SILGen: Allow static stored properties in fully-concrete extensions of generic types.

There's no need for per-instantiation storage in this case, so we can relax the implementation limitation for them.

lib/SILGen/SILGen.cpp

@@ -594,7 +594,8 @@ void SILGenModule::preEmitFunction(SILDeclRef constant,
 
   assert(F->empty() && "already emitted function?!");
 
-  F->setGenericEnvironment(Types.getConstantInfo(constant).GenericEnv);
+  if (F->getLoweredFunctionType()->isPolymorphic())
+    F->setGenericEnvironment(Types.getConstantInfo(constant).GenericEnv);
 
   // Create a debug scope for the function using astNode as source location.
   F->setDebugScope(new (M) SILDebugScope(Loc, F));

lib/SILGen/SILGenGlobalVariable.cpp

@@ -201,8 +201,11 @@ void SILGenModule::emitGlobalInitialization(PatternBindingDecl *pd,
                                             unsigned pbdEntry) {
   // Generic and dynamic static properties require lazy initialization, which
   // isn't implemented yet.
-  if (pd->isStatic())
-    assert(!pd->getDeclContext()->isGenericContext());
+  if (pd->isStatic()) {
+    assert(!pd->getDeclContext()->isGenericContext()
+           || pd->getDeclContext()->getGenericSignatureOfContext()
+                ->areAllParamsConcrete());
+  }
 
   // Emit the lazy initialization token for the initialization expression.
   auto counter = anonymousSymbolCounter++;
@@ -248,7 +251,7 @@ void SILGenModule::emitGlobalInitialization(PatternBindingDecl *pd,
     NewMangling::ASTMangler NewMangler;
     std::string New = NewMangler.mangleGlobalInit(varDecl, counter, true);
     onceFuncBuffer = NewMangling::selectMangling(Old, New);
-}
+  }
 
   SILFunction *onceFunc = emitLazyGlobalInitializer(onceFuncBuffer, pd,
                                                     pbdEntry);

lib/SILGen/SILGenLValue.cpp

@@ -1735,11 +1735,6 @@ void LValue::addMemberVarComponent(SILGenFunction &gen, SILLocation loc,
   // FIXME: This has to be dynamically looked up for classes, and
   // dynamically instantiated for generics.
   if (strategy == AccessStrategy::Storage && var->isStatic()) {
-    auto baseMeta = baseFormalType->castTo<MetatypeType>()->getInstanceType();
-    (void)baseMeta;
-    assert(!baseMeta->is<BoundGenericType>() &&
-           "generic static stored properties not implemented");
-
     // FIXME: this implicitly drops the earlier components, but maybe
     // we ought to evaluate them for side-effects even during the
     // formal access?

lib/SILGen/SILGenType.cpp

@@ -299,10 +299,13 @@ public:
 };
 
 static void emitTypeMemberGlobalVariable(SILGenModule &SGM,
-                                         GenericParamList *generics,
-                                         NominalTypeDecl *theType,
                                          VarDecl *var) {
-  assert(!generics && "generic static properties not implemented");
+  if (var->getDeclContext()->isGenericContext()) {
+    assert(var->getDeclContext()->getGenericSignatureOfContext()
+              ->areAllParamsConcrete()
+           && "generic static vars are not implemented yet");
+  }
+
   if (var->getDeclContext()->getAsClassOrClassExtensionContext()) {
     assert(var->isFinal() && "only 'static' ('class final') stored properties are implemented in classes");
   }
@@ -405,8 +408,7 @@ public:
     // Collect global variables for static properties.
     // FIXME: We can't statically emit a global variable for generic properties.
     if (vd->isStatic() && vd->hasStorage()) {
-      return emitTypeMemberGlobalVariable(SGM, theType->getGenericParams(),
-                                          theType, vd);
+      return emitTypeMemberGlobalVariable(SGM, vd);
     }
 
     visitAbstractStorageDecl(vd);
@@ -494,8 +496,7 @@ public:
       assert(vd->isStatic() && "stored property in extension?!");
       ExtensionDecl *ext = cast<ExtensionDecl>(vd->getDeclContext());
       NominalTypeDecl *theType = ext->getExtendedType()->getAnyNominal();
-      return emitTypeMemberGlobalVariable(SGM, ext->getGenericParams(),
-                                          theType, vd);
+      return emitTypeMemberGlobalVariable(SGM, vd);
     }
     visitAbstractStorageDecl(vd);
   }

lib/Sema/TypeCheckDecl.cpp

@@ -3701,7 +3701,8 @@ public:
 
         // Stored type variables in a generic context need to logically
         // occur once per instantiation, which we don't yet handle.
-        } else if (DC->isGenericContext()) {
+        } else if (DC->isGenericContext()
+               && !DC->getGenericSignatureOfContext()->areAllParamsConcrete()) {
           unimplementedStatic(GenericTypes);
         } else if (DC->getAsClassOrClassExtensionContext()) {
           auto StaticSpelling = PBD->getStaticSpelling();

test/SILGen/static-stored-properties-in-concrete-contexts.swift

@@ -0,0 +1,21 @@
+// RUN: %target-swift-frontend -emit-silgen %s | %FileCheck %s
+
+struct Foo<T> {
+  static var foo: T { return (0 as Int) as! T }
+}
+
+extension Foo where T == Int {
+  // CHECK: sil_global private [[X_TOKEN:@.*]] : $Builtin.Word
+  // CHECK: sil_global hidden [let] @_TZve4mainRxzSirVS_3Foo1xSi : $Int
+  static let x = foo
+
+  // CHECK: sil_global private [[Y_TOKEN:@.*]] : $Builtin.Word
+  // CHECK: sil_global hidden @_TZve4mainRxzSirVS_3Foo1ySi : $Int
+  static var y = foo
+}
+
+print(Foo<Int>.x)
+Foo<Int>.y = 2
+Foo<Int>.y += 3
+print(Foo<Int>.y)
+