[clang] Extend diagnose_if to accept more detailed warning information, take 2 (#119712)

This is take two of #70976. This iteration of the patch makes sure that
custom
diagnostics without any warning group don't get promoted by `-Werror` or
`-Wfatal-errors`.

This implements parts of the extension proposed in
https://discourse.llvm.org/t/exposing-the-diagnostic-engine-to-c/73092/7.

Specifically, this makes it possible to specify a diagnostic group in an
optional third argument.

13 files changed, 256 insertions, 153 deletions

diff --git a/clang/lib/Basic/Diagnostic.cpp b/clang/lib/Basic/Diagnostic.cpp
index ae71758..9e2f134 100644
--- a/clang/lib/Basic/Diagnostic.cpp
+++ b/clang/lib/Basic/Diagnostic.cpp
@@ -145,7 +145,7 @@ void DiagnosticsEngine::Reset(bool soft /*=false*/) {
 
     // Create a DiagState and DiagStatePoint representing diagnostic changes
     // through command-line.
-    DiagStates.emplace_back();
+    DiagStates.emplace_back(*Diags);
     DiagStatesByLoc.appendFirst(&DiagStates.back());
   }
 }
@@ -156,8 +156,11 @@ DiagnosticsEngine::DiagState::getOrAddMapping(diag::kind Diag) {
       DiagMap.insert(std::make_pair(Diag, DiagnosticMapping()));
 
   // Initialize the entry if we added it.
-  if (Result.second)
-    Result.first->second = DiagnosticIDs::getDefaultMapping(Diag);
+  if (Result.second) {
+    Result.first->second = DiagIDs.getDefaultMapping(Diag);
+    if (DiagnosticIDs::IsCustomDiag(Diag))
+      DiagIDs.initCustomDiagMapping(Result.first->second, Diag);
+  }
 
   return Result.first->second;
 }
@@ -299,7 +302,8 @@ void DiagnosticsEngine::DiagStateMap::dump(SourceManager &SrcMgr,
 
       for (auto &Mapping : *Transition.State) {
         StringRef Option =
-            DiagnosticIDs::getWarningOptionForDiag(Mapping.first);
+            SrcMgr.getDiagnostics().Diags->getWarningOptionForDiag(
+                Mapping.first);
         if (!DiagName.empty() && DiagName != Option)
           continue;
 
@@ -343,9 +347,7 @@ void DiagnosticsEngine::PushDiagStatePoint(DiagState *State,
 
 void DiagnosticsEngine::setSeverity(diag::kind Diag, diag::Severity Map,
                                     SourceLocation L) {
-  assert(Diag < diag::DIAG_UPPER_LIMIT &&
-         "Can only map builtin diagnostics");
-  assert((Diags->isBuiltinWarningOrExtension(Diag) ||
+  assert((Diags->isWarningOrExtension(Diag) ||
           (Map == diag::Severity::Fatal || Map == diag::Severity::Error)) &&
          "Cannot map errors into warnings!");
   assert((L.isInvalid() || SourceMgr) && "No SourceMgr for valid location");
@@ -397,6 +399,8 @@ bool DiagnosticsEngine::setSeverityForGroup(diag::Flavor Flavor,
   if (Diags->getDiagnosticsInGroup(Flavor, Group, GroupDiags))
     return true;
 
+  Diags->setGroupSeverity(Group, Map);
+
   // Set the mapping.
   for (diag::kind Diag : GroupDiags)
     setSeverity(Diag, Map, Loc);
@@ -419,6 +423,7 @@ bool DiagnosticsEngine::setDiagnosticGroupWarningAsError(StringRef Group,
   if (Enabled)
     return setSeverityForGroup(diag::Flavor::WarningOrError, Group,
                                diag::Severity::Error);
+  Diags->setGroupSeverity(Group, diag::Severity::Warning);
 
   // Otherwise, we want to set the diagnostic mapping's "no Werror" bit, and
   // potentially downgrade anything already mapped to be a warning.
@@ -450,6 +455,7 @@ bool DiagnosticsEngine::setDiagnosticGroupErrorAsFatal(StringRef Group,
   if (Enabled)
     return setSeverityForGroup(diag::Flavor::WarningOrError, Group,
                                diag::Severity::Fatal);
+  Diags->setGroupSeverity(Group, diag::Severity::Error);
 
   // Otherwise, we want to set the diagnostic mapping's "no Wfatal-errors" bit,
   // and potentially downgrade anything already mapped to be a fatal error.
@@ -482,7 +488,7 @@ void DiagnosticsEngine::setSeverityForAll(diag::Flavor Flavor,
 
   // Set the mapping.
   for (diag::kind Diag : AllDiags)
-    if (Diags->isBuiltinWarningOrExtension(Diag))
+    if (Diags->isWarningOrExtension(Diag))
       setSeverity(Diag, Map, Loc);
 }
 
diff --git a/clang/lib/Basic/DiagnosticIDs.cpp b/clang/lib/Basic/DiagnosticIDs.cpp
index de1de6f..ca5b8d2 100644
--- a/clang/lib/Basic/DiagnosticIDs.cpp
+++ b/clang/lib/Basic/DiagnosticIDs.cpp
@@ -62,13 +62,12 @@ const uint32_t StaticDiagInfoDescriptionOffsets[] = {
 #undef DIAG
 };
 
