect
+++ b/pkg/front_end/parser_testcases/error_recovery/issue_39033.crash_dart.parser.expect
@@ -1,5 +1,5 @@
 NOTICE: Stream was rewritten by parser!
 
-typedef F<Glib>.=;
+typedef F<Glib>.=*synthetic*;
 
 typedef[KeywordToken] F[StringToken]<[BeginToken]Glib[StringToken]>[SyntheticToken].[SimpleToken]=[SimpleToken][SyntheticStringToken];[SyntheticToken][SimpleToken]
diff --git a/pkg/front_end/parser_testcases/error_recovery/issue_39058.crash_dart.parser.expect b/pkg/front_end/parser_testcases/error_recovery/issue_39058.crash_dart.parser.expect
index 9d79365..ac60159 100644
--- a/pkg/front_end/parser_testcases/error_recovery/issue_39058.crash_dart.parser.expect
+++ b/pkg/front_end/parser_testcases/error_recovery/issue_39058.crash_dart.parser.expect
@@ -1,5 +1,5 @@
 NOTICE: Stream was rewritten by parser!
 
-{<[]()>[];}
+{<*synthetic*[]()>[];}
 
 [UnmatchedToken][UnmatchedToken][UnmatchedToken]{[BeginToken]<[BeginToken][SyntheticStringToken][][SimpleToken]([BeginToken])[SyntheticToken]>[SyntheticToken][[SyntheticBeginToken]][SyntheticToken];[SyntheticToken]}[SyntheticToken][SimpleToken]
diff --git a/pkg/front_end/parser_testcases/error_recovery/issue_39058_prime.crash_dart.parser.expect b/pkg/front_end/parser_testcases/error_recovery/issue_39058_prime.crash_dart.parser.expect
index 211d516..fd52b9b5 100644
--- a/pkg/front_end/parser_testcases/error_recovery/issue_39058_prime.crash_dart.parser.expect
+++ b/pkg/front_end/parser_testcases/error_recovery/issue_39058_prime.crash_dart.parser.expect
@@ -1,6 +1,6 @@
 NOTICE: Stream was rewritten by parser!
 
-{<[]()>[];}
+{<*synthetic*[]()>[];}
 
 
 {[BeginToken]<[BeginToken][SyntheticStringToken][][SimpleToken]([BeginToken])[SimpleToken]>[SimpleToken][[SyntheticBeginToken]][SyntheticToken];[SyntheticToken]}[SimpleToken]
diff --git a/pkg/front_end/parser_testcases/error_recovery/issue_39060.dart.parser.expect b/pkg/front_end/parser_testcases/error_recovery/issue_39060.dart.parser.expect
index 2e5f3d3..35b2b5e 100644
--- a/pkg/front_end/parser_testcases/error_recovery/issue_39060.dart.parser.expect
+++ b/pkg/front_end/parser_testcases/error_recovery/issue_39060.dart.parser.expect
@@ -1,7 +1,7 @@
 NOTICE: Stream was rewritten by parser!
 
 main() {
-{s A;<}>
+{s A;<*synthetic*}>
 [];}
 
 main[StringToken]([BeginToken])[SimpleToken] {[BeginToken]
diff --git a/pkg/front_end/parser_testcases/error_recovery/issue_39202.crash_dart.parser.expect b/pkg/front_end/parser_testcases/error_recovery/issue_39202.crash_dart.parser.expect
index 7ea04bc..c55bc84 100644
--- a/pkg/front_end/parser_testcases/error_recovery/issue_39202.crash_dart.parser.expect
+++ b/pkg/front_end/parser_testcases/error_recovery/issue_39202.crash_dart.parser.expect
@@ -1,5 +1,5 @@
 NOTICE: Stream was rewritten by parser!
 
