Revert "[Clang] improve -Wstring-concatenation to warn on every missing comma in initializer lists" (llvm#154369)

Revert llvm#154018 changes due to excessive _false
positives_. The warning caused multiple benign reports in large
codebases (e.g. _Linux kernel_, _Fuchsia_, _tcpdump_). Since many of
these concatenations are intentional and follow project style rules, the
diagnostic introduced more false positives than value. This will be
revisited as a potential `clang-tidy` check instead.

Author: a-tarasyuk

clang/docs/ReleaseNotes.rst

@@ -168,8 +168,6 @@ Improvements to Clang's diagnostics
   an override of a virtual method.
 - Fixed fix-it hint for fold expressions. Clang now correctly places the suggested right
   parenthesis when diagnosing malformed fold expressions. (#GH151787)
-- ``-Wstring-concatenation`` now diagnoses every missing comma in an initializer list,
-  rather than stopping after the first. (#GH153745)
 
 - Fixed an issue where emitted format-signedness diagnostics were not associated with an appropriate
   diagnostic id. Besides being incorrect from an API standpoint, this was user visible, e.g.:

clang/lib/Sema/SemaDecl.cpp

@@ -14708,14 +14708,7 @@ void Sema::CheckCompleteVariableDeclaration(VarDecl *var) {
       isa<InitListExpr>(var->getInit())) {
     const auto *ILE = cast<InitListExpr>(var->getInit());
     unsigned NumInits = ILE->getNumInits();
-    if (NumInits > 2) {
-      auto concatenatedPartsAt = [&](unsigned Index) -> unsigned {
-        if (const Expr *E = ILE->getInit(Index))
-          if (const auto *S = dyn_cast<StringLiteral>(E->IgnoreImpCasts()))
-            return S->getNumConcatenated();
-        return 0;
-      };
-
+    if (NumInits > 2)
       for (unsigned I = 0; I < NumInits; ++I) {
         const auto *Init = ILE->getInit(I);
         if (!Init)
@@ -14728,33 +14721,35 @@ void Sema::CheckCompleteVariableDeclaration(VarDecl *var) {
         // Diagnose missing comma in string array initialization.
         // Do not warn when all the elements in the initializer are concatenated
         // together. Do not warn for macros too.
-        if (NumConcat == 2) {
-          if (SL->getBeginLoc().isMacroID())
-            continue;
-
-          unsigned L = I > 0 ? concatenatedPartsAt(I - 1) : 0;
-          unsigned R = I + 1 < NumInits ? concatenatedPartsAt(I + 1) : 0;
-
-          // Skip neighbors with multi-part concatenations.
-          if (R > 1)
-            continue;
+        if (NumConcat == 2 && !SL->getBeginLoc().isMacroID()) {
+          bool OnlyOneMissingComma = true;
+          for (unsigned J = I + 1; J < NumInits; ++J) {
+            const auto *Init = ILE->getInit(J);
+            if (!Init)
+              break;
+            const auto *SLJ = dyn_cast<StringLiteral>(Init->IgnoreImpCasts());
+            if (!SLJ || SLJ->getNumConcatenated() > 1) {
+              OnlyOneMissingComma = false;
+              break;
+            }
+          }
 
-          // Diagnose when at least one neighbor is a single literal.
-          if (R == 1 || L == 1) {
+          if (OnlyOneMissingComma) {
             SmallVector<FixItHint, 1> Hints;
-            // Insert a comma between the two tokens of this element.
-            Hints.push_back(FixItHint::CreateInsertion(
-                PP.getLocForEndOfToken(SL->getStrTokenLoc(0)), ", "));
+            for (unsigned i = 0; i < NumConcat - 1; ++i)
+              Hints.push_back(FixItHint::CreateInsertion(
+                  PP.getLocForEndOfToken(SL->getStrTokenLoc(i)), ","));
 
             Diag(SL->getStrTokenLoc(1),
                  diag::warn_concatenated_literal_array_init)
                 << Hints;
             Diag(SL->getBeginLoc(),
                  diag::note_concatenated_string_literal_silence);
           }
+          // In any case, stop now.
+          break;
         }
       }
-    }
   }
 
 

clang/test/Sema/string-concat.c

@@ -168,31 +168,3 @@ const char *extra_parens_to_suppress_warning[] = {
     "promise"),
     "shared_future"
 };
-
-const char *multiple_missing_commas1[] = {
-    "1",
-    "2"  // expected-note {{place parentheses around the string literal to silence warning}}
-    "3", // expected-warning {{suspicious concatenation of string literals in an array initialization; did you mean to separate the elements with a comma?}}
-    "4",
-    "5",
-    "6"  // expected-note {{place parentheses around the string literal to silence warning}}
-    "7", // expected-warning {{suspicious concatenation of string literals in an array initialization; did you mean to separate the elements with a comma?}}
-    "8",
-    "9",
-    "10",
-    "11",
-};
-
-const char *multiple_missing_commas2[] = {
-    "1",
-    "2"
-    "3"
-    "4"
-    "5",
-    "6"  // expected-note {{place parentheses around the string literal to silence warning}}
-    "7", // expected-warning {{suspicious concatenation of string literals in an array initialization; did you mean to separate the elements with a comma?}}
-    "8",
-    "9",
-    "10",
-    "11",
-};