-// Diagnostic classes.
 enum DiagnosticClass {
-  CLASS_NOTE       = 0x01,
-  CLASS_REMARK     = 0x02,
-  CLASS_WARNING    = 0x03,
-  CLASS_EXTENSION  = 0x04,
-  CLASS_ERROR      = 0x05
+  CLASS_NOTE = DiagnosticIDs::CLASS_NOTE,
+  CLASS_REMARK = DiagnosticIDs::CLASS_REMARK,
+  CLASS_WARNING = DiagnosticIDs::CLASS_WARNING,
+  CLASS_EXTENSION = DiagnosticIDs::CLASS_EXTENSION,
+  CLASS_ERROR = DiagnosticIDs::CLASS_ERROR,
 };
 
 struct StaticDiagInfoRec {
@@ -229,11 +228,60 @@ CATEGORY(INSTALLAPI, REFACTORING)
   return Found;
 }
 
-DiagnosticMapping DiagnosticIDs::getDefaultMapping(unsigned DiagID) {
+//===----------------------------------------------------------------------===//
+// Custom Diagnostic information
+//===----------------------------------------------------------------------===//
+
+namespace clang {
+namespace diag {
+using CustomDiagDesc = DiagnosticIDs::CustomDiagDesc;
+class CustomDiagInfo {
+  std::vector<CustomDiagDesc> DiagInfo;
+  std::map<CustomDiagDesc, unsigned> DiagIDs;
+  std::map<diag::Group, std::vector<unsigned>> GroupToDiags;
+
+public:
+  /// getDescription - Return the description of the specified custom
+  /// diagnostic.
+  const CustomDiagDesc &getDescription(unsigned DiagID) const {
+    assert(DiagID - DIAG_UPPER_LIMIT < DiagInfo.size() &&
+           "Invalid diagnostic ID");
+    return DiagInfo[DiagID - DIAG_UPPER_LIMIT];
+  }
+
+  unsigned getOrCreateDiagID(DiagnosticIDs::CustomDiagDesc D) {
+    // Check to see if it already exists.
+    std::map<CustomDiagDesc, unsigned>::iterator I = DiagIDs.lower_bound(D);
+    if (I != DiagIDs.end() && I->first == D)
+      return I->second;
+
+    // If not, assign a new ID.
+    unsigned ID = DiagInfo.size() + DIAG_UPPER_LIMIT;
+    DiagIDs.insert(std::make_pair(D, ID));
+    DiagInfo.push_back(D);
+    if (auto Group = D.GetGroup())
+      GroupToDiags[*Group].emplace_back(ID);
+    return ID;
+  }
+
+  ArrayRef<unsigned> getDiagsInGroup(diag::Group G) const {
+    if (auto Diags = GroupToDiags.find(G); Diags != GroupToDiags.end())
+      return Diags->second;
+    return {};
+  }
+};
+
+} // namespace diag
+} // namespace clang
+
+DiagnosticMapping DiagnosticIDs::getDefaultMapping(unsigned DiagID) const {
   DiagnosticMapping Info = DiagnosticMapping::Make(
       diag::Severity::Fatal, /*IsUser=*/false, /*IsPragma=*/false);
 
-  if (const StaticDiagInfoRec *StaticInfo = GetDiagInfo(DiagID)) {
+  if (IsCustomDiag(DiagID)) {
+    Info.setSeverity(
+        CustomDiagInfo->getDescription(DiagID).GetDefaultSeverity());
+  } else if (const StaticDiagInfoRec *StaticInfo = GetDiagInfo(DiagID)) {
     Info.setSeverity((diag::Severity)StaticInfo->DefaultSeverity);
 
     if (StaticInfo->WarnNoWerror) {
@@ -246,6 +294,22 @@ DiagnosticMapping DiagnosticIDs::getDefaultMapping(unsigned DiagID) {
   return Info;
 }
 
+void DiagnosticIDs::initCustomDiagMapping(DiagnosticMapping &Mapping,
+                                          unsigned DiagID) {
+  assert(IsCustomDiag(DiagID));
+  const auto &Diag = CustomDiagInfo->getDescription(DiagID);
+  if (auto Group = Diag.GetGroup()) {
+    GroupInfo GroupInfo = GroupInfos[static_cast<size_t>(*Group)];
+    if (static_cast<diag::Severity>(GroupInfo.Severity) != diag::Severity())
+      Mapping.setSeverity(static_cast<diag::Severity>(GroupInfo.Severity));
+    Mapping.setNoWarningAsError(GroupInfo.HasNoWarningAsError);
+  } else {
+    Mapping.setSeverity(Diag.GetDefaultSeverity());
+    Mapping.setNoWarningAsError(true);
+    Mapping.setNoErrorAsFatal(true);
+  }
+}
+
 /// getCategoryNumberForDiag - Return the category number that a specified
 /// DiagID belongs to, or 0 if no category.
 unsigned DiagnosticIDs::getCategoryNumberForDiag(unsigned DiagID) {
@@ -303,61 +367,6 @@ bool DiagnosticIDs::isDeferrable(unsigned DiagID) {
   return false;
 }
 