-() async ()=> a ;b < c $? >;
+() async ()=> a ;b < c $? >*synthetic*;
 
 ([BeginToken])[SimpleToken] async[KeywordToken] ([SyntheticBeginToken])[SyntheticToken]=>[SimpleToken] a[StringToken] ;[SyntheticToken]b[StringToken] <[BeginToken] c[StringToken] $[StringToken]?[SimpleToken] >[SimpleToken][SyntheticStringToken];[SyntheticToken][SimpleToken]
diff --git a/pkg/front_end/parser_testcases/error_recovery/issue_42229.crash_dart.parser.expect b/pkg/front_end/parser_testcases/error_recovery/issue_42229.crash_dart.parser.expect
index 8f68d8f..17af764 100644
--- a/pkg/front_end/parser_testcases/error_recovery/issue_42229.crash_dart.parser.expect
+++ b/pkg/front_end/parser_testcases/error_recovery/issue_42229.crash_dart.parser.expect
@@ -1,5 +1,5 @@
 NOTICE: Stream was rewritten by parser!
 
-Stream<List<>> ;
+Stream<List<*synthetic*>> *synthetic*;
 
 Stream[StringToken]<[BeginToken]List[StringToken]<[BeginToken][SyntheticStringToken]>[SimpleToken]>[SimpleToken] [SyntheticStringToken];[SyntheticToken][SimpleToken]
diff --git a/pkg/front_end/parser_testcases/error_recovery/issue_42229_prime.crash_dart.parser.expect b/pkg/front_end/parser_testcases/error_recovery/issue_42229_prime.crash_dart.parser.expect
index 61baa3f..764be00 100644
--- a/pkg/front_end/parser_testcases/error_recovery/issue_42229_prime.crash_dart.parser.expect
+++ b/pkg/front_end/parser_testcases/error_recovery/issue_42229_prime.crash_dart.parser.expect
@@ -1,5 +1,5 @@
 NOTICE: Stream was rewritten by parser!
 
-Stream<List<> >;
+Stream<List<*synthetic*> >*synthetic*;
 
 Stream[StringToken]<[BeginToken]List[StringToken]<[BeginToken][SyntheticStringToken]>[SimpleToken] >[SimpleToken][SyntheticStringToken];[SyntheticToken][SimpleToken]
diff --git a/pkg/front_end/parser_testcases/error_recovery/issue_42229_prime_2.crash_dart.parser.expect b/pkg/front_end/parser_testcases/error_recovery/issue_42229_prime_2.crash_dart.parser.expect
index 33d84d2..67936e5 100644
--- a/pkg/front_end/parser_testcases/error_recovery/issue_42229_prime_2.crash_dart.parser.expect
+++ b/pkg/front_end/parser_testcases/error_recovery/issue_42229_prime_2.crash_dart.parser.expect
@@ -1,5 +1,5 @@
 NOTICE: Stream was rewritten by parser!
 
-Stream<List<>> foo() {}
+Stream<List<*synthetic*>> foo() {}
 
 Stream[StringToken]<[BeginToken]List[StringToken]<[BeginToken][SyntheticStringToken]>[SimpleToken]>[SimpleToken] foo[StringToken]([BeginToken])[SimpleToken] {[BeginToken]}[SimpleToken][SimpleToken]
diff --git a/pkg/front_end/parser_testcases/error_recovery/issue_42229_prime_3.crash_dart.parser.expect b/pkg/front_end/parser_testcases/error_recovery/issue_42229_prime_3.crash_dart.parser.expect
index a3a072f..41c9b4a 100644
--- a/pkg/front_end/parser_testcases/error_recovery/issue_42229_prime_3.crash_dart.parser.expect
+++ b/pkg/front_end/parser_testcases/error_recovery/issue_42229_prime_3.crash_dart.parser.expect
@@ -1,5 +1,5 @@
 NOTICE: Stream was rewritten by parser!
 
-Stream<List<x>> ;
+Stream<List<x>> *synthetic*;
 
