[Diagnostics] Support @_semantics("swiftui.requires_constant_range")

include/swift/AST/DiagnosticsSema.def

@@ -7862,6 +7862,13 @@ ERROR(atomics_ordering_must_be_constant, none,
       "ordering argument must be a static method or property of %0",
       (Identifier))
 
+//------------------------------------------------------------------------------
+// MARK: SwiftUI
+//------------------------------------------------------------------------------
+
+WARNING(swiftui_arg_must_be_integer_literal, none,
+        "argument must be an integer literal", ())
+
 //------------------------------------------------------------------------------
 // MARK: access notes
 //------------------------------------------------------------------------------

include/swift/AST/SemanticAttrs.def

@@ -96,6 +96,8 @@ SEMANTICS_ATTR(OSLOG_REQUIRES_CONSTANT_ARGUMENTS, "oslog.requires_constant_argum
 SEMANTICS_ATTR(OSLOG_LOG_WITH_LEVEL, "oslog.log_with_level")
 SEMANTICS_ATTR(ATOMICS_REQUIRES_CONSTANT_ORDERINGS, "atomics.requires_constant_orderings")
 
+SEMANTICS_ATTR(SWIFT_UI_REQUIRES_CONSTANT_RANGE, "swiftui.requires_constant_range")
+
 SEMANTICS_ATTR(TYPE_CHECKER_OPEN_EXISTENTIAL, "typechecker._openExistential(_:do:)")
 SEMANTICS_ATTR(TYPE_CHECKER_TYPE, "typechecker.type(of:)")
 SEMANTICS_ATTR(TYPE_CHECKER_WITHOUT_ACTUALLY_ESCAPING, "typechecker.withoutActuallyEscaping(_:do:)")

lib/Sema/ConstantnessSemaDiagnostics.cpp

@@ -76,6 +76,8 @@ static bool isParamRequiredToBeConstant(AbstractFunctionDecl *funcDecl, ParamDec
     nominal = paramType->getNominalOrBoundGenericNominal();
     return !nominal || !isOSLogDynamicObject(nominal);
   }
+  if (hasSemanticsAttr(funcDecl, semantics::SWIFT_UI_REQUIRES_CONSTANT_RANGE))
+    return param->getParameterName().str() == "data";
   if (!hasSemanticsAttr(funcDecl,
                         semantics::ATOMICS_REQUIRES_CONSTANT_ORDERINGS))
     return false;
@@ -245,6 +247,12 @@ static void diagnoseError(Expr *errorExpr, const ASTContext &astContext,
     return;
   }
 
+  if (hasSemanticsAttr(funcDecl,
+        semantics::SWIFT_UI_REQUIRES_CONSTANT_RANGE)) {
+    diags.diagnose(errorLoc, diag::swiftui_arg_must_be_integer_literal);
+    return;
+  }
+
   // Diagnose os_log specific errors here.
 
   // Diagnose primitive stdlib types.

test/Sema/diag_constantness_check_swift_ui.swift

@@ -0,0 +1,34 @@
+// RUN: %target-typecheck-verify-swift
+
+// Replicating the SwiftUI framework `ForEach` from the SDK
+public struct ForEach<Data, ID, Content> where Data : Swift.RandomAccessCollection, ID: Swift.Hashable {
+    public var data: Data
+    public var content: (Data.Element) -> Content
+}
+
+public protocol View {}
+public struct AView: View {}
+
+extension ForEach where Content : View {
+    public init(_ data: Data, id: Swift.KeyPath<Data.Element, ID>, content: @escaping (Data.Element) -> Content) {
+        self.data = data
+        self.content = content
+    }
+}
+
+extension ForEach where Data == Swift.Range<Swift.Int>, ID == Swift.Int, Content : View {
+    @_semantics("swiftui.requires_constant_range") public init(_ data: Swift.Range<Swift.Int>, content: @escaping (Swift.Int) -> Content)
+}
+
+
+func testSwiftUIForEachInvalid() {
+    let notReallyConstant = 10
+    _ = ForEach(0..<notReallyConstant) { _ in AView() }
+    // expected-warning@-1 {{argument must be an integer literal}}
+}
+
+func testSwiftUIForEachValid() {
+    _ = ForEach(0..<10) { _ in AView() }
+    let notReallyConstant = 10
+    _ = ForEach(0..<notReallyConstant, id: \.self) { _ in AView() }
+}