[clang-tidy] Handled insertion only fixits when determining conflicts.

Handle insertion fix-its when removing incompatible errors by introducting a new EventType `ET_Insert`
This has lower prioirty than End events, but higher than begin.
Idea being If an insert is at the same place as a begin event, the insert should be processed first to reduce unnecessary conflicts.
Likewise if its at the same place as an end event, process the end event first for the same reason.

This also fixes https://bugs.llvm.org/show_bug.cgi?id=46511.

Reviewed By: aaron.ballman

Differential Revision: https://reviews.llvm.org/D82898

Author: njames93

clang-tools-extra/clang-tidy/ClangTidyDiagnosticConsumer.cpp

@@ -31,6 +31,7 @@
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/StringMap.h"
+#include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/FormatVariadic.h"
 #include "llvm/Support/Regex.h"
 #include <tuple>
@@ -590,6 +591,7 @@ void ClangTidyDiagnosticConsumer::removeIncompatibleErrors() {
     // An event can be either the begin or the end of an interval.
     enum EventType {
       ET_Begin = 1,
+      ET_Insert = 0,
       ET_End = -1,
     };
 
@@ -621,10 +623,17 @@ void ClangTidyDiagnosticConsumer::removeIncompatibleErrors() {
       //   one will be processed before, disallowing the second one, and the
       //   end point of the first one will also be processed before,
       //   disallowing the first one.
-      if (Type == ET_Begin)
+      switch (Type) {
+      case ET_Begin:
         Priority = std::make_tuple(Begin, Type, -End, -ErrorSize, ErrorId);
-      else
+        break;
+      case ET_Insert:
+        Priority = std::make_tuple(Begin, Type, -End, ErrorSize, ErrorId);
+        break;
+      case ET_End:
         Priority = std::make_tuple(End, Type, -Begin, ErrorSize, ErrorId);
+        break;
+      }
     }
 
     bool operator<(const Event &Other) const {
@@ -662,19 +671,19 @@ void ClangTidyDiagnosticConsumer::removeIncompatibleErrors() {
   }
 
   // Build events from error intervals.
-  std::map<std::string, std::vector<Event>> FileEvents;
+  llvm::StringMap<std::vector<Event>> FileEvents;
   for (unsigned I = 0; I < ErrorFixes.size(); ++I) {
     for (const auto &FileAndReplace : *ErrorFixes[I].second) {
       for (const auto &Replace : FileAndReplace.second) {
         unsigned Begin = Replace.getOffset();
         unsigned End = Begin + Replace.getLength();
-        const std::string &FilePath = std::string(Replace.getFilePath());
-        // FIXME: Handle empty intervals, such as those from insertions.
-        if (Begin == End)
-          continue;
-        auto &Events = FileEvents[FilePath];
-        Events.emplace_back(Begin, End, Event::ET_Begin, I, Sizes[I]);
-        Events.emplace_back(Begin, End, Event::ET_End, I, Sizes[I]);
+        auto &Events = FileEvents[Replace.getFilePath()];
+        if (Begin == End) {
+          Events.emplace_back(Begin, End, Event::ET_Insert, I, Sizes[I]);
+        } else {
+          Events.emplace_back(Begin, End, Event::ET_Begin, I, Sizes[I]);
+          Events.emplace_back(Begin, End, Event::ET_End, I, Sizes[I]);
+        }
       }
     }
   }
@@ -686,14 +695,20 @@ void ClangTidyDiagnosticConsumer::removeIncompatibleErrors() {
     llvm::sort(Events);
     int OpenIntervals = 0;
     for (const auto &Event : Events) {
-      if (Event.Type == Event::ET_End)
-        --OpenIntervals;
-      // This has to be checked after removing the interval from the count if it
-      // is an end event, or before adding it if it is a begin event.
-      if (OpenIntervals != 0)
-        Apply[Event.ErrorId] = false;
-      if (Event.Type == Event::ET_Begin)
-        ++OpenIntervals;
+      switch (Event.Type) {
+      case Event::ET_Begin:
+        if (OpenIntervals++ != 0)
+          Apply[Event.ErrorId] = false;
+        break;
+      case Event::ET_Insert:
+        if (OpenIntervals != 0)
+          Apply[Event.ErrorId] = false;
+        break;
+      case Event::ET_End:
+        if (--OpenIntervals != 0)
+          Apply[Event.ErrorId] = false;
+        break;
+      }
     }
     assert(OpenIntervals == 0 && "Amount of begin/end points doesn't match");
   }

clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines-init-variables-conflict.cpp

@@ -0,0 +1,15 @@
+// RUN: %check_clang_tidy %s cppcoreguidelines-init-variables,readability-isolate-declaration %t
+
+void foo() {
+  int A, B, C;
+  // CHECK-MESSAGES-DAG: :[[@LINE-1]]:7: warning: variable 'A' is not initialized
+  // CHECK-MESSAGES-DAG: :[[@LINE-2]]:10: warning: variable 'B' is not initialized
+  // CHECK-MESSAGES-DAG: :[[@LINE-3]]:13: warning: variable 'C' is not initialized
+  // CHECK-MESSAGES-DAG: :[[@LINE-4]]:3: warning: multiple declarations in a single statement reduces readability
+
+  // Only the isolate declarations fix-it should be applied
+
+  //      CHECK-FIXES: int A;
+  // CHECK-FIXES-NEXT: int B;
+  // CHECK-FIXES-NEXT: int C;
+}