-/// getBuiltinDiagClass - Return the class field of the diagnostic.
-///
-static unsigned getBuiltinDiagClass(unsigned DiagID) {
-  if (const StaticDiagInfoRec *Info = GetDiagInfo(DiagID))
-    return Info->Class;
-  return ~0U;
-}
-
-//===----------------------------------------------------------------------===//
-// Custom Diagnostic information
-//===----------------------------------------------------------------------===//
-
-namespace clang {
-  namespace diag {
-    class CustomDiagInfo {
-      typedef std::pair<DiagnosticIDs::Level, std::string> DiagDesc;
-      std::vector<DiagDesc> DiagInfo;
-      std::map<DiagDesc, unsigned> DiagIDs;
-    public:
-
-      /// getDescription - Return the description of the specified custom
-      /// diagnostic.
-      StringRef getDescription(unsigned DiagID) const {
-        assert(DiagID - DIAG_UPPER_LIMIT < DiagInfo.size() &&
-               "Invalid diagnostic ID");
-        return DiagInfo[DiagID-DIAG_UPPER_LIMIT].second;
-      }
-
-      /// getLevel - Return the level of the specified custom diagnostic.
-      DiagnosticIDs::Level getLevel(unsigned DiagID) const {
-        assert(DiagID - DIAG_UPPER_LIMIT < DiagInfo.size() &&
-               "Invalid diagnostic ID");
-        return DiagInfo[DiagID-DIAG_UPPER_LIMIT].first;
-      }
-
-      unsigned getOrCreateDiagID(DiagnosticIDs::Level L, StringRef Message,
-                                 DiagnosticIDs &Diags) {
-        DiagDesc D(L, std::string(Message));
-        // Check to see if it already exists.
-        std::map<DiagDesc, unsigned>::iterator I = DiagIDs.lower_bound(D);
-        if (I != DiagIDs.end() && I->first == D)
-          return I->second;
-
-        // If not, assign a new ID.
-        unsigned ID = DiagInfo.size()+DIAG_UPPER_LIMIT;
-        DiagIDs.insert(std::make_pair(D, ID));
-        DiagInfo.push_back(D);
-        return ID;
-      }
-    };
-
-  } // end diag namespace
-} // end clang namespace
-
-
 //===----------------------------------------------------------------------===//
 // Common Diagnostic implementation
 //===----------------------------------------------------------------------===//
@@ -372,38 +381,32 @@ DiagnosticIDs::~DiagnosticIDs() {}
 ///
 /// \param FormatString A fixed diagnostic format string that will be hashed and
 /// mapped to a unique DiagID.
-unsigned DiagnosticIDs::getCustomDiagID(Level L, StringRef FormatString) {
+unsigned DiagnosticIDs::getCustomDiagID(CustomDiagDesc Diag) {
   if (!CustomDiagInfo)
     CustomDiagInfo.reset(new diag::CustomDiagInfo());
-  return CustomDiagInfo->getOrCreateDiagID(L, FormatString, *this);
+  return CustomDiagInfo->getOrCreateDiagID(Diag);
 }
 
-
-/// isBuiltinWarningOrExtension - Return true if the unmapped diagnostic
-/// level of the specified diagnostic ID is a Warning or Extension.
-/// This only works on builtin diagnostics, not custom ones, and is not legal to
-/// call on NOTEs.
-bool DiagnosticIDs::isBuiltinWarningOrExtension(unsigned DiagID) {
-  return DiagID < diag::DIAG_UPPER_LIMIT &&
-         getBuiltinDiagClass(DiagID) != CLASS_ERROR;
+bool DiagnosticIDs::isWarningOrExtension(unsigned DiagID) const {
+  return DiagID < diag::DIAG_UPPER_LIMIT
+             ? getDiagClass(DiagID) != CLASS_ERROR
+             : CustomDiagInfo->getDescription(DiagID).GetClass() != CLASS_ERROR;
 }
 
 /// Determine whether the given built-in diagnostic ID is a
 /// Note.
-bool DiagnosticIDs::isBuiltinNote(unsigned DiagID) {
-  return DiagID < diag::DIAG_UPPER_LIMIT &&
-    getBuiltinDiagClass(DiagID) == CLASS_NOTE;
+bool DiagnosticIDs::isNote(unsigned DiagID) const {
+  return DiagID < diag::DIAG_UPPER_LIMIT && getDiagClass(DiagID) == CLASS_NOTE;
 }
 
-/// isBuiltinExtensionDiag - Determine whether the given built-in diagnostic
+/// isExtensionDiag - Determine whether the given built-in diagnostic
 /// ID is for an extension of some sort.  This also returns EnabledByDefault,
 /// which is set to indicate whether the diagnostic is ignored by default (in
 /// which case -pedantic enables it) or treated as a warning/error by default.
 ///
-bool DiagnosticIDs::isBuiltinExtensionDiag(unsigned DiagID,
-                                        bool &EnabledByDefault) {
-  if (DiagID >= diag::DIAG_UPPER_LIMIT ||
-      getBuiltinDiagClass(DiagID) != CLASS_EXTENSION)
+bool DiagnosticIDs::isExtensionDiag(unsigned DiagID,
+                                    bool &EnabledByDefault) const {
+  if (IsCustomDiag(DiagID) || getDiagClass(DiagID) != CLASS_EXTENSION)
     return false;
 
   EnabledByDefault =
@@ -411,10 +414,7 @@ bool DiagnosticIDs::isBuiltinExtensionDiag(unsigned DiagID,
   return true;
 }
 
-bool DiagnosticIDs::isDefaultMappingAsError(unsigned DiagID) {
-  if (DiagID >= diag::DIAG_UPPER_LIMIT)
-    return false;
-
+bool DiagnosticIDs::isDefaultMappingAsError(unsigned DiagID) const {
   return getDefaultMapping(DiagID).getSeverity() >= diag::Severity::Error;
 }
 