 Stream[StringToken]<[BeginToken]List[StringToken]<[BeginToken]x[StringToken]>[SimpleToken]>[SimpleToken] [SyntheticStringToken];[SyntheticToken][SimpleToken]
diff --git a/pkg/front_end/parser_testcases/error_recovery/issue_42267.dart.parser.expect b/pkg/front_end/parser_testcases/error_recovery/issue_42267.dart.parser.expect
index ab5a595..78d1eaf 100644
--- a/pkg/front_end/parser_testcases/error_recovery/issue_42267.dart.parser.expect
+++ b/pkg/front_end/parser_testcases/error_recovery/issue_42267.dart.parser.expect
@@ -3,10 +3,10 @@
 void main() {
 builder..foo[bar];
 FilterSet((builder) => builder..foo[bar]);
-builder..foo[];
-FilterSet((builder) => builder..foo[]);
-builder..foo[ ];
-FilterSet((builder) => builder..foo[ ]);
+builder..foo[*synthetic*];
+FilterSet((builder) => builder..foo[*synthetic*]);
+builder..foo[ *synthetic*];
+FilterSet((builder) => builder..foo[ *synthetic*]);
 }
 
 void[KeywordToken] main[StringToken]([BeginToken])[SimpleToken] {[BeginToken]
diff --git a/pkg/front_end/parser_testcases/error_recovery/issue_43090.crash_dart.parser.expect b/pkg/front_end/parser_testcases/error_recovery/issue_43090.crash_dart.parser.expect
index 2ee22c4..315d42c 100644
--- a/pkg/front_end/parser_testcases/error_recovery/issue_43090.crash_dart.parser.expect
+++ b/pkg/front_end/parser_testcases/error_recovery/issue_43090.crash_dart.parser.expect
@@ -1,6 +1,6 @@
 NOTICE: Stream was rewritten by parser!
 
-typedef A< >= void Function();
+typedef A< *synthetic*>= void Function();
 
 
 typedef[KeywordToken] A[StringToken]<[BeginToken] [SyntheticStringToken]>[SyntheticToken]=[SimpleToken] void[KeywordToken] Function[KeywordToken]([BeginToken])[SimpleToken];[SimpleToken]
diff --git a/pkg/front_end/parser_testcases/error_recovery/issue_43090_prime_02.crash_dart.parser.expect b/pkg/front_end/parser_testcases/error_recovery/issue_43090_prime_02.crash_dart.parser.expect
index d4a3d9c..621186b 100644
--- a/pkg/front_end/parser_testcases/error_recovery/issue_43090_prime_02.crash_dart.parser.expect
+++ b/pkg/front_end/parser_testcases/error_recovery/issue_43090_prime_02.crash_dart.parser.expect
@@ -1,6 +1,6 @@
 NOTICE: Stream was rewritten by parser!
 
-typedef A<>= void Function();
+typedef A<*synthetic*>= void Function();
 
 
 typedef[KeywordToken] A[StringToken]<[BeginToken][SyntheticStringToken]>[SimpleToken]=[SimpleToken] void[KeywordToken] Function[KeywordToken]([BeginToken])[SimpleToken];[SimpleToken]
diff --git a/pkg/front_end/parser_testcases/error_recovery/issue_46346_prime_2.dart.parser.expect b/pkg/front_end/parser_testcases/error_recovery/issue_46346_prime_2.dart.parser.expect
index 6294f83..aca66ef 100644
--- a/pkg/front_end/parser_testcases/error_recovery/issue_46346_prime_2.dart.parser.expect
+++ b/pkg/front_end/parser_testcases/error_recovery/issue_46346_prime_2.dart.parser.expect
@@ -1,5 +1,5 @@
 NOTICE: Stream was rewritten by parser!
 
-class{}
+class*synthetic*{}
 
 class[KeywordToken][SyntheticStringToken]{[SyntheticBeginToken]}[SyntheticToken][SimpleToken]
diff --git a/pkg/front_end/parser_testcases/error_recovery/issue_46505.crash_dart.parser.expect b/pkg/front_end/parser_testcases/error_recovery/issue_46505.crash_dart.parser.expect
index 5329c0d..3630ae3 100644
--- a/pkg/front_end/parser_testcases/error_recovery/issue_46505.crash_dart.parser.expect
+++ b/pkg/front_end/parser_testcases/error_recovery/issue_46505.crash_dart.parser.expect
@@ -1,7 +1,7 @@
 NOTICE: Stream was rewritten by parser!
 
