[clang] [Parser][ObjC] Add -Wobjc-prefix-length warning option. (PR #97597)

Alastair Houghton via cfe-commits cfe-commits at lists.llvm.org
Thu Jul 4 03:27:54 PDT 2024


https://github.com/al45tair updated https://github.com/llvm/llvm-project/pull/97597

>From 02f7c5ef71b382866e02037ce82c85fa6fcbb394 Mon Sep 17 00:00:00 2001
From: Alastair Houghton <ahoughton at apple.com>
Date: Wed, 3 Jul 2024 17:00:51 +0100
Subject: [PATCH 1/2] [Parser][ObjC] Add -Wobjc-prefix-length warning option.

This lets clang generate warnings automatically if it sees Objective-C
names that don't have the correct prefix length.

rdar://131055157
---
 clang/include/clang/Basic/DiagnosticGroups.td |  1 +
 .../clang/Basic/DiagnosticParseKinds.td       |  7 ++
 clang/include/clang/Basic/LangOptions.def     |  2 +
 clang/include/clang/Driver/Options.td         |  7 ++
 clang/include/clang/Parse/Parser.h            |  1 +
 clang/lib/Driver/ToolChains/Clang.cpp         |  1 +
 clang/lib/Parse/ParseObjc.cpp                 | 65 +++++++++++++++++++
 clang/test/Parser/objc-prefixes.m             | 62 ++++++++++++++++++
 8 files changed, 146 insertions(+)
 create mode 100644 clang/test/Parser/objc-prefixes.m

diff --git a/clang/include/clang/Basic/DiagnosticGroups.td b/clang/include/clang/Basic/DiagnosticGroups.td
index 9431eea1f6be2..0d944434cda38 100644
--- a/clang/include/clang/Basic/DiagnosticGroups.td
+++ b/clang/include/clang/Basic/DiagnosticGroups.td
@@ -598,6 +598,7 @@ def ObjCPointerIntrospect : DiagGroup<"deprecated-objc-pointer-introspection", [
 def ObjCMultipleMethodNames : DiagGroup<"objc-multiple-method-names">;
 def ObjCFlexibleArray : DiagGroup<"objc-flexible-array">;
 def ObjCBoxing : DiagGroup<"objc-boxing">;
+def ObjCPrefixLength : DiagGroup<"objc-prefix-length">;
 def CompletionHandler : DiagGroup<"completion-handler">;
 def CalledOnceParameter : DiagGroup<"called-once-parameter", [CompletionHandler]>;
 def OpenCLUnsupportedRGBA: DiagGroup<"opencl-unsupported-rgba">;
diff --git a/clang/include/clang/Basic/DiagnosticParseKinds.td b/clang/include/clang/Basic/DiagnosticParseKinds.td
index 12aab09f28556..7e26bd13f9c7b 100644
--- a/clang/include/clang/Basic/DiagnosticParseKinds.td
+++ b/clang/include/clang/Basic/DiagnosticParseKinds.td
@@ -563,6 +563,13 @@ def err_declaration_does_not_declare_param : Error<
   "declaration does not declare a parameter">;
 def err_no_matching_param : Error<"parameter named %0 is missing">;
 
