[parser] Support declaring function typed parameters

This adds parser support for using `final` and `var` in function type parameters of primary constructors.

Part of #61699

Change-Id: I32c0b9ac9700fc6a4ccfdd6c732c3ae3179ad5fb
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/457023
Reviewed-by: Konstantin Shcheglov <[email protected]>
Reviewed-by: Brian Wilkerson <[email protected]>
Commit-Queue: Johnni Winther <[email protected]>

Author: johnniwinther

pkg/_fe_analyzer_shared/lib/src/parser/parser_impl.dart

@@ -2209,10 +2209,20 @@ class Parser {
         Token closer = typeParam.skip(token);
         if (closer.next!.isA(TokenType.OPEN_PAREN)) {
           if (varFinalOrConst != null) {
-            reportRecoverableError(
-              varFinalOrConst,
-              codes.codeFunctionTypedParameterVar,
-            );
+            if (memberKind != MemberKind.PrimaryConstructor) {
+              reportRecoverableError(
+                varFinalOrConst,
+                codes.codeFunctionTypedParameterVar,
+              );
+            } else {
+              if (!_isDeclaringConstructorsFeatureEnabled) {
+                reportExperimentNotEnabled(
+                  ExperimentalFlag.declaringConstructors,
+                  varFinalOrConst,
+                  varFinalOrConst,
+                );
+              }
+            }
           }
           beforeInlineFunctionType = token;
           token = closer.next!.endGroup!;
@@ -2221,10 +2231,20 @@ class Parser {
       }
     } else if (next.isA(TokenType.OPEN_PAREN)) {
       if (varFinalOrConst != null) {
-        reportRecoverableError(
-          varFinalOrConst,
-          codes.codeFunctionTypedParameterVar,
-        );
+        if (memberKind != MemberKind.PrimaryConstructor) {
+          reportRecoverableError(
+            varFinalOrConst,
+            codes.codeFunctionTypedParameterVar,
+          );
+        } else {
+          if (!_isDeclaringConstructorsFeatureEnabled) {
+            reportExperimentNotEnabled(
+              ExperimentalFlag.declaringConstructors,
+              varFinalOrConst,
+              varFinalOrConst,
+            );
+          }
+        }
       }
       beforeInlineFunctionType = token;
       token = next.endGroup!;

pkg/front_end/parser_testcases/declaring_constructors/declaring_parameter.dart

@@ -5,6 +5,14 @@ class C(var a) {}
 class C(final a) {}
 class C(var a b) {}
 class C(final a b) {}
+class C(var f()) {}
+class C(final f()) {}
+class C(var void f()) {}
+class C(final void f()) {}
+class C(var f<T>()) {}
+class C(final f<T>()) {}
+class C(var void f<T>()) {}
+class C(final void f<T>()) {}
 
 enum E() {}
 enum E(a) {}
@@ -13,6 +21,14 @@ enum E(var a) {}
 enum E(final a) {}
 enum E(var a b) {}
 enum E(final a b) {}
+enum E(var f()) {}
+enum E(final f()) {}
+enum E(var void f()) {}
+enum E(final void f()) {}
+enum E(var f<T>()) {}
+enum E(final f<T>()) {}
+enum E(var void f<T>()) {}
+enum E(final void f<T>()) {}
 
 extension type ET() {}
 extension type ET(a) {}
@@ -21,3 +37,11 @@ extension type ET(var a) {}
 extension type ET(final a) {}
 extension type ET(var a b) {}
 extension type ET(final a b) {}
+extension type ET(var f()) {}
+extension type ET(final f()) {}
+extension type ET(var void f()) {}
+extension type ET(final void f()) {}
+extension type ET(var f<T>()) {}
+extension type ET(final f<T>()) {}
+extension type ET(var void f<T>()) {}
+extension type ET(final void f<T>()) {}