 class A {
-Stream<List<>>
+Stream<List<*synthetic*>>
 (){}}
 
 class[KeywordToken] A[StringToken] {[BeginToken]
diff --git a/pkg/front_end/parser_testcases/error_recovery/issue_46505_prime_1.crash_dart.parser.expect b/pkg/front_end/parser_testcases/error_recovery/issue_46505_prime_1.crash_dart.parser.expect
index cfe5c55..048f723 100644
--- a/pkg/front_end/parser_testcases/error_recovery/issue_46505_prime_1.crash_dart.parser.expect
+++ b/pkg/front_end/parser_testcases/error_recovery/issue_46505_prime_1.crash_dart.parser.expect
@@ -1,7 +1,7 @@
 NOTICE: Stream was rewritten by parser!
 
 class A {
-Stream<List<>> x() {}
+Stream<List<*synthetic*>> x() {}
 }
 
 class[KeywordToken] A[StringToken] {[BeginToken]
diff --git a/pkg/front_end/parser_testcases/error_recovery/issue_46505_prime_3.crash_dart.parser.expect b/pkg/front_end/parser_testcases/error_recovery/issue_46505_prime_3.crash_dart.parser.expect
index b3d50a3..d529abb 100644
--- a/pkg/front_end/parser_testcases/error_recovery/issue_46505_prime_3.crash_dart.parser.expect
+++ b/pkg/front_end/parser_testcases/error_recovery/issue_46505_prime_3.crash_dart.parser.expect
@@ -1,7 +1,7 @@
 NOTICE: Stream was rewritten by parser!
 
 class A {
-Stream<List<Set<>>>
+Stream<List<Set<*synthetic*>>>
 (){}}
 
 class[KeywordToken] A[StringToken] {[BeginToken]
diff --git a/pkg/front_end/parser_testcases/error_recovery/issue_46505_prime_4.crash_dart.parser.expect b/pkg/front_end/parser_testcases/error_recovery/issue_46505_prime_4.crash_dart.parser.expect
index a2b4071..e4f75a9 100644
--- a/pkg/front_end/parser_testcases/error_recovery/issue_46505_prime_4.crash_dart.parser.expect
+++ b/pkg/front_end/parser_testcases/error_recovery/issue_46505_prime_4.crash_dart.parser.expect
@@ -1,7 +1,7 @@
 NOTICE: Stream was rewritten by parser!
 
 class A {
-Stream<List<Set<List<>>>>
+Stream<List<Set<List<*synthetic*>>>>
 (){}}
 
 class[KeywordToken] A[StringToken] {[BeginToken]
diff --git a/pkg/front_end/parser_testcases/error_recovery/keyword_named_class_methods.dart.parser.expect b/pkg/front_end/parser_testcases/error_recovery/keyword_named_class_methods.dart.parser.expect
index 12d12c3..70d958e 100644
--- a/pkg/front_end/parser_testcases/error_recovery/keyword_named_class_methods.dart.parser.expect
+++ b/pkg/front_end/parser_testcases/error_recovery/keyword_named_class_methods.dart.parser.expect
@@ -28,7 +28,7 @@
 
 int break(int x) {
 if (x == 0) return 42;
-return ;break;(x-1) + 1;
+return *synthetic*;break;(x-1) + 1;
 }
 
 int case(int x) {
@@ -48,12 +48,12 @@
 
 int const(int x) {
 if (x == 0) return 42;
-return const(x-1) + 1;
+return const*synthetic*(x-1) + 1;
 }
 
 int continue(int x) {
 if (x == 0) return 42;
-return ;continue;(x-1) + 1;
+return *synthetic*;continue;(x-1) + 1;
 }
 
 int covariant(int x) {
@@ -73,8 +73,8 @@
 
 int do(int x) {
 if (x == 0) return 42;
-return ;do(x-1) + 1;
-while();}
+return *synthetic*;do(x-1) + 1;
+while(*synthetic*);}
 
 int dynamic(int x) {
 if (x == 0) return 42;
@@ -83,7 +83,7 @@
 
 int else(int x) {
 if (x == 0) return 42;
-return ;;else(x-1) + 1;
+return *synthetic*;*synthetic*;else(x-1) + 1;
 }
 