+def warn_objc_unprefixed_class_name : Warning<
+  "un-prefixed Objective-C class name">,
+  InGroup<ObjCPrefixLength>;
+def warn_objc_unprefixed_protocol_name : Warning<
+  "un-prefixed Objective-C protocol name">,
+  InGroup<ObjCPrefixLength>;
+
 /// Objective-C++ parser diagnostics
 def err_expected_token_instead_of_objcxx_keyword : Error<
   "expected %0; %1 is a keyword in Objective-C++">;
diff --git a/clang/include/clang/Basic/LangOptions.def b/clang/include/clang/Basic/LangOptions.def
index 491759e2fcdbb..9df19b01f0b22 100644
--- a/clang/include/clang/Basic/LangOptions.def
+++ b/clang/include/clang/Basic/LangOptions.def
@@ -351,6 +351,8 @@ LANGOPT(ObjCAutoRefCount , 1, 0, "Objective-C automated reference counting")
 LANGOPT(ObjCWeakRuntime     , 1, 0, "__weak support in the ARC runtime")
 LANGOPT(ObjCWeak            , 1, 0, "Objective-C __weak in ARC and MRC files")
 LANGOPT(ObjCSubscriptingLegacyRuntime         , 1, 0, "Subscripting support in legacy ObjectiveC runtime")
+BENIGN_LANGOPT(ObjCPrefixLength, 32, 0,
+               "if non-zero, warn about Objective-C classes or protocols with names that do not have a prefix of the specified length.")
 BENIGN_LANGOPT(CompatibilityQualifiedIdBlockParamTypeChecking, 1, 0,
                "compatibility mode for type checking block parameters "
                "involving qualified id types")
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index 1ede75d3782cd..829efafd03a2c 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -3418,6 +3418,13 @@ defm objc_exceptions : BoolFOption<"objc-exceptions",
   PosFlag<SetTrue, [], [ClangOption, CC1Option],
           "Enable Objective-C exceptions">,
   NegFlag<SetFalse>>;
+def Wobjc_prefix_length_EQ:
+  Joined<["-"], "Wobjc-prefix-length=">,
+  Visibility<[ClangOption, CC1Option]>,
+  MetaVarName<"<N>">,
+  HelpText<"Warn if Objective-C class or protocol names do not start with a prefix of the specified length">,
+  MarshallingInfoInt<LangOpts<"ObjCPrefixLength">>;
+
 defm application_extension : BoolFOption<"application-extension",
   LangOpts<"AppExt">, DefaultFalse,
   PosFlag<SetTrue, [], [ClangOption, CC1Option],
diff --git a/clang/include/clang/Parse/Parser.h b/clang/include/clang/Parse/Parser.h
index 6880fa4bb0b03..0e2fdc44321b5 100644
--- a/clang/include/clang/Parse/Parser.h
+++ b/clang/include/clang/Parse/Parser.h
@@ -1704,6 +1704,7 @@ class Parser : public CodeCompletionHandler {
 
   // Objective-C External Declarations
   void MaybeSkipAttributes(tok::ObjCKeywordKind Kind);
+  bool isValidObjCPublicName(StringRef name);
   DeclGroupPtrTy ParseObjCAtDirectives(ParsedAttributes &DeclAttrs,
                                        ParsedAttributes &DeclSpecAttrs);
   DeclGroupPtrTy ParseObjCAtClassDeclaration(SourceLocation atLoc);
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index 27c451c565f2b..c66914b0686c8 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -6291,6 +6291,7 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
   }
 
   Args.AddAllArgs(CmdArgs, options::OPT_Wsystem_headers_in_module_EQ);
+  Args.AddLastArg(CmdArgs, options::OPT_Wobjc_prefix_length_EQ);
 
   if (Args.hasFlag(options::OPT_pedantic, options::OPT_no_pedantic, false))
     CmdArgs.push_back("-pedantic");
diff --git a/clang/lib/Parse/ParseObjc.cpp b/clang/lib/Parse/ParseObjc.cpp
index 6a2088a73c55b..006328140d0eb 100644
--- a/clang/lib/Parse/ParseObjc.cpp
+++ b/clang/lib/Parse/ParseObjc.cpp
@@ -204,6 +204,57 @@ void Parser::CheckNestedObjCContexts(SourceLocation AtLoc)
     Diag(Decl->getBeginLoc(), diag::note_objc_container_start) << (int)ock;
 }
 
+/// An Objective-C public name (a class name or protocol name) is
+/// expected to have a prefix as all names are in a single global
+/// namespace.
+///
+/// If the -Wobjc-prefix-length is set to N, the name must start
+/// with N+1 capital letters, which must be followed by a character
+/// that is not a capital letter.
+///
+/// For instance, for N set to 2, the following are valid:
+///
+///          NSString
+///          NSArray
+///
+///      but these are not:
+///
+///          MyString
+///          NSKString
+///          NSnotAString
+///
+/// We make a special exception for NSCF things when the prefix is set
+/// to length 2, because that's an unusual special case in the implementation
+/// of the Cocoa frameworks.
+///
+/// Names that start with underscores are exempt from this check, but
+/// are reserved for the system and should not be used by user code.
+bool Parser::isValidObjCPublicName(StringRef name) {
+  size_t nameLen = name.size();
+  size_t requiredUpperCase = getLangOpts().ObjCPrefixLength + 1;
+
+  if (name.starts_with('_'))
+    return true;
+
+  // Special case for NSCF when prefix length is 2
+  if (requiredUpperCase == 3 && nameLen > 4 && name.starts_with("NSCF") &&
+      isUppercase(name[4]) && (nameLen == 5 || !isUppercase(name[5])))
+    return true;
+
+  if (nameLen < requiredUpperCase)
+    return false;
+
+  for (size_t n = 0; n < requiredUpperCase; ++n) {
+    if (!isUppercase(name[n]))
+      return false;
+  }
+
+  if (nameLen > requiredUpperCase && isUppercase(name[requiredUpperCase]))
+    return false;
+
+  return true;
+}
+
 ///
 ///   objc-interface:
 ///     objc-class-interface-attributes[opt] objc-class-interface
@@ -319,6 +370,14 @@ Decl *Parser::ParseObjCAtInterfaceDeclaration(SourceLocation AtLoc,
 
