Allow referencing static functions in @section expressions

Author: kubamracek

lib/Sema/LegalConstExprVerifier.cpp

@@ -222,10 +222,6 @@ checkSupportedWithSectionAttribute(const Expr *expr,
     if (isa<KeyPathExpr>(expr))
       return std::make_pair(expr, KeyPath);
 
-    // Closure expressions are not supported in constant expressions
-    if (isa<AbstractClosureExpr>(expr))
-      return std::make_pair(expr, Closure);
-
     // Function conversions are allowed if the conversion is to '@convention(c)'
     if (auto functionConvExpr = dyn_cast<FunctionConversionExpr>(expr)) {
       if (auto targetFnTy =
@@ -256,6 +252,60 @@ checkSupportedWithSectionAttribute(const Expr *expr,
       return std::make_pair(expr, OpaqueDeclRef);
     }
 
+    // Allow specific patterns of AutoClosureExpr, which is used in static func
+    // references. E.g. "MyStruct.staticFunc" is:
+    // - autoclosure_expr type="() -> ()"
+    //   - call_expr type="()"
+    //     - dot_syntax_call_expr
+    //       - declref_expr decl="MyStruct.staticFunc"
+    //       - dot_self_expr type="MyStruct.Type"
+    //         - type_expr type="MyStruct.Type"
+    if (auto autoClosureExpr = dyn_cast<AutoClosureExpr>(expr)) {
+      auto subExpr = autoClosureExpr->getUnwrappedCurryThunkExpr();
+      if (auto dotSyntaxCall = dyn_cast<DotSyntaxCallExpr>(subExpr)) {
+        if (auto declRef = dyn_cast<DeclRefExpr>(dotSyntaxCall->getFn())) {
+          if (auto funcDecl = dyn_cast<FuncDecl>(declRef->getDecl())) {
+            // Check if it's a function on a concrete non-generic type
+            if (!funcDecl->hasGenericParamList() &&
+                !funcDecl->getDeclContext()->isGenericContext() &&
+                funcDecl->isStatic()) {
+              if (auto args = dotSyntaxCall->getArgs()) {
+                if (args->size() == 1) {
+                  // Check that the single arg is a DotSelfExpr with only a
+                  // direct concrete TypeExpr inside
+                  if (auto dotSelfExpr =
+                          dyn_cast<DotSelfExpr>(args->get(0).getExpr())) {
+                    if (const TypeExpr *typeExpr =
+                            dyn_cast<TypeExpr>(dotSelfExpr->getSubExpr())) {
+                      auto baseType = typeExpr->getType();
+                      if (baseType && baseType->is<MetatypeType>()) {
+                        auto instanceType =
+                            baseType->getMetatypeInstanceType();
+                        if (auto nominal =
+                                instanceType
+                                    ->getNominalOrBoundGenericNominal()) {
+                          if (!nominal->hasGenericParamList() &&
+                              !nominal->getDeclContext()->isGenericContext() &&
+                              !nominal->isResilient()) {
+                            continue;
+                          }
+                        }
+                      }
+                    }
+                  }
+                }
+              }
+            }
+          }
+        }
+      }
+      return std::make_pair(expr, Default);
+    }
+
+    // Other closure expressions (auto-closures) are not allowed
+    if (isa<AbstractClosureExpr>(expr))
+      return std::make_pair(expr, Default);
+
     // DotSelfExpr for metatype references (but only a direct TypeExpr inside)
     if (const DotSelfExpr *dotSelfExpr = dyn_cast<DotSelfExpr>(expr)) {
       if (const TypeExpr *typeExpr =

test/ConstValues/SectionSyntactic.swift

@@ -43,19 +43,41 @@
 func foo() -> Int { return 42 }
 func bar(x: Int) -> String { return "test" }
 
-// function references
+// global function references
 @section("mysection") let funcRef1 = foo // ok
 @section("mysection") let funcRef2 = bar // ok
 @section("mysection") let funcRef3: ()->Int = foo // ok
 @section("mysection") let funcRef4: @convention(c) ()->Int = foo // ok
 
+struct Q {
+  func memberFunc() {}
+  static func staticFunc() {}
+  func genericFunc<T>(t: T) {}
+  static func staticGenericFunc<T>(t: T) {}
+}
+
+// non-global function references
+@section("mysection") let staticFuncRef1 = Q.staticFunc // ok
+extension Q { @section("mysection") static let staticFuncRef2 = staticFunc } // ok
+@section("mysection") let staticFuncRef3 = Bool.random // ok
+
 // invalid function references (should be rejected)
 @section("mysection") let invalidFuncRef1 = foo()
 // expected-error@-1{{not supported in a constant expression}}
 @section("mysection") let invalidFuncRef2 = Bool.self.random
 // expected-error@-1{{closures not supported in a constant expression}}
 @section("mysection") let invalidFuncRef3 = (Bool.self as Bool.Type).random
 // expected-error@-1{{not supported in a constant expression}}
+@section("mysection") let invalidFuncRef4 = Q.memberFunc
+// expected-error@-1{{not supported in a constant expression}}
+extension Q { @section("mysection") static let invalidFuncRef5 = memberFunc }
+// expected-error@-1{{not supported in a constant expression}}
+extension Q { @section("mysection") static let invalidFuncRef6: (Int)->() = genericFunc(Q()) }
+// expected-error@-1{{not supported in a constant expression}}
+extension Q { @section("mysection") static let invalidFuncRef7: (Q) -> (Int) -> () = genericFunc }
+// expected-error@-1{{not supported in a constant expression}}
+extension Q { @section("mysection") static let invalidFuncRef8: (Int)->() = staticGenericFunc }
+// expected-error@-1{{not supported in a constant expression}}
 
 // generic function references (should be rejected)
 @section("mysection") let invalidGenericFunc = [Int].randomElement