@@ -424,7 +424,7 @@ StringRef DiagnosticIDs::getDescription(unsigned DiagID) const {
   if (const StaticDiagInfoRec *Info = GetDiagInfo(DiagID))
     return Info->getDescription();
   assert(CustomDiagInfo && "Invalid CustomDiagInfo");
-  return CustomDiagInfo->getDescription(DiagID);
+  return CustomDiagInfo->getDescription(DiagID).GetDescription();
 }
 
 static DiagnosticIDs::Level toLevel(diag::Severity SV) {
@@ -449,13 +449,7 @@ static DiagnosticIDs::Level toLevel(diag::Severity SV) {
 DiagnosticIDs::Level
 DiagnosticIDs::getDiagnosticLevel(unsigned DiagID, SourceLocation Loc,
                                   const DiagnosticsEngine &Diag) const {
-  // Handle custom diagnostics, which cannot be mapped.
-  if (DiagID >= diag::DIAG_UPPER_LIMIT) {
-    assert(CustomDiagInfo && "Invalid CustomDiagInfo");
-    return CustomDiagInfo->getLevel(DiagID);
-  }
-
-  unsigned DiagClass = getBuiltinDiagClass(DiagID);
+  unsigned DiagClass = getDiagClass(DiagID);
   if (DiagClass == CLASS_NOTE) return DiagnosticIDs::Note;
   return toLevel(getDiagnosticSeverity(DiagID, Loc, Diag));
 }
@@ -469,7 +463,8 @@ DiagnosticIDs::getDiagnosticLevel(unsigned DiagID, SourceLocation Loc,
 diag::Severity
 DiagnosticIDs::getDiagnosticSeverity(unsigned DiagID, SourceLocation Loc,
                                      const DiagnosticsEngine &Diag) const {
-  assert(getBuiltinDiagClass(DiagID) != CLASS_NOTE);
+  bool IsCustomDiag = DiagnosticIDs::IsCustomDiag(DiagID);
+  assert(getDiagClass(DiagID) != CLASS_NOTE);
 
   // Specific non-error diagnostics may be mapped to various levels from ignored
   // to error.  Errors can only be mapped to fatal.
@@ -477,7 +472,7 @@ DiagnosticIDs::getDiagnosticSeverity(unsigned DiagID, SourceLocation Loc,
 
   // Get the mapping information, or compute it lazily.
   DiagnosticsEngine::DiagState *State = Diag.GetDiagStateForLoc(Loc);
-  DiagnosticMapping &Mapping = State->getOrAddMapping((diag::kind)DiagID);
+  DiagnosticMapping Mapping = State->getOrAddMapping((diag::kind)DiagID);
 
   // TODO: Can a null severity really get here?
   if (Mapping.getSeverity() != diag::Severity())
@@ -485,14 +480,15 @@ DiagnosticIDs::getDiagnosticSeverity(unsigned DiagID, SourceLocation Loc,
 
   // Upgrade ignored diagnostics if -Weverything is enabled.
   if (State->EnableAllWarnings && Result == diag::Severity::Ignored &&
-      !Mapping.isUser() && getBuiltinDiagClass(DiagID) != CLASS_REMARK)
+      !Mapping.isUser() &&
+      (IsCustomDiag || getDiagClass(DiagID) != CLASS_REMARK))
     Result = diag::Severity::Warning;
 
   // Ignore -pedantic diagnostics inside __extension__ blocks.
   // (The diagnostics controlled by -pedantic are the extension diagnostics
   // that are not enabled by default.)
   bool EnabledByDefault = false;
-  bool IsExtensionDiag = isBuiltinExtensionDiag(DiagID, EnabledByDefault);
+  bool IsExtensionDiag = isExtensionDiag(DiagID, EnabledByDefault);
   if (Diag.AllExtensionsSilenced && IsExtensionDiag && !EnabledByDefault)
     return diag::Severity::Ignored;
 
@@ -510,10 +506,12 @@ DiagnosticIDs::getDiagnosticSeverity(unsigned DiagID, SourceLocation Loc,
   // as well as disabling all messages which are currently mapped to Warning
   // (whether by default or downgraded from Error via e.g. -Wno-error or #pragma
   // diagnostic.)
+  // FIXME: Should -w be ignored for custom warnings without a group?
   if (State->IgnoreAllWarnings) {
-    if (Result == diag::Severity::Warning ||
-        (Result >= diag::Severity::Error &&
-         !isDefaultMappingAsError((diag::kind)DiagID)))
+    if ((!IsCustomDiag || CustomDiagInfo->getDescription(DiagID).GetGroup()) &&
+        (Result == diag::Severity::Warning ||
+         (Result >= diag::Severity::Error &&
+          !isDefaultMappingAsError((diag::kind)DiagID))))
       return diag::Severity::Ignored;
   }
 
@@ -541,9 +539,11 @@ DiagnosticIDs::getDiagnosticSeverity(unsigned DiagID, SourceLocation Loc,
     return Result;
 
   const auto &SM = Diag.getSourceManager();
-  // Custom diagnostics always are emitted in system headers.
+
   bool ShowInSystemHeader =
-      !GetDiagInfo(DiagID) || GetDiagInfo(DiagID)->WarnShowInSystemHeader;
+      IsCustomDiag
+          ? CustomDiagInfo->getDescription(DiagID).ShouldShowInSystemHeader()
+          : !GetDiagInfo(DiagID) || GetDiagInfo(DiagID)->WarnShowInSystemHeader;
 
   // If we are in a system header, we ignore it. We look at the diagnostic class
   // because we also want to ignore extensions and warnings in -Werror and
@@ -566,6 +566,15 @@ DiagnosticIDs::getDiagnosticSeverity(unsigned DiagID, SourceLocation Loc,
   return Result;
 }
 
+DiagnosticIDs::Class DiagnosticIDs::getDiagClass(unsigned DiagID) const {
+  if (IsCustomDiag(DiagID))
+    return Class(CustomDiagInfo->getDescription(DiagID).GetClass());
+
+  if (const StaticDiagInfoRec *Info = GetDiagInfo(DiagID))
+    return Class(Info->Class);
+  return CLASS_INVALID;
+}
+
 #define GET_DIAG_ARRAYS
 #include "clang/Basic/DiagnosticGroups.inc"
 #undef GET_DIAG_ARRAYS
@@ -607,7 +616,12 @@ DiagnosticIDs::getGroupForWarningOption(StringRef Name) {
   return static_cast<diag::Group>(Found - OptionTable);
 }
 