 int enum(int x) {
@@ -123,7 +123,7 @@
 
 int final(int x) {
 if (x == 0) return 42;
-return ;final(;x-1;;) + 1;
+return *synthetic*;final(*synthetic*;x-1;*synthetic*;) *synthetic*+ 1;
 }
 
 int finally(int x) {
@@ -133,7 +133,7 @@
 
 int for(int x) {
 if (x == 0) return 42;
-return ;for(x-1;;) + 1;
+return *synthetic*;for(x-1;*synthetic*;) *synthetic*+ 1;
 }
 
 int Function(int x) {
@@ -153,7 +153,7 @@
 
 int if(int x) {
 if (x == 0) return 42;
-return ;if(x-1) + 1;
+return *synthetic*;if(x-1) *synthetic*+ 1;
 }
 
 int implements(int x) {
@@ -183,7 +183,7 @@
 
 int is(int x) {
 if (x == 0) return 42;
-return is;(x-1) + 1;
+return *synthetic*is*synthetic*;(x-1) + 1;
 }
 
 int late(int x) {
@@ -208,7 +208,7 @@
 
 int new(int x) {
 if (x == 0) return 42;
-return new(x-1) + 1;
+return new*synthetic*(x-1) + 1;
 }
 
 int null(int x) {
@@ -288,7 +288,7 @@
 
 int switch(int x) {
 if (x == 0) return 42;
-return ;switch(x-1) {}+ 1;
+return *synthetic*;switch(x-1) {}*synthetic*+ 1;
 }
 
 int sync(int x) {
@@ -296,7 +296,7 @@
 return sync(x-1) + 1;
 }
 
-int this;(int x) {
+int this;*synthetic*(int x) {
 if (x == 0) return 42;
 return this(x-1) + 1;
 }
@@ -313,7 +313,7 @@
 
 int try(int x) {
 if (x == 0) return 42;
-return ;try{}(x-1) + 1;
+return *synthetic*;try{}(x-1) + 1;
 }
 
 int typedef(int x) {
@@ -323,17 +323,17 @@
 
 int var(int x) {
 if (x == 0) return 42;
-return ;var(;x-1;;) + 1;
+return *synthetic*;var(*synthetic*;x-1;*synthetic*;) *synthetic*+ 1;
 }
 
 int void(int x) {
 if (x == 0) return 42;
-return ;void(;x-1;;) + 1;
+return *synthetic*;void(*synthetic*;x-1;*synthetic*;) *synthetic*+ 1;
 }
 
 int while(int x) {
 if (x == 0) return 42;
-return ;while(x-1) + 1;
+return *synthetic*;while(x-1) *synthetic*+ 1;
 }
 
 int with(int x) {
diff --git a/pkg/front_end/parser_testcases/error_recovery/keyword_named_top_level_methods.dart.parser.expect b/pkg/front_end/parser_testcases/error_recovery/keyword_named_top_level_methods.dart.parser.expect
index 7620786..65501be 100644
--- a/pkg/front_end/parser_testcases/error_recovery/keyword_named_top_level_methods.dart.parser.expect
+++ b/pkg/front_end/parser_testcases/error_recovery/keyword_named_top_level_methods.dart.parser.expect
@@ -27,7 +27,7 @@
 
 int break(int x) {
 if (x == 0) return 42;
-return ;break;(x-1) + 1;
+return *synthetic*;break;(x-1) + 1;
 }
 
 int case(int x) {
@@ -47,12 +47,12 @@
 
 int const(int x) {
 if (x == 0) return 42;
-return const(x-1) + 1;
+return const*synthetic*(x-1) + 1;
 }
 
 int continue(int x) {
 if (x == 0) return 42;
-return ;continue;(x-1) + 1;
+return *synthetic*;continue;(x-1) + 1;
 }
 
 int covariant(int x) {
@@ -72,8 +72,8 @@
 
 int do(int x) {
 if (x == 0) return 42;
-return ;do(x-1) + 1;
-while();}
+return *synthetic*;do(x-1) + 1;
+while(*synthetic*);}
 
 int dynamic(int x) {
 if (x == 0) return 42;
@@ -82,7 +82,7 @@
 
 int else(int x) {
 if (x == 0) return 42;
-return ;;else(x-1) + 1;
+return *synthetic*;*synthetic*;else(x-1) + 1;
 }
 