     return CategoryType;
   }
+
+  // Not a category - we are declaring a class
+  if (getLangOpts().ObjCPrefixLength &&
+      !PP.getSourceManager().isInSystemHeader(nameLoc) &&
+      !isValidObjCPublicName(nameId->getName())) {
+    Diag(nameLoc, diag::warn_objc_unprefixed_class_name);
+  }
+
   // Parse a class interface.
   IdentifierInfo *superClassId = nullptr;
   SourceLocation superClassLoc;
@@ -2081,6 +2140,12 @@ Parser::ParseObjCAtProtocolDeclaration(SourceLocation AtLoc,
   IdentifierInfo *protocolName = Tok.getIdentifierInfo();
   SourceLocation nameLoc = ConsumeToken();
 
+  if (getLangOpts().ObjCPrefixLength &&
+      !PP.getSourceManager().isInSystemHeader(nameLoc) &&
+      !isValidObjCPublicName(protocolName->getName())) {
+    Diag(nameLoc, diag::warn_objc_unprefixed_protocol_name);
+  }
+
   if (TryConsumeToken(tok::semi)) { // forward declaration of one protocol.
     IdentifierLocPair ProtoInfo(protocolName, nameLoc);
     return Actions.ObjC().ActOnForwardProtocolDeclaration(AtLoc, ProtoInfo,
diff --git a/clang/test/Parser/objc-prefixes.m b/clang/test/Parser/objc-prefixes.m
new file mode 100644
index 0000000000000..32c8448f93fbe
--- /dev/null
+++ b/clang/test/Parser/objc-prefixes.m
@@ -0,0 +1,62 @@
+// RUN: %clang_cc1 %s -Wobjc-prefix-length=2 -fsyntax-only -verify
+
+// Test prefix length rules for ObjC interfaces and protocols
+
+// -- Plain interfaces --------------------------------------------------------
+
+ at interface _Foo
+ at end
+
+ at interface Foo // expected-warning {{un-prefixed Objective-C class name}}
+ at end
+
+ at interface NSFoo
+ at end
+
+// Special case for prefix-length 2
+ at interface NSCFFoo
+ at end
+
+ at interface NSCFXFoo // expected-warning {{un-prefixed Objective-C class name}}
+ at end
+
+ at interface NSXFoo // expected-warning {{un-prefixed Objective-C class name}}
+ at end
+
+// -- Categories --------------------------------------------------------------
+
+// Categories don't trigger these warnings
+
+ at interface Foo (Bar)
+ at end
+
+ at interface NSFoo (Bar)
+ at end
+
+ at interface NSCFFoo (Bar)
+ at end
+
+ at interface NSXFoo (Bar)
+ at end
+
+// -- Protocols ---------------------------------------------------------------
+
+ at protocol _FooProtocol
+ at end
+
+ at protocol FooProtocol // expected-warning {{un-prefixed Objective-C protocol name}}
+ at end
+
+ at protocol NSFooProtocol
+ at end
+
+// Special case for prefix-length 2
+ at protocol NSCFFooProtocol
+ at end
+
+ at protocol NSCFXFooProtocol // expected-warning {{un-prefixed Objective-C protocol name}}
+ at end
+
+ at protocol NSXFooProtocol // expected-warning {{un-prefixed Objective-C protocol name}}
+ at end
+

>From a0331bb896bc3d0a58b5bd4bdb81b7c31f0a3446 Mon Sep 17 00:00:00 2001
From: Alastair Houghton <ahoughton at apple.com>
Date: Wed, 3 Jul 2024 18:14:34 +0100
Subject: [PATCH 2/2] [Parser][ObjC] Add -Wobjc-prefix warning option.