-std::optional<diag::Group> DiagnosticIDs::getGroupForDiag(unsigned DiagID) {
+std::optional<diag::Group>
+DiagnosticIDs::getGroupForDiag(unsigned DiagID) const {
+  if (IsCustomDiag(DiagID)) {
+    assert(CustomDiagInfo);
+    return CustomDiagInfo->getDescription(DiagID).GetGroup();
+  }
   if (const StaticDiagInfoRec *Info = GetDiagInfo(DiagID))
     return static_cast<diag::Group>(Info->getOptionGroupIndex());
   return std::nullopt;
@@ -639,7 +653,8 @@ std::vector<std::string> DiagnosticIDs::getDiagnosticFlags() {
 /// were filtered out due to having the wrong flavor.
 static bool getDiagnosticsInGroup(diag::Flavor Flavor,
                                   const WarningOption *Group,
-                                  SmallVectorImpl<diag::kind> &Diags) {
+                                  SmallVectorImpl<diag::kind> &Diags,
+                                  diag::CustomDiagInfo *CustomDiagInfo) {
   // An empty group is considered to be a warning group: we have empty groups
   // for GCC compatibility, and GCC does not have remarks.
   if (!Group->Members && !Group->SubGroups)
@@ -658,9 +673,14 @@ static bool getDiagnosticsInGroup(diag::Flavor Flavor,
 
   // Add the members of the subgroups.
   const int16_t *SubGroups = DiagSubGroups + Group->SubGroups;
-  for (; *SubGroups != (int16_t)-1; ++SubGroups)
+  for (; *SubGroups != (int16_t)-1; ++SubGroups) {
+    if (CustomDiagInfo)
+      llvm::copy(
+          CustomDiagInfo->getDiagsInGroup(static_cast<diag::Group>(*SubGroups)),
+          std::back_inserter(Diags));
     NotFound &= getDiagnosticsInGroup(Flavor, &OptionTable[(short)*SubGroups],
-                                      Diags);
+                                      Diags, CustomDiagInfo);
+  }
 
   return NotFound;
 }
@@ -668,12 +688,49 @@ static bool getDiagnosticsInGroup(diag::Flavor Flavor,
 bool
 DiagnosticIDs::getDiagnosticsInGroup(diag::Flavor Flavor, StringRef Group,
                                      SmallVectorImpl<diag::kind> &Diags) const {
-  if (std::optional<diag::Group> G = getGroupForWarningOption(Group))
-    return ::getDiagnosticsInGroup(
-        Flavor, &OptionTable[static_cast<unsigned>(*G)], Diags);
+  if (std::optional<diag::Group> G = getGroupForWarningOption(Group)) {
+    if (CustomDiagInfo)
+      llvm::copy(CustomDiagInfo->getDiagsInGroup(*G),
+                 std::back_inserter(Diags));
+    return ::getDiagnosticsInGroup(Flavor,
+                                   &OptionTable[static_cast<unsigned>(*G)],
+                                   Diags, CustomDiagInfo.get());
+  }
   return true;
 }
 
+template <class Func>
+static void forEachSubGroupImpl(const WarningOption *Group, Func func) {
+  for (const int16_t *SubGroups = DiagSubGroups + Group->SubGroups;
+       *SubGroups != -1; ++SubGroups) {
+    func(static_cast<size_t>(*SubGroups));
+    forEachSubGroupImpl(&OptionTable[*SubGroups], std::move(func));
+  }
+}
+
+template <class Func>
+static void forEachSubGroup(diag::Group Group, Func func) {
+  const WarningOption *WarningOpt = &OptionTable[static_cast<size_t>(Group)];
+  func(static_cast<size_t>(Group));
+  ::forEachSubGroupImpl(WarningOpt, std::move(func));
+}
+
+void DiagnosticIDs::setGroupSeverity(StringRef Group, diag::Severity Sev) {
+  if (std::optional<diag::Group> G = getGroupForWarningOption(Group)) {
+    ::forEachSubGroup(*G, [&](size_t SubGroup) {
+      GroupInfos[SubGroup].Severity = static_cast<unsigned>(Sev);
+    });
+  }
+}
+
+void DiagnosticIDs::setGroupNoWarningsAsError(StringRef Group, bool Val) {
+  if (std::optional<diag::Group> G = getGroupForWarningOption(Group)) {
+    ::forEachSubGroup(*G, [&](size_t SubGroup) {
+      GroupInfos[static_cast<size_t>(*G)].HasNoWarningAsError = Val;
+    });
+  }
+}
+
 void DiagnosticIDs::getAllDiagnostics(diag::Flavor Flavor,
                                       std::vector<diag::kind> &Diags) {
   for (unsigned i = 0; i != StaticDiagInfoSize; ++i)
@@ -696,7 +753,7 @@ StringRef DiagnosticIDs::getNearestOption(diag::Flavor Flavor,
 