 int enum(int x) {
@@ -122,7 +122,7 @@
 
 int final(int x) {
 if (x == 0) return 42;
-return ;final(;x-1;;) + 1;
+return *synthetic*;final(*synthetic*;x-1;*synthetic*;) *synthetic*+ 1;
 }
 
 int finally(int x) {
@@ -132,7 +132,7 @@
 
 int for(int x) {
 if (x == 0) return 42;
-return ;for(x-1;;) + 1;
+return *synthetic*;for(x-1;*synthetic*;) *synthetic*+ 1;
 }
 
 int Function(int x) {
@@ -152,7 +152,7 @@
 
 int if(int x) {
 if (x == 0) return 42;
-return ;if(x-1) + 1;
+return *synthetic*;if(x-1) *synthetic*+ 1;
 }
 
 int implements(int x) {
@@ -182,7 +182,7 @@
 
 int is(int x) {
 if (x == 0) return 42;
-return is;(x-1) + 1;
+return *synthetic*is*synthetic*;(x-1) + 1;
 }
 
 int late(int x) {
@@ -207,7 +207,7 @@
 
 int new(int x) {
 if (x == 0) return 42;
-return new(x-1) + 1;
+return new*synthetic*(x-1) + 1;
 }
 
 int null(int x) {
@@ -287,7 +287,7 @@
 
 int switch(int x) {
 if (x == 0) return 42;
-return ;switch(x-1) {}+ 1;
+return *synthetic*;switch(x-1) {}*synthetic*+ 1;
 }
 
 int sync(int x) {
@@ -312,7 +312,7 @@
 
 int try(int x) {
 if (x == 0) return 42;
-return ;try{}(x-1) + 1;
+return *synthetic*;try{}(x-1) + 1;
 }
 
 int typedef(int x) {
@@ -322,17 +322,17 @@
 
 int var(int x) {
 if (x == 0) return 42;
-return ;var(;x-1;;) + 1;
+return *synthetic*;var(*synthetic*;x-1;*synthetic*;) *synthetic*+ 1;
 }
 
 int void(int x) {
 if (x == 0) return 42;
-return ;void(;x-1;;) + 1;
+return *synthetic*;void(*synthetic*;x-1;*synthetic*;) *synthetic*+ 1;
 }
 
 int while(int x) {
 if (x == 0) return 42;
-return ;while(x-1) + 1;
+return *synthetic*;while(x-1) *synthetic*+ 1;
 }
 
 int with(int x) {
diff --git a/pkg/front_end/parser_testcases/error_recovery/keyword_named_typedefs.dart.parser.expect b/pkg/front_end/parser_testcases/error_recovery/keyword_named_typedefs.dart.parser.expect
index 2727ab4..211f3f3 100644
--- a/pkg/front_end/parser_testcases/error_recovery/keyword_named_typedefs.dart.parser.expect
+++ b/pkg/front_end/parser_testcases/error_recovery/keyword_named_typedefs.dart.parser.expect
@@ -131,7 +131,7 @@
 typedef void var();
 typedef var = void Function();
 typedef void void();
-typedef void ();= void Function();
+typedef void *synthetic*();= void Function();
 typedef void while();
 typedef while = void Function();
 typedef void with();
diff --git a/pkg/front_end/parser_testcases/general/issue_45848_04.dart.parser.expect b/pkg/front_end/parser_testcases/general/issue_45848_04.dart.parser.expect
index 7ffb0fe..994575f 100644
--- a/pkg/front_end/parser_testcases/general/issue_45848_04.dart.parser.expect
+++ b/pkg/front_end/parser_testcases/general/issue_45848_04.dart.parser.expect
@@ -3,7 +3,7 @@
 void f<T>() {}
 
 void m() {
-f<>();
+f<*synthetic*>();
 }
 
 void[KeywordToken] f[StringToken]<[BeginToken]T[StringToken]>[SimpleToken]([BeginToken])[SimpleToken] {[BeginToken]}[SimpleToken]
diff --git a/pkg/front_end/parser_testcases/general/new_as_identifier.dart.parser.expect b/pkg/front_end/parser_testcases/general/new_as_identifier.dart.parser.expect
index f91e9be..9dae5dc 100644
--- a/pkg/front_end/parser_testcases/general/new_as_identifier.dart.parser.expect
+++ b/pkg/front_end/parser_testcases/general/new_as_identifier.dart.parser.expect
@@ -5,7 +5,7 @@
 