This allows you to specify a comma separated list of allowed prefixes,
as an alternative to the -Wobjc-prefix-length option.

rdar://131055157
---
 clang/include/clang/Basic/DiagnosticGroups.td |  1 +
 .../clang/Basic/DiagnosticParseKinds.td       |  7 +++
 clang/include/clang/Basic/LangOptions.def     |  2 +-
 clang/include/clang/Basic/LangOptions.h       |  3 ++
 clang/include/clang/Driver/Options.td         | 10 +++-
 clang/include/clang/Parse/Parser.h            |  1 +
 clang/lib/Driver/ToolChains/Clang.cpp         |  2 +
 clang/lib/Parse/ParseObjc.cpp                 | 50 ++++++++++++++++---
 clang/test/Parser/objc-prefixes2.m            | 27 ++++++++++
 9 files changed, 92 insertions(+), 11 deletions(-)
 create mode 100644 clang/test/Parser/objc-prefixes2.m

diff --git a/clang/include/clang/Basic/DiagnosticGroups.td b/clang/include/clang/Basic/DiagnosticGroups.td
index 0d944434cda38..d78a042955e94 100644
--- a/clang/include/clang/Basic/DiagnosticGroups.td
+++ b/clang/include/clang/Basic/DiagnosticGroups.td
@@ -598,6 +598,7 @@ def ObjCPointerIntrospect : DiagGroup<"deprecated-objc-pointer-introspection", [
 def ObjCMultipleMethodNames : DiagGroup<"objc-multiple-method-names">;
 def ObjCFlexibleArray : DiagGroup<"objc-flexible-array">;
 def ObjCBoxing : DiagGroup<"objc-boxing">;
+def ObjCPrefix : DiagGroup<"objc-prefix">;
 def ObjCPrefixLength : DiagGroup<"objc-prefix-length">;
 def CompletionHandler : DiagGroup<"completion-handler">;
 def CalledOnceParameter : DiagGroup<"called-once-parameter", [CompletionHandler]>;
diff --git a/clang/include/clang/Basic/DiagnosticParseKinds.td b/clang/include/clang/Basic/DiagnosticParseKinds.td
index 7e26bd13f9c7b..ae82bdbff7870 100644
--- a/clang/include/clang/Basic/DiagnosticParseKinds.td
+++ b/clang/include/clang/Basic/DiagnosticParseKinds.td
@@ -570,6 +570,13 @@ def warn_objc_unprefixed_protocol_name : Warning<
   "un-prefixed Objective-C protocol name">,
   InGroup<ObjCPrefixLength>;
 
+def warn_objc_bad_class_name_prefix : Warning<
+  "Objective-C class name prefix not in permitted list">,
+  InGroup<ObjCPrefix>;
+def warn_objc_bad_protocol_name_prefix : Warning<
+  "Objective-C protocol name prefix not in permitted list">,
+  InGroup<ObjCPrefix>;
+
 /// Objective-C++ parser diagnostics
 def err_expected_token_instead_of_objcxx_keyword : Error<
   "expected %0; %1 is a keyword in Objective-C++">;
diff --git a/clang/include/clang/Basic/LangOptions.def b/clang/include/clang/Basic/LangOptions.def
index 9df19b01f0b22..ea5752363f58c 100644
--- a/clang/include/clang/Basic/LangOptions.def
+++ b/clang/include/clang/Basic/LangOptions.def
@@ -351,7 +351,7 @@ LANGOPT(ObjCAutoRefCount , 1, 0, "Objective-C automated reference counting")
 LANGOPT(ObjCWeakRuntime     , 1, 0, "__weak support in the ARC runtime")
 LANGOPT(ObjCWeak            , 1, 0, "Objective-C __weak in ARC and MRC files")
 LANGOPT(ObjCSubscriptingLegacyRuntime         , 1, 0, "Subscripting support in legacy ObjectiveC runtime")
-BENIGN_LANGOPT(ObjCPrefixLength, 32, 0,
+BENIGN_VALUE_LANGOPT(ObjCPrefixLength, 32, 0,
                "if non-zero, warn about Objective-C classes or protocols with names that do not have a prefix of the specified length.")
 BENIGN_LANGOPT(CompatibilityQualifiedIdBlockParamTypeChecking, 1, 0,
                "compatibility mode for type checking block parameters "
diff --git a/clang/include/clang/Basic/LangOptions.h b/clang/include/clang/Basic/LangOptions.h
index 91f1c2f2e6239..2a525228597bb 100644
--- a/clang/include/clang/Basic/LangOptions.h
+++ b/clang/include/clang/Basic/LangOptions.h
@@ -499,6 +499,9 @@ class LangOptions : public LangOptionsBase {
 
   std::string ObjCConstantStringClass;
 
