[clang-tools-extra] [clang-reorder-fields] Prevent rewriting unsupported cases (PR #142149)

[Alexander Shaposhnikov via cfe-commits]

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@@ -50,6 +51,63 @@ static const RecordDecl *findDefinition(StringRef RecordName,
   return selectFirst<RecordDecl>("recordDecl", Results);
 }
 
+static bool isSafeToRewrite(const RecordDecl *Decl, const ASTContext &Context) {
+  // All following checks expect at least one field declaration.
+  if (Decl->field_empty())
+    return true;
+
+  // Don't attempt to rewrite if there is a declaration like 'int a, b;'.
+  SourceLocation LastTypeLoc;
+  for (const auto &Field : Decl->fields()) {
+    SourceLocation TypeLoc =
+        Field->getTypeSourceInfo()->getTypeLoc().getBeginLoc();
+    if (LastTypeLoc.isValid() && TypeLoc == LastTypeLoc)
+      return false;
+    LastTypeLoc = TypeLoc;
+  }
+
+  // Don't attempt to rewrite if a single macro expansion creates multiple
+  // fields.
+  SourceLocation LastMacroLoc;
+  for (const auto &Field : Decl->fields()) {
+    if (!Field->getLocation().isMacroID())
+      continue;
+    SourceLocation MacroLoc =
+        Context.getSourceManager().getExpansionLoc(Field->getLocation());
+    if (LastMacroLoc.isValid() && MacroLoc == LastMacroLoc)
+      return false;
+    LastMacroLoc = MacroLoc;
+  }
+
+  // Prevent rewriting if there are preprocessor directives present between the
+  // start of the first field and the end of last field.
+  const SourceManager &SM = Context.getSourceManager();
+  std::pair<FileID, unsigned> FileAndOffset =
+      SM.getDecomposedLoc(Decl->field_begin()->getBeginLoc());
+  auto LastField = Decl->field_begin();
+  while (std::next(LastField) != Decl->field_end())
----------------
alexander-shaposhnikov wrote:

why not std::prev(Decl->field_end()) ?

https://github.com/llvm/llvm-project/pull/142149