     // Don't suggest groups that are not of this kind.
     llvm::SmallVector<diag::kind, 8> Diags;
-    if (::getDiagnosticsInGroup(Flavor, &O, Diags) || Diags.empty())
+    if (::getDiagnosticsInGroup(Flavor, &O, Diags, nullptr) || Diags.empty())
       continue;
 
     if (Distance == BestDistance) {
@@ -810,14 +867,8 @@ void DiagnosticIDs::EmitDiag(DiagnosticsEngine &Diag,
 }
 
 bool DiagnosticIDs::isUnrecoverable(unsigned DiagID) const {
-  if (DiagID >= diag::DIAG_UPPER_LIMIT) {
-    assert(CustomDiagInfo && "Invalid CustomDiagInfo");
-    // Custom diagnostics.
-    return CustomDiagInfo->getLevel(DiagID) >= DiagnosticIDs::Error;
-  }
-
   // Only errors may be unrecoverable.
-  if (getBuiltinDiagClass(DiagID) < CLASS_ERROR)
+  if (getDiagClass(DiagID) < CLASS_ERROR)
     return false;
 
   if (DiagID == diag::err_unavailable ||
diff --git a/clang/lib/Frontend/LogDiagnosticPrinter.cpp b/clang/lib/Frontend/LogDiagnosticPrinter.cpp
index 469d1c2..4e963af 100644
--- a/clang/lib/Frontend/LogDiagnosticPrinter.cpp
+++ b/clang/lib/Frontend/LogDiagnosticPrinter.cpp
@@ -129,7 +129,8 @@ void LogDiagnosticPrinter::HandleDiagnostic(DiagnosticsEngine::Level Level,
   DE.DiagnosticLevel = Level;
 
   DE.WarningOption =
-      std::string(DiagnosticIDs::getWarningOptionForDiag(DE.DiagnosticID));
+      std::string(Info.getDiags()->getDiagnosticIDs()->getWarningOptionForDiag(
+          DE.DiagnosticID));
 
   // Format the message.
   SmallString<100> MessageStr;
@@ -160,4 +161,3 @@ void LogDiagnosticPrinter::HandleDiagnostic(DiagnosticsEngine::Level Level,
   // Record the diagnostic entry.
   Entries.push_back(DE);
 }
-
diff --git a/clang/lib/Frontend/SerializedDiagnosticPrinter.cpp b/clang/lib/Frontend/SerializedDiagnosticPrinter.cpp
index 1313342..02aa3e8 100644
--- a/clang/lib/Frontend/SerializedDiagnosticPrinter.cpp
+++ b/clang/lib/Frontend/SerializedDiagnosticPrinter.cpp
@@ -202,7 +202,7 @@ private:
 
   /// Emit the string information for diagnostic flags.
   unsigned getEmitDiagnosticFlag(DiagnosticsEngine::Level DiagLevel,
-                                 unsigned DiagID = 0);
+                                 const Diagnostic *Diag = nullptr);
 
   unsigned getEmitDiagnosticFlag(StringRef DiagName);
 
@@ -536,11 +536,13 @@ unsigned SDiagsWriter::getEmitCategory(unsigned int category) {
 }
 
 unsigned SDiagsWriter::getEmitDiagnosticFlag(DiagnosticsEngine::Level DiagLevel,
-                                             unsigned DiagID) {
-  if (DiagLevel == DiagnosticsEngine::Note)
+                                             const Diagnostic *Diag) {
+  if (!Diag || DiagLevel == DiagnosticsEngine::Note)
     return 0; // No flag for notes.
 
-  StringRef FlagName = DiagnosticIDs::getWarningOptionForDiag(DiagID);
+  StringRef FlagName =
+      Diag->getDiags()->getDiagnosticIDs()->getWarningOptionForDiag(
+          Diag->getID());
   return getEmitDiagnosticFlag(FlagName);
 }
 
@@ -655,7 +657,7 @@ void SDiagsWriter::EmitDiagnosticMessage(FullSourceLoc Loc, PresumedLoc PLoc,
     unsigned DiagID = DiagnosticIDs::getCategoryNumberForDiag(Info->getID());
     Record.push_back(getEmitCategory(DiagID));
     // Emit the diagnostic flag string lazily and get the mapped ID.
-    Record.push_back(getEmitDiagnosticFlag(Level, Info->getID()));
+    Record.push_back(getEmitDiagnosticFlag(Level, Info));
   } else {
     Record.push_back(getEmitCategory());
     Record.push_back(getEmitDiagnosticFlag(Level));
diff --git a/clang/lib/Frontend/TextDiagnosticPrinter.cpp b/clang/lib/Frontend/TextDiagnosticPrinter.cpp
index dac5c44..28f7218 100644
--- a/clang/lib/Frontend/TextDiagnosticPrinter.cpp
+++ b/clang/lib/Frontend/TextDiagnosticPrinter.cpp
@@ -70,13 +70,17 @@ static void printDiagnosticOptions(raw_ostream &OS,
     // flag it as such. Note that diagnostics could also have been mapped by a
     // pragma, but we don't currently have a way to distinguish this.
     if (Level == DiagnosticsEngine::Error &&
-        DiagnosticIDs::isBuiltinWarningOrExtension(Info.getID()) &&
-        !DiagnosticIDs::isDefaultMappingAsError(Info.getID())) {
+        Info.getDiags()->getDiagnosticIDs()->isWarningOrExtension(
+            Info.getID()) &&
+        !Info.getDiags()->getDiagnosticIDs()->isDefaultMappingAsError(
+            Info.getID())) {
       OS << " [-Werror";
       Started = true;
     }
 