+  /// Allowed prefixes for ObjC classes and protocols
+  std::vector<std::string> ObjCAllowedPrefixes;
+
   /// The name of the handler function to be called when -ftrapv is
   /// specified.
   ///
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index 829efafd03a2c..7a7e21c59501b 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -3418,11 +3418,17 @@ defm objc_exceptions : BoolFOption<"objc-exceptions",
   PosFlag<SetTrue, [], [ClangOption, CC1Option],
           "Enable Objective-C exceptions">,
   NegFlag<SetFalse>>;
+def Wobjc_prefix_EQ:
+  CommaJoined<["-"], "Wobjc-prefix=">, Group<W_value_Group>,
+  Visibility<[ClangOption, CC1Option]>,
+  MetaVarName<"<prefixes>">,
+  HelpText<"Warn if Objective-C class or protocol names do not start with any prefix in a comma separated list <prefixes>.  Takes precedence over -Wobjc-prefix-length">,
+  MarshallingInfoStringVector<LangOpts<"ObjCAllowedPrefixes">>;
 def Wobjc_prefix_length_EQ:
-  Joined<["-"], "Wobjc-prefix-length=">,
+  Joined<["-"], "Wobjc-prefix-length=">, Group<W_value_Group>,
   Visibility<[ClangOption, CC1Option]>,
   MetaVarName<"<N>">,
-  HelpText<"Warn if Objective-C class or protocol names do not start with a prefix of the specified length">,
+  HelpText<"Warn if Objective-C class or protocol names do not start with a prefix of the specified length. -Wobjc-prefix takes precedence if set">,
   MarshallingInfoInt<LangOpts<"ObjCPrefixLength">>;
 
 defm application_extension : BoolFOption<"application-extension",
diff --git a/clang/include/clang/Parse/Parser.h b/clang/include/clang/Parse/Parser.h
index 0e2fdc44321b5..61f7dad5680e7 100644
--- a/clang/include/clang/Parse/Parser.h
+++ b/clang/include/clang/Parse/Parser.h
@@ -1704,6 +1704,7 @@ class Parser : public CodeCompletionHandler {
 
   // Objective-C External Declarations
   void MaybeSkipAttributes(tok::ObjCKeywordKind Kind);
+  bool isObjCPublicNamePrefixAllowed(StringRef name);
   bool isValidObjCPublicName(StringRef name);
   DeclGroupPtrTy ParseObjCAtDirectives(ParsedAttributes &DeclAttrs,
                                        ParsedAttributes &DeclSpecAttrs);
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index c66914b0686c8..0163c641de78c 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -6291,6 +6291,8 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
   }
 
   Args.AddAllArgs(CmdArgs, options::OPT_Wsystem_headers_in_module_EQ);
+
+  Args.AddAllArgs(CmdArgs, options::OPT_Wobjc_prefix_EQ);
   Args.AddLastArg(CmdArgs, options::OPT_Wobjc_prefix_length_EQ);
 
   if (Args.hasFlag(options::OPT_pedantic, options::OPT_no_pedantic, false))
diff --git a/clang/lib/Parse/ParseObjc.cpp b/clang/lib/Parse/ParseObjc.cpp
index 006328140d0eb..226b058add0ad 100644
--- a/clang/lib/Parse/ParseObjc.cpp
+++ b/clang/lib/Parse/ParseObjc.cpp
@@ -208,6 +208,13 @@ void Parser::CheckNestedObjCContexts(SourceLocation AtLoc)
 /// expected to have a prefix as all names are in a single global
 /// namespace.
 ///
+/// If the `-Wobjc-prefix=<list>` option is active, it specifies a list
+/// of permitted prefixes; classes and protocols must start with a
+/// prefix from that list.  Note that in this case, we check that
+/// the name matches <prefix>(<upper-case><not-upper-case>?)?, so e.g.
+/// if you specify `-Wobjc-prefix=NS`, then `NSURL` would not be valid;
+/// you would want to specify `-Wobjc-prefix=NS,NSURL` in that case.
+///
 /// If the -Wobjc-prefix-length is set to N, the name must start
 /// with N+1 capital letters, which must be followed by a character
 /// that is not a capital letter.
@@ -229,10 +236,35 @@ void Parser::CheckNestedObjCContexts(SourceLocation AtLoc)
 ///
 /// Names that start with underscores are exempt from this check, but
 /// are reserved for the system and should not be used by user code.
+bool Parser::isObjCPublicNamePrefixAllowed(StringRef name) {
+  size_t nameLen = name.size();
+
+  // If there's nothing in the list, it's allowed
+  if (getLangOpts().ObjCAllowedPrefixes.empty())
+    return true;
+
+  // Otherwise it must start with a list entry, optionally followed by
+  // an uppercase letter and then optionally by something that isn't an
+  // uppercase letter.
+  for (StringRef prefix : getLangOpts().ObjCAllowedPrefixes) {
+    size_t prefixLen = prefix.size();
+    if (nameLen >= prefixLen && name.starts_with(prefix) &&
+        (nameLen == prefixLen || isUppercase(name[prefixLen])) &&
+        (nameLen == prefixLen + 1 || !isUppercase(name[prefixLen + 1])))
+      return true;
+  }
+
+  return false;
+}
+
 bool Parser::isValidObjCPublicName(StringRef name) {
   size_t nameLen = name.size();
   size_t requiredUpperCase = getLangOpts().ObjCPrefixLength + 1;
 
