Error on usage of @inline(always) on non-final class methods

Author: aschwaighofer

include/swift/AST/DiagnosticsSema.def

@@ -8934,6 +8934,12 @@ ERROR(attr_inline_always_requires_inlinable,none,
       "together with '@inlinable'", ())
 ERROR(attr_inline_always_no_usable_from_inline,none,
       "cannot use '@inline(always)' together with '@usableFromInline'", ())
+ERROR(attr_inline_always_requires_final_method,none,
+      "'@inline(always)' on class %select{methods|vars}1 requires %0 to be "
+      "marked 'final'", (DeclName, bool))
+ERROR(attr_inline_always_on_accessor,none,
+      "'@inline(always)' on class variable accessors whose variable declaration"
+      " is not final are not allowed", ())
 
 #define UNDEFINE_DIAGNOSTIC_MACROS
 #include "DefineDiagnosticMacros.h"

lib/Sema/TypeCheckAttr.cpp

@@ -3713,6 +3713,37 @@ void AttributeChecker::visitInlineAttr(InlineAttr *attr) {
     diagnoseAndRemoveAttr(attr, diag::attr_inline_always_no_usable_from_inline);
     return;
   }
+  // Check that @inline(always) is only used on statically dispatched methods
+  // (final, static, and methods in extensions mostly).
+  bool isAccessorDecl = false;
+  if (auto *accessorDecl = dyn_cast<AccessorDecl>(D)) {
+    VD = accessorDecl->getStorage();
+    isAccessorDecl = true;
+  }
+
+  auto dc = dyn_cast<ClassDecl>(VD->getDeclContext());
+  if (!dc)
+   return;
+  // In a `class` context.
+
+  if (dc->isActor())
+    return;
+
+  if (auto *vd = dyn_cast<VarDecl>(VD)) {
+    if (vd->isFinal())
+      return;
+    if (isAccessorDecl) {
+      diagnoseAndRemoveAttr(attr, diag::attr_inline_always_on_accessor);
+    } else {
+      diagnoseAndRemoveAttr(attr, diag::attr_inline_always_requires_final_method,
+                            vd->getName(), true/*isVar*/);
+    }
+  } else if (auto *afd = dyn_cast<AbstractFunctionDecl>(VD)) {
+    if (afd->isFinal())
+      return;
+    diagnoseAndRemoveAttr(attr, diag::attr_inline_always_requires_final_method,
+                              afd->getName(), false/*isVar*/);
+  }
 }
 
 void AttributeChecker::visitInlinableAttr(InlinableAttr *attr) {

test/Sema/inline_always.swift

@@ -70,3 +70,63 @@ public var x: Int {
        return 1
    }
 }
+
+class C {
+  static func staticMethodInA() {} // okay
+
+  @inline(always)
+  final func myMethod() {} // okay
+
+  @inline(always) // expected-error {{'@inline(always)' on class methods requires 'myMethod2()' to be marked 'final'}}
+  func myMethod2() {}
+
+  @inline(always)
+  final var myVarFinal : Int { // okay
+    return 0
+  }
+
+  @inline(always) // expected-error {{'@inline(always)' on class vars requires 'myVar' to be marked 'final'}}
+  var myVar : Int {
+    return 0
+  }
+
+  @inline(always)
+  final var myVar2Final: Int { // okay
+    get {
+      return 1
+    }
+  }
+
+  @inline(always) // expected-error {{'@inline(always)' on class vars requires 'myVar2' to be marked 'final'}}
+  var myVar2: Int {
+    get {
+      return 1
+    }
+  }
+
+  final var myVar3Final : Int { // okay
+    @inline(always)
+    get {
+      return 1
+    }
+  }
+
+
+  var myVar3: Int {
+    @inline(always) // expected-error {{'@inline(always)' on class variable accessors whose variable declaration is not final are not allowed}}
+    get {
+      return 1
+    }
+  }
+
+  @inline(always)
+  static func myMethod3() {} // okay
+}
+
+extension C {
+  @inline(always)
+  final func myMethod10() {} // okay
+
+  @inline(always)
+  func myMethod11() {} // okay
+}