-    StringRef Opt = DiagnosticIDs::getWarningOptionForDiag(Info.getID());
+    StringRef Opt =
+        Info.getDiags()->getDiagnosticIDs()->getWarningOptionForDiag(
+            Info.getID());
     if (!Opt.empty()) {
       OS << (Started ? "," : " [")
          << (Level == DiagnosticsEngine::Remark ? "-R" : "-W") << Opt;
diff --git a/clang/lib/Sema/Sema.cpp b/clang/lib/Sema/Sema.cpp
index abb46d3..9507d76 100644
--- a/clang/lib/Sema/Sema.cpp
+++ b/clang/lib/Sema/Sema.cpp
@@ -1679,7 +1679,7 @@ void Sema::EmitDiagnostic(unsigned DiagID, const DiagnosticBuilder &DB) {
   // that is different from the last template instantiation where
   // we emitted an error, print a template instantiation
   // backtrace.
-  if (!DiagnosticIDs::isBuiltinNote(DiagID))
+  if (!Diags.getDiagnosticIDs()->isNote(DiagID))
     PrintContextStack();
 }
 
@@ -1693,7 +1693,8 @@ bool Sema::hasUncompilableErrorOccurred() const {
   if (Loc == DeviceDeferredDiags.end())
     return false;
   for (auto PDAt : Loc->second) {
-    if (DiagnosticIDs::isDefaultMappingAsError(PDAt.second.getDiagID()))
+    if (Diags.getDiagnosticIDs()->isDefaultMappingAsError(
+            PDAt.second.getDiagID()))
       return true;
   }
   return false;
diff --git a/clang/lib/Sema/SemaCUDA.cpp b/clang/lib/Sema/SemaCUDA.cpp
index 35f28bf..0e1bf72 100644
--- a/clang/lib/Sema/SemaCUDA.cpp
+++ b/clang/lib/Sema/SemaCUDA.cpp
@@ -833,7 +833,7 @@ SemaBase::SemaDiagnosticBuilder SemaCUDA::DiagIfDeviceCode(SourceLocation Loc,
       if (!getLangOpts().CUDAIsDevice)
         return SemaDiagnosticBuilder::K_Nop;
       if (SemaRef.IsLastErrorImmediate &&
-          getDiagnostics().getDiagnosticIDs()->isBuiltinNote(DiagID))
+          getDiagnostics().getDiagnosticIDs()->isNote(DiagID))
         return SemaDiagnosticBuilder::K_Immediate;
       return (SemaRef.getEmissionStatus(CurFunContext) ==
               Sema::FunctionEmissionStatus::Emitted)
@@ -864,7 +864,7 @@ Sema::SemaDiagnosticBuilder SemaCUDA::DiagIfHostCode(SourceLocation Loc,
       if (getLangOpts().CUDAIsDevice)
         return SemaDiagnosticBuilder::K_Nop;
       if (SemaRef.IsLastErrorImmediate &&
-          getDiagnostics().getDiagnosticIDs()->isBuiltinNote(DiagID))
+          getDiagnostics().getDiagnosticIDs()->isNote(DiagID))
         return SemaDiagnosticBuilder::K_Immediate;
       return (SemaRef.getEmissionStatus(CurFunContext) ==
               Sema::FunctionEmissionStatus::Emitted)
diff --git a/clang/lib/Sema/SemaDeclAttr.cpp b/clang/lib/Sema/SemaDeclAttr.cpp
index c2d82b9..9d7d225 100644
--- a/clang/lib/Sema/SemaDeclAttr.cpp
+++ b/clang/lib/Sema/SemaDeclAttr.cpp
@@ -879,22 +879,38 @@ static void handleDiagnoseIfAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
   if (!checkFunctionConditionAttr(S, D, AL, Cond, Msg))
     return;
 
-  StringRef DiagTypeStr;
-  if (!S.checkStringLiteralArgumentAttr(AL, 2, DiagTypeStr))
+  StringRef DefaultSevStr;
+  if (!S.checkStringLiteralArgumentAttr(AL, 2, DefaultSevStr))
     return;
 
-  DiagnoseIfAttr::DiagnosticType DiagType;
-  if (!DiagnoseIfAttr::ConvertStrToDiagnosticType(DiagTypeStr, DiagType)) {
+  DiagnoseIfAttr::DefaultSeverity DefaultSev;
+  if (!DiagnoseIfAttr::ConvertStrToDefaultSeverity(DefaultSevStr, DefaultSev)) {
     S.Diag(AL.getArgAsExpr(2)->getBeginLoc(),
            diag::err_diagnose_if_invalid_diagnostic_type);
     return;
   }
 
+  StringRef WarningGroup;
+  SmallVector<StringRef, 2> Options;
+  if (AL.getNumArgs() > 3) {
+    if (!S.checkStringLiteralArgumentAttr(AL, 3, WarningGroup))
+      return;
+    if (WarningGroup.empty() ||
+        !S.getDiagnostics().getDiagnosticIDs()->getGroupForWarningOption(
+            WarningGroup)) {
+      S.Diag(AL.getArgAsExpr(3)->getBeginLoc(),
+             diag::err_diagnose_if_unknown_warning)
+          << WarningGroup;
+      return;
+    }
+  }
+
   bool ArgDependent = false;
   if (const auto *FD = dyn_cast<FunctionDecl>(D))
     ArgDependent = ArgumentDependenceChecker(FD).referencesArgs(Cond);
   D->addAttr(::new (S.Context) DiagnoseIfAttr(
-      S.Context, AL, Cond, Msg, DiagType, ArgDependent, cast<NamedDecl>(D)));
+      S.Context, AL, Cond, Msg, DefaultSev, WarningGroup, ArgDependent,
+      cast<NamedDecl>(D)));
 }
 
 static void handleNoBuiltinAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
diff --git a/clang/lib/Sema/SemaOverload.cpp b/clang/lib/Sema/SemaOverload.cpp
index 6ae9c51..776dba8 100644
--- a/clang/lib/Sema/SemaOverload.cpp
+++ b/clang/lib/Sema/SemaOverload.cpp
@@ -7377,8 +7377,10 @@ static bool diagnoseDiagnoseIfAttrsWith(Sema &S, const NamedDecl *ND,
     return false;
 
   auto WarningBegin = std::stable_partition(
-      Attrs.begin(), Attrs.end(),
-      [](const DiagnoseIfAttr *DIA) { return DIA->isError(); });
+      Attrs.begin(), Attrs.end(), [](const DiagnoseIfAttr *DIA) {
+        return DIA->getDefaultSeverity() == DiagnoseIfAttr::DS_error &&
+               DIA->getWarningGroup().empty();
+      });
 
