[clang-tidy] Harden PreferMemberInitializerCheck

Prevent warning when the values are initialized using fields that will be initialized later or VarDecls defined in the constructors body.
Both of these cases can't be safely fixed.
Also improve logic of finding where to insert member initializers, previously it could be confused by in class member initializers.

Reviewed By: aaron.ballman

Differential Revision: https://reviews.llvm.org/D97132

diff --git a/clang-tools-extra/clang-tidy/cppcoreguidelines/PreferMemberInitializerCheck.cpp b/clang-tools-extra/clang-tidy/cppcoreguidelines/PreferMemberInitializerCheck.cpp
index 55d3576..6f056e7 100644 (file)
--- a/clang-tools-extra/clang-tidy/cppcoreguidelines/PreferMemberInitializerCheck.cpp
+++ b/clang-tools-extra/clang-tidy/cppcoreguidelines/PreferMemberInitializerCheck.cpp
@@ -55,8 +55,37 @@ static bool shouldBeDefaultMemberInitializer(const Expr *Value) {
   return false;
 }
 
+namespace {
+AST_MATCHER_P(FieldDecl, indexNotLessThan, unsigned, Index) {
+  return Node.getFieldIndex() >= Index;
+}
+} // namespace
+
+// Checks if Field is initialised using a field that will be initialised after
+// it.
+// TODO: Probably should guard against function calls that could have side
+// effects or if they do reference another field that's initialized before this
+// field, but is modified before the assignment.
+static bool isSafeAssignment(const FieldDecl *Field, const Expr *Init,
+                             const CXXConstructorDecl *Context) {
+
+  auto MemberMatcher =
+      memberExpr(hasObjectExpression(cxxThisExpr()),
+                 member(fieldDecl(indexNotLessThan(Field->getFieldIndex()))));
+
+  auto DeclMatcher = declRefExpr(
+      to(varDecl(unless(parmVarDecl()), hasDeclContext(equalsNode(Context)))));
+
+  return match(expr(anyOf(MemberMatcher, DeclMatcher,
+                          hasDescendant(MemberMatcher),
+                          hasDescendant(DeclMatcher))),
+               *Init, Field->getASTContext())
+      .empty();
+}
+
 static const std::pair<const FieldDecl *, const Expr *>
-isAssignmentToMemberOf(const RecordDecl *Rec, const Stmt *S) {
+isAssignmentToMemberOf(const CXXRecordDecl *Rec, const Stmt *S,
+                       const CXXConstructorDecl *Ctor) {
   if (const auto *BO = dyn_cast<BinaryOperator>(S)) {
     if (BO->getOpcode() != BO_Assign)
       return std::make_pair(nullptr, nullptr);
@@ -69,8 +98,11 @@ isAssignmentToMemberOf(const RecordDecl *Rec, const Stmt *S) {
     if (!Field)
       return std::make_pair(nullptr, nullptr);
 
-    if (isa<CXXThisExpr>(ME->getBase()))
-      return std::make_pair(Field, BO->getRHS()->IgnoreParenImpCasts());
+    if (!isa<CXXThisExpr>(ME->getBase()))
+      return std::make_pair(nullptr, nullptr);
+    const Expr *Init = BO->getRHS()->IgnoreParenImpCasts();
+    if (isSafeAssignment(Field, Init, Ctor))
+      return std::make_pair(Field, Init);
   } else if (const auto *COCE = dyn_cast<CXXOperatorCallExpr>(S)) {
     if (COCE->getOperator() != OO_Equal)
       return std::make_pair(nullptr, nullptr);
@@ -84,8 +116,11 @@ isAssignmentToMemberOf(const RecordDecl *Rec, const Stmt *S) {
     if (!Field)
       return std::make_pair(nullptr, nullptr);
 