 
 
-C.constructor_field_initializer() : =this.{}new operator= (){}null;
+C.constructor_field_initializer() : *synthetic*=this.*synthetic*{}new operator= (){}null;
 }
 
 class D {
diff --git a/pkg/front_end/parser_testcases/nnbd/issue_40267_method_call_no_type_arguments.dart.parser.expect b/pkg/front_end/parser_testcases/nnbd/issue_40267_method_call_no_type_arguments.dart.parser.expect
index 028eb60..b3bac90 100644
--- a/pkg/front_end/parser_testcases/nnbd/issue_40267_method_call_no_type_arguments.dart.parser.expect
+++ b/pkg/front_end/parser_testcases/nnbd/issue_40267_method_call_no_type_arguments.dart.parser.expect
@@ -4,7 +4,7 @@
 var a, b;
 
 a?.call(b);
-a?(b):;
+a?(b):*synthetic*;
 }
 
 f[StringToken]([BeginToken])[SimpleToken] {[BeginToken]
diff --git a/pkg/front_end/parser_testcases/nnbd/issue_40267_method_call_with_type_arguments.dart.parser.expect b/pkg/front_end/parser_testcases/nnbd/issue_40267_method_call_with_type_arguments.dart.parser.expect
index 69c6d67..ed478bb 100644
--- a/pkg/front_end/parser_testcases/nnbd/issue_40267_method_call_with_type_arguments.dart.parser.expect
+++ b/pkg/front_end/parser_testcases/nnbd/issue_40267_method_call_with_type_arguments.dart.parser.expect
@@ -5,7 +5,7 @@
 
 a?.call<Foo>(b);
 a?<Foo>(b);
-:;}
+:*synthetic*;}
 
 f[StringToken]([BeginToken])[SimpleToken] {[BeginToken]
 var[KeywordToken] a[StringToken],[SimpleToken] b[StringToken];[SimpleToken]
diff --git a/pkg/front_end/parser_testcases/nnbd/issue_44477.dart.parser.expect b/pkg/front_end/parser_testcases/nnbd/issue_44477.dart.parser.expect
index 63970d7..bf0db66 100644
--- a/pkg/front_end/parser_testcases/nnbd/issue_44477.dart.parser.expect
+++ b/pkg/front_end/parser_testcases/nnbd/issue_44477.dart.parser.expect
@@ -1,5 +1,5 @@
 NOTICE: Stream was rewritten by parser!
 
-Future<List<>>;
+Future<List<*synthetic*>>*synthetic*;
 
 Future[StringToken]<[BeginToken]List[StringToken]<[BeginToken][SyntheticStringToken]>[SimpleToken]>[SimpleToken][SyntheticStringToken];[SyntheticToken][SimpleToken]
diff --git a/pkg/front_end/test/parser_suite.dart b/pkg/front_end/test/parser_suite.dart
index 86e3f94..f415263 100644
--- a/pkg/front_end/test/parser_suite.dart
+++ b/pkg/front_end/test/parser_suite.dart
@@ -23,6 +23,9 @@
 import 'package:_fe_analyzer_shared/src/scanner/scanner.dart'
     show ErrorToken, ScannerConfiguration, Token, Utf8BytesScanner;
 
+import 'package:_fe_analyzer_shared/src/scanner/token.dart'
+    show SyntheticStringToken;
+
 import 'package:front_end/src/fasta/source/stack_listener_impl.dart'
     show offsetForToken;
 
@@ -365,6 +368,9 @@
       }
       if (token is! ErrorToken) {
         sb.write(token.lexeme);
+        if (!addTypes && token.lexeme == "" && token is SyntheticStringToken) {
+          sb.write("*synthetic*");
+        }
       }
       if (addTypes) {
         sb.write("[${token.runtimeType}]");