   // Note that diagnose_if attributes are late-parsed, so they appear in the
   // correct order (unlike enable_if attributes).
@@ -7392,11 +7394,32 @@ static bool diagnoseDiagnoseIfAttrsWith(Sema &S, const NamedDecl *ND,
     return true;
   }
 
+  auto ToSeverity = [](DiagnoseIfAttr::DefaultSeverity Sev) {
+    switch (Sev) {
+    case DiagnoseIfAttr::DS_warning:
+      return diag::Severity::Warning;
+    case DiagnoseIfAttr::DS_error:
+      return diag::Severity::Error;
+    }
+    llvm_unreachable("Fully covered switch above!");
+  };
+
   for (const auto *DIA : llvm::make_range(WarningBegin, Attrs.end()))
     if (IsSuccessful(DIA)) {
-      S.Diag(Loc, diag::warn_diagnose_if_succeeded) << DIA->getMessage();
-      S.Diag(DIA->getLocation(), diag::note_from_diagnose_if)
-          << DIA->getParent() << DIA->getCond()->getSourceRange();
+      if (DIA->getWarningGroup().empty() &&
+          DIA->getDefaultSeverity() == DiagnoseIfAttr::DS_warning) {
+        S.Diag(Loc, diag::warn_diagnose_if_succeeded) << DIA->getMessage();
+        S.Diag(DIA->getLocation(), diag::note_from_diagnose_if)
+            << DIA->getParent() << DIA->getCond()->getSourceRange();
+      } else {
+        auto DiagGroup = S.Diags.getDiagnosticIDs()->getGroupForWarningOption(
+            DIA->getWarningGroup());
+        assert(DiagGroup);
+        auto DiagID = S.Diags.getDiagnosticIDs()->getCustomDiagID(
+            {ToSeverity(DIA->getDefaultSeverity()), "%0",
+             DiagnosticIDs::CLASS_WARNING, false, false, *DiagGroup});
+        S.Diag(Loc, DiagID) << DIA->getMessage();
+      }
     }
 
   return false;
diff --git a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
index ebe2dd9..16a7049 100644
--- a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -284,7 +284,8 @@ static void instantiateDependentDiagnoseIfAttr(
   if (Cond)
     New->addAttr(new (S.getASTContext()) DiagnoseIfAttr(
         S.getASTContext(), *DIA, Cond, DIA->getMessage(),
-        DIA->getDiagnosticType(), DIA->getArgDependent(), New));
+        DIA->getDefaultSeverity(), DIA->getWarningGroup(),
+        DIA->getArgDependent(), New));
 }
 
 // Constructs and adds to New a new instance of CUDALaunchBoundsAttr using
diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
index 08801d2..f524251 100644
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/clang/lib/Serialization/ASTReader.cpp
@@ -6864,7 +6864,7 @@ void ASTReader::ReadPragmaDiagnosticMappings(DiagnosticsEngine &Diag) {
       // command line (-w, -Weverything, -Werror, ...) along with any explicit
       // -Wblah flags.
       unsigned Flags = Record[Idx++];
-      DiagState Initial;
+      DiagState Initial(*Diag.getDiagnosticIDs());
       Initial.SuppressSystemWarnings = Flags & 1; Flags >>= 1;
       Initial.ErrorsAsFatal = Flags & 1; Flags >>= 1;
       Initial.WarningsAsErrors = Flags & 1; Flags >>= 1;
diff --git a/clang/lib/Serialization/ASTWriter.cpp b/clang/lib/Serialization/ASTWriter.cpp
index a580f37..2d0fae8 100644
--- a/clang/lib/Serialization/ASTWriter.cpp
+++ b/clang/lib/Serialization/ASTWriter.cpp
@@ -3264,7 +3264,7 @@ void ASTWriter::WritePragmaDiagnosticMappings(const DiagnosticsEngine &Diag,
         // Skip default mappings. We have a mapping for every diagnostic ever
         // emitted, regardless of whether it was customized.
         if (!I.second.isPragma() &&
-            I.second == DiagnosticIDs::getDefaultMapping(I.first))
+            I.second == Diag.getDiagnosticIDs()->getDefaultMapping(I.first))
           continue;
         Mappings.push_back(I);
       }
diff --git a/clang/lib/StaticAnalyzer/Core/TextDiagnostics.cpp b/clang/lib/StaticAnalyzer/Core/TextDiagnostics.cpp
index e8cf367..79ee430 100644
--- a/clang/lib/StaticAnalyzer/Core/TextDiagnostics.cpp
+++ b/clang/lib/StaticAnalyzer/Core/TextDiagnostics.cpp
@@ -91,7 +91,6 @@ public:
                                     ? " [" + PD->getCheckerName() + "]"
                                     : "")
                                    .str();
-
       reportPiece(WarnID, PD->getLocation().asLocation(),
                   (PD->getShortDescription() + WarningMsg).str(),
                   PD->path.back()->getRanges(), PD->path.back()->getFixits());