-    if (isa<CXXThisExpr>(ME->getBase()))
-      return std::make_pair(Field, COCE->getArg(1)->IgnoreParenImpCasts());
+    if (!isa<CXXThisExpr>(ME->getBase()))
+      return std::make_pair(nullptr, nullptr);
+    const Expr *Init = COCE->getArg(1)->IgnoreParenImpCasts();
+    if (isSafeAssignment(Field, Init, Ctor))
+      return std::make_pair(Field, Init);
   }
 
   return std::make_pair(nullptr, nullptr);
@@ -118,14 +153,12 @@ void PreferMemberInitializerCheck::check(
   const auto *Body = cast<CompoundStmt>(Ctor->getBody());
 
   const CXXRecordDecl *Class = Ctor->getParent();
-  SourceLocation InsertPos;
   bool FirstToCtorInits = true;
 
   for (const Stmt *S : Body->body()) {
     if (S->getBeginLoc().isMacroID()) {
-      StringRef MacroName =
-        Lexer::getImmediateMacroName(S->getBeginLoc(), *Result.SourceManager,
-                                     getLangOpts());
+      StringRef MacroName = Lexer::getImmediateMacroName(
+          S->getBeginLoc(), *Result.SourceManager, getLangOpts());
       if (MacroName.contains_lower("assert"))
         return;
     }
@@ -143,97 +176,116 @@ void PreferMemberInitializerCheck::check(
 
     const FieldDecl *Field;
     const Expr *InitValue;
-    std::tie(Field, InitValue) = isAssignmentToMemberOf(Class, S);
+    std::tie(Field, InitValue) = isAssignmentToMemberOf(Class, S, Ctor);
     if (Field) {
       if (IsUseDefaultMemberInitEnabled && getLangOpts().CPlusPlus11 &&
           Ctor->isDefaultConstructor() &&
           (getLangOpts().CPlusPlus20 || !Field->isBitField()) &&
+          !Field->hasInClassInitializer() &&
           (!isa<RecordDecl>(Class->getDeclContext()) ||
            !cast<RecordDecl>(Class->getDeclContext())->isUnion()) &&
           shouldBeDefaultMemberInitializer(InitValue)) {
 