+  // If ObjCPrefixLength is zero, we do no further checking
+  if (requiredUpperCase == 1)
+    return true;
+
   if (name.starts_with('_'))
     return true;
 
@@ -372,10 +404,11 @@ Decl *Parser::ParseObjCAtInterfaceDeclaration(SourceLocation AtLoc,
   }
 
   // Not a category - we are declaring a class
-  if (getLangOpts().ObjCPrefixLength &&
-      !PP.getSourceManager().isInSystemHeader(nameLoc) &&
-      !isValidObjCPublicName(nameId->getName())) {
-    Diag(nameLoc, diag::warn_objc_unprefixed_class_name);
+  if (!PP.getSourceManager().isInSystemHeader(nameLoc)) {
+    if (!isObjCPublicNamePrefixAllowed(nameId->getName()))
+      Diag(nameLoc, diag::warn_objc_bad_class_name_prefix);
+    else if (!isValidObjCPublicName(nameId->getName()))
+      Diag(nameLoc, diag::warn_objc_unprefixed_class_name);
   }
 
   // Parse a class interface.
@@ -2140,10 +2173,11 @@ Parser::ParseObjCAtProtocolDeclaration(SourceLocation AtLoc,
   IdentifierInfo *protocolName = Tok.getIdentifierInfo();
   SourceLocation nameLoc = ConsumeToken();
 
-  if (getLangOpts().ObjCPrefixLength &&
-      !PP.getSourceManager().isInSystemHeader(nameLoc) &&
-      !isValidObjCPublicName(protocolName->getName())) {
-    Diag(nameLoc, diag::warn_objc_unprefixed_protocol_name);
+  if (!PP.getSourceManager().isInSystemHeader(nameLoc)) {
+    if (!isObjCPublicNamePrefixAllowed(protocolName->getName()))
+      Diag(nameLoc, diag::warn_objc_bad_protocol_name_prefix);
+    else if (!isValidObjCPublicName(protocolName->getName()))
+      Diag(nameLoc, diag::warn_objc_unprefixed_protocol_name);
   }
 
   if (TryConsumeToken(tok::semi)) { // forward declaration of one protocol.
diff --git a/clang/test/Parser/objc-prefixes2.m b/clang/test/Parser/objc-prefixes2.m
new file mode 100644
index 0000000000000..2d9ba88f65d43
--- /dev/null
+++ b/clang/test/Parser/objc-prefixes2.m
@@ -0,0 +1,27 @@
+// RUN: %clang_cc1 %s -Wobjc-prefixes=NS,NSCF,NSURL -fsyntax-only -verify
+
+// Test prefix list rules
+
+ at interface Foo // expected-warning {{Objective-C class name prefix not in permitted list}}
+ at end
+
+ at interface NSFoo
+ at end
+
+ at interface NSfoo // expected-warning {{Objective-C class name prefix not in permitted list}}
+ at end
+
+ at interface NSFFoo // expected-warning {{Objective-C class name prefix not in permitted list}}
+ at end
+
+ at interface NSCFFoo
+ at end
+
+ at interface NSURL
+ at end
+
+ at interface NSURLFoo
+ at end
+
+ at interface NSRGBColor // expected-warning {{Objective-C class name prefix not in permitted list}}
+ at end



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