Add feature for value generic namelookup

Author: Azoy

include/swift/Basic/Features.def

@@ -256,6 +256,7 @@ LANGUAGE_FEATURE(RawIdentifiers, 451, "Raw identifiers")
 LANGUAGE_FEATURE(SendableCompletionHandlers, 463, "Objective-C completion handler parameters are imported as @Sendable")
 LANGUAGE_FEATURE(AsyncExecutionBehaviorAttributes, 0, "@concurrent and nonisolated(nonsending)")
 LANGUAGE_FEATURE(IsolatedConformances, 407, "Global-actor isolated conformances")
+LANGUAGE_FEATURE(ValueGenericsNameLookup, 452, "Value generics appearing as static members for namelookup")
 
 // Swift 6
 UPCOMING_FEATURE(ConciseMagicFile, 274, 6)

lib/AST/FeatureSet.cpp

@@ -12,6 +12,7 @@
 
 #include "FeatureSet.h"
 
+#include "swift/AST/ASTWalker.h"
 #include "swift/AST/Decl.h"
 #include "swift/AST/ExistentialLayout.h"
 #include "swift/AST/GenericParamList.h"
@@ -470,6 +471,54 @@ static bool usesFeatureValueGenerics(Decl *decl) {
   return false;
 }
 
+class UsesTypeValueExpr : public ASTWalker {
+public:
+  bool used = false;
+
+  PreWalkResult<Expr *> walkToExprPre(Expr *expr) override {
+    if (isa<TypeValueExpr>(expr)) {
+      used = true;
+      return Action::Stop();
+    }
+
+    return Action::Continue(expr);
+  }
+};
+
+static bool usesFeatureValueGenericsNameLookup(Decl *decl) {
+  // Be conservative and mark any function that has a TypeValueExpr in its body
+  // as having used this feature. It's a little difficult to fine grain this
+  // check because the following:
+  //
+  // func a() -> Int {
+  //   A<123>.n
+  // }
+  //
+  // Would appear to have the same expression as something like:
+  //
+  // extension A where n == 123 {
+  //   func b() -> Int {
+  //     n
+  //   }
+  // }
+
+  auto fn = dyn_cast<AbstractFunctionDecl>(decl);
+
+  if (!fn)
+    return false;
+
+  auto body = fn->getTypecheckedBody();
+
+  if (!body)
+    return false;
+
+  UsesTypeValueExpr utve;
+
+  body->walk(utve);
+
+  return utve.used;
+}
+
 static bool usesFeatureCoroutineAccessors(Decl *decl) {
   auto accessorDeclUsesFeatureCoroutineAccessors = [](AccessorDecl *accessor) {
     return requiresFeatureCoroutineAccessors(accessor->getAccessorKind());

test/ModuleInterface/value_generics.swift

@@ -14,6 +14,8 @@ public struct Slab<Element, let N: Int> {
   public var count: Int {
     N
   }
+
+  public init() {}
 }
 
 // CHECK: public func usesGenericSlab<let N : Swift.Int>(_: ValueGeneric.Slab<Swift.Int, N>)
@@ -24,3 +26,27 @@ public func usesConcreteSlab(_: Slab<Int, 2>) {}
 
 // CHECK: public func usesNegativeSlab(_: ValueGeneric.Slab<Swift.String, -10>)
 public func usesNegativeSlab(_: Slab<String, -10>) {}
+
+// CHECK: $ValueGenericsNameLookup
+@inlinable
+public func test() -> Int {
+  // CHECK: Slab<Int, 123>.N
+  Slab<Int, 123>.N
+}
+
+// CHECK: $ValueGenericsNameLookup
+@inlinable
+public func test2() -> Int {
+  // CHECK: type(of: Slab<Int, 123>()).N
+  type(of: Slab<Int, 123>()).N
+}
+
+// CHECK: $ValueGenericsNameLookup
+@inlinable
+public func test3() {
+  {
+    print(123)
+    print(123)
+    print(Slab<Int, 123>.N)
+  }()
+}

test/Sema/value_generics.swift

@@ -131,6 +131,14 @@ struct E<A, let b: Int> { // expected-note {{'b' previously declared here}}
 
   func b() {} // expected-error {{invalid redeclaration of 'b()'}}
               // expected-note@-1 {{'b' declared here}}
+
+  func dumb() -> Int {
+    Self.b // OK
+  }
+
+  static func dumb2() -> Int {
+    Self.b // OK
+  }
 }
 
 func testE1() -> Int {