+        bool InvalidFix = false;
         SourceLocation FieldEnd =
             Lexer::getLocForEndOfToken(Field->getSourceRange().getEnd(), 0,
                                        *Result.SourceManager, getLangOpts());
-        SmallString<128> Insertion(
-            {UseAssignment ? " = " : "{",
-             Lexer::getSourceText(
-                 CharSourceRange(InitValue->getSourceRange(), true),
-                 *Result.SourceManager, getLangOpts()),
-             UseAssignment ? "" : "}"});
-
-        SourceLocation SemiColonEnd =
-            Lexer::findNextToken(S->getEndLoc(), *Result.SourceManager,
-                                 getLangOpts())
-                ->getEndLoc();
-        CharSourceRange StmtRange =
-            CharSourceRange::getCharRange(S->getBeginLoc(), SemiColonEnd);
-
-        diag(S->getBeginLoc(), "%0 should be initialized in an in-class"
-                               " default member initializer")
-            << Field << FixItHint::CreateInsertion(FieldEnd, Insertion)
-            << FixItHint::CreateRemoval(StmtRange);
+        InvalidFix |= FieldEnd.isInvalid() || FieldEnd.isMacroID();
+        SourceLocation SemiColonEnd;
+        if (auto NextToken = Lexer::findNextToken(
+                S->getEndLoc(), *Result.SourceManager, getLangOpts()))
+          SemiColonEnd = NextToken->getEndLoc();
+        else
+          InvalidFix = true;
+        auto Diag =
+            diag(S->getBeginLoc(), "%0 should be initialized in an in-class"
+                                   " default member initializer")
+            << Field;
+        if (!InvalidFix) {
+          CharSourceRange StmtRange =
+              CharSourceRange::getCharRange(S->getBeginLoc(), SemiColonEnd);
+
+          SmallString<128> Insertion(
+              {UseAssignment ? " = " : "{",
+               Lexer::getSourceText(
+                   CharSourceRange(InitValue->getSourceRange(), true),
+                   *Result.SourceManager, getLangOpts()),
+               UseAssignment ? "" : "}"});
+
+          Diag << FixItHint::CreateInsertion(FieldEnd, Insertion)
+               << FixItHint::CreateRemoval(StmtRange);
+        }
       } else {
-        SmallString<128> Insertion;
+        StringRef InsertPrefix = "";
+        SourceLocation InsertPos;
         bool AddComma = false;
-        if (!Ctor->getNumCtorInitializers() && FirstToCtorInits) {
-          SourceLocation BodyPos = Ctor->getBody()->getBeginLoc();
-          SourceLocation NextPos = Ctor->getBeginLoc();
-          do {
-            InsertPos = NextPos;
-            NextPos = Lexer::findNextToken(NextPos, *Result.SourceManager,
-                                           getLangOpts())
-                          ->getLocation();
-          } while (NextPos != BodyPos);
-          InsertPos = Lexer::getLocForEndOfToken(
-              InsertPos, 0, *Result.SourceManager, getLangOpts());
-
-          Insertion = " : ";
-        } else {
-          bool Found = false;
-          unsigned Index = Field->getFieldIndex();
-          for (const auto *Init : Ctor->inits()) {
-            if (Init->isMemberInitializer()) {
-              if (Index < Init->getMember()->getFieldIndex()) {
-                InsertPos = Init->getSourceLocation();
-                Found = true;
-                break;
-              }
-            }
+        bool InvalidFix = false;
+        unsigned Index = Field->getFieldIndex();
+        const CXXCtorInitializer *LastInListInit = nullptr;
+        for (const CXXCtorInitializer *Init : Ctor->inits()) {
+          if (!Init->isWritten())
+            continue;
+          if (Init->isMemberInitializer() &&
+              Index < Init->getMember()->getFieldIndex()) {
+            InsertPos = Init->getSourceLocation();
+            // There are initializers after the one we are inserting, so add a
+            // comma after this insertion in order to not break anything.
+            AddComma = true;
+            break;
           }
-
-          if (!Found) {
-            if (Ctor->getNumCtorInitializers()) {
-              InsertPos = Lexer::getLocForEndOfToken(
-                  (*Ctor->init_rbegin())->getSourceRange().getEnd(), 0,
-                  *Result.SourceManager, getLangOpts());
-            }
-            Insertion = ", ";
+          LastInListInit = Init;
+        }
+        if (InsertPos.isInvalid()) {
+          if (LastInListInit) {
+            InsertPos = Lexer::getLocForEndOfToken(
+                LastInListInit->getRParenLoc(), 0, *Result.SourceManager,
+                getLangOpts());
+            // Inserting after the last constructor initializer, so we need a
+            // comma.
+            InsertPrefix = ", ";
           } else {
-            AddComma = true;
+            InsertPos = Lexer::getLocForEndOfToken(
+                Ctor->getTypeSourceInfo()
+                    ->getTypeLoc()
+                    .getAs<clang::FunctionTypeLoc>()
+                    .getLocalRangeEnd(),
+                0, *Result.SourceManager, getLangOpts());
+
+            // If this is first time in the loop, there are no initializers so
+            // `:` declares member initialization list. If this is a subsequent
+            // pass then we have already inserted a `:` so continue with a
+            // comma.
+            InsertPrefix = FirstToCtorInits ? " : " : ", ";
           }
         }
-        Insertion.append(
-            {Field->getName(), "(",
-             Lexer::getSourceText(
-                 CharSourceRange(InitValue->getSourceRange(), true),
-                 *Result.SourceManager, getLangOpts()),
-             AddComma ? "), " : ")"});
-
-        SourceLocation SemiColonEnd =
-            Lexer::findNextToken(S->getEndLoc(), *Result.SourceManager,
-                                 getLangOpts())
-                ->getEndLoc();
-        CharSourceRange StmtRange =
-            CharSourceRange::getCharRange(S->getBeginLoc(), SemiColonEnd);
-
-        diag(S->getBeginLoc(), "%0 should be initialized in a member"
-                               " initializer of the constructor")
-            << Field
-            << FixItHint::CreateInsertion(InsertPos, Insertion,
-                                          FirstToCtorInits)
-            << FixItHint::CreateRemoval(StmtRange);
-        FirstToCtorInits = false;
+        InvalidFix |= InsertPos.isMacroID();
+
+        SourceLocation SemiColonEnd;
+        if (auto NextToken = Lexer::findNextToken(
+                S->getEndLoc(), *Result.SourceManager, getLangOpts()))
+          SemiColonEnd = NextToken->getEndLoc();
+        else
+          InvalidFix = true;
+
+        auto Diag =
+            diag(S->getBeginLoc(), "%0 should be initialized in a member"
+                                   " initializer of the constructor")
+            << Field;
+        if (!InvalidFix) {
+
+          CharSourceRange StmtRange =
+              CharSourceRange::getCharRange(S->getBeginLoc(), SemiColonEnd);
+          SmallString<128> Insertion(
+              {InsertPrefix, Field->getName(), "(",
+               Lexer::getSourceText(
+                   CharSourceRange(InitValue->getSourceRange(), true),
+                   *Result.SourceManager, getLangOpts()),
+               AddComma ? "), " : ")"});
+          Diag << FixItHint::CreateInsertion(InsertPos, Insertion,
+                                             FirstToCtorInits)
+               << FixItHint::CreateRemoval(StmtRange);
+          FirstToCtorInits = false;
+        }
       }
     }
   }

