[Sema][os_log] Allow wrapping os_log strings within constant evaluable functions

lib/Sema/ConstantnessSemaDiagnostics.cpp

@@ -92,6 +92,13 @@ static bool hasConstantEvaluableAttr(ValueDecl *decl) {
   return hasSemanticsAttr(decl, semantics::CONSTANT_EVALUABLE);
 }
 
+/// Return true iff the \p decl is annotated with oslog.message.init semantics
+/// attribute.
+static bool isOSLogMessageInitializer(ValueDecl *decl) {
+  return hasSemanticsAttr(decl, semantics::OSLOG_MESSAGE_INIT_STRING_LITERAL) ||
+         hasSemanticsAttr(decl, semantics::OSLOG_MESSAGE_INIT_INTERPOLATION);
+}
+
 /// Check whether \p expr is a compile-time constant. It must either be a
 /// literal_expr, which does not include array and dictionary literal, or a
 /// closure expression, which is considered a compile-time constant of a
@@ -162,12 +169,6 @@ static Expr *checkConstantness(Expr *expr) {
     if (!isa<ApplyExpr>(expr))
       return expr;
 
-    if (NominalTypeDecl *nominal =
-        expr->getType()->getNominalOrBoundGenericNominal()) {
-      if (nominal->getName() == nominal->getASTContext().Id_OSLogMessage)
-        return expr;
-    }
-
     ApplyExpr *apply = cast<ApplyExpr>(expr);
     ValueDecl *calledValue = apply->getCalledValue();
     if (!calledValue)
@@ -179,10 +180,18 @@ static Expr *checkConstantness(Expr *expr) {
       continue;
     }
 
+    AbstractFunctionDecl *callee = dyn_cast<AbstractFunctionDecl>(calledValue);
+    if (!callee)
+      return expr;
+
+    // If this is an application of OSLogMessage initializer, fail the check
+    // as this type must be created from string interpolations.
+    if (isOSLogMessageInitializer(callee))
+      return expr;
+
     // If this is a constant_evaluable function, check whether the arguments are
     // constants.
-    AbstractFunctionDecl *callee = dyn_cast<AbstractFunctionDecl>(calledValue);
-    if (!callee || !hasConstantEvaluableAttr(callee))
+    if (!hasConstantEvaluableAttr(callee))
       return expr;
     expressionsToCheck.push_back(apply->getArg());
   }

test/SILOptimizer/OSLogMandatoryOptTest.swift

@@ -635,3 +635,41 @@ extension TestProtocolSelfTypeCapture {
   }
 }
 
+// Test that SwiftUI's preview transformations work with the logging APIs.
+
+// A function similar to the one used by SwiftUI preview to wrap string
+// literals.
+@_semantics("constant_evaluable")
+@_transparent
+public func __designTimeStringStub(
+  _ key: String,
+  fallback: OSLogMessage
+) -> OSLogMessage {
+  fallback
+}
+
+// CHECK-LABEL: @${{.*}}testSwiftUIPreviewWrappingyy
+func testSwiftUIPreviewWrapping() {
+  _osLogTestHelper(__designTimeStringStub("key", fallback: "percent: %"))
+    // CHECK: string_literal utf8 "percent: %%"
+    // CHECK-NOT: OSLogMessage
+    // CHECK-NOT: OSLogInterpolation
+    // CHECK-LABEL: end sil function '${{.*}}testSwiftUIPreviewWrappingyy
+}
+
+
+func functionTakingClosure(_ x: () -> Void) { }
+
+func testWrappingWithinClosures(x: Int) {
+  functionTakingClosure {
+    _osLogTestHelper(
+      __designTimeStringStub(
+        "key",
+        fallback: "escaping of percent: %"))
+      // CHECK-LABEL: @${{.*}}testWrappingWithinClosures1xySi_tFyyXEfU_
+      // CHECK: string_literal utf8 "escaping of percent: %%"
+      // CHECK-NOT: OSLogMessage
+      // CHECK-NOT: OSLogInterpolation
+      // CHECK-LABEL: end sil function '${{.*}}testWrappingWithinClosures1xySi_tFyyXEfU_
+  }
+}

test/Sema/diag_constantness_check_os_log.swift

@@ -155,3 +155,32 @@ func testNonConstantLogObjectLevel(
   osLogWithLevel(level, log: log, message)
     // expected-error@-1 {{argument must be a string interpolation}}
 }
+
+// Test that log messages can be wrapped in constant_evaluable functions.
+
+// A function similar to the one used by SwiftUI preview to wrap string
+// literals.
+@_semantics("constant_evaluable")
+public func __designTimeStringStub(
+  _ key: String,
+  fallback: OSLogMessage
+) -> OSLogMessage {
+  fallback
+}
+
+func testSwiftUIPreviewWrapping() {
+  // This should not produce any diagnostics.
+  _osLogTestHelper(__designTimeStringStub("key", fallback: "A literal message"))
+}
+
+public func nonConstantFunction(
+  _ key: String,
+  fallback: OSLogMessage
+) -> OSLogMessage {
+  fallback
+}
+
+func testLogMessageWrappingDiagnostics() {
+  _osLogTestHelper(nonConstantFunction("key", fallback: "A literal message"))
+    // expected-error@-1{{argument must be a string interpolation}}
+}