diff --git a/clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines-prefer-member-initializer.cpp b/clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines-prefer-member-initializer.cpp
index b5c04c3..73eeb21 100644 (file)
--- a/clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines-prefer-member-initializer.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines-prefer-member-initializer.cpp
@@ -488,3 +488,60 @@ Outside::Outside() {
     // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: 'x' should be initialized in a member initializer of the constructor [cppcoreguidelines-prefer-member-initializer]
     // CHECK-FIXES: {{^\ *$}}
 }
+
+struct SafeDependancy {
+  int m;
+  int n;
+  SafeDependancy(int M) : m(M) {
+    // CHECK-FIXES: SafeDependancy(int M) : m(M), n(m) {
+    n = m;
+    // CHECK-MESSAGES: :[[@LINE-1]]:5: warning: 'n' should be initialized in a member initializer of the constructor
+  }
+  // We match against direct field dependancy as well as descendant field
+  // dependancy, ensure both are accounted for.
+  SafeDependancy(short M) : m(M) {
+    // CHECK-FIXES: SafeDependancy(short M) : m(M), n(m + 1) {
+    n = m + 1;
+    // CHECK-MESSAGES: :[[@LINE-1]]:5: warning: 'n' should be initialized in a member initializer of the constructor
+  }
+};
+
+struct BadDependancy {
+  int m;
+  int n;
+  BadDependancy(int N) : n(N) {
+    m = n;
+  }
+  BadDependancy(short N) : n(N) {
+    m = n + 1;
+  }
+};
+
+struct InitFromVarDecl {
+  int m;
+  InitFromVarDecl() {
+    // Can't apply this fix as n is declared in the body of the constructor.
+    int n = 3;
+    m = n;
+  }
+};
+
+struct AlreadyHasInit {
+  int m = 4;
+  AlreadyHasInit() {
+    m = 3;
+    // CHECK-MESSAGES: :[[@LINE-1]]:5: warning: 'm' should be initialized in a member initializer of the constructor
+  }
+};
+
+#define ASSIGN_IN_MACRO(FIELD, VALUE) FIELD = (VALUE);
+
+struct MacroCantFix {
+  int n; // NoFix
+  // CHECK-FIXES: int n; // NoFix
+  MacroCantFix() {
+    ASSIGN_IN_MACRO(n, 0)
+    // CHECK-MESSAGES: :[[@LINE-1]]:21: warning: 'n' should be initialized in a member initializer of the constructor
+    // CHECK-FIXES: ASSIGN_IN_MACRO(n, 0)
+  }
+};