JonasToth created this revision.
JonasToth added reviewers: rsmith, aaron.ballman, alexfh, hokein.
Herald added subscribers: cfe-commits, xazax.hun, mgorny.

The idea of this check is to enforce one decl per statement and to include
an automated code transformation for all multi-decl statments.
It turns out this is more complicated then I excepted, so this differential
is a playground for now to allow easy commenting and discussions on the code.


Repository:
  rCTE Clang Tools Extra

https://reviews.llvm.org/D51949

Files:
  clang-tidy/readability/CMakeLists.txt
  clang-tidy/readability/IsolateDeclCheck.cpp
  clang-tidy/readability/IsolateDeclCheck.h
  clang-tidy/readability/ReadabilityTidyModule.cpp
  docs/ReleaseNotes.rst
  docs/clang-tidy/checks/list.rst
  docs/clang-tidy/checks/readability-isolate-decl.rst
  test/clang-tidy/readability-isolate-decl.cpp

Index: test/clang-tidy/readability-isolate-decl.cpp
===================================================================
--- /dev/null
+++ test/clang-tidy/readability-isolate-decl.cpp
@@ -0,0 +1,65 @@
+// RUN: %check_clang_tidy %s readability-isolate-decl %t
+
+void f() {
+  int i;
+}
+
+void f2() {
+  int i, j, *k, lala = 42;
+  // CHECK-MESSAGES: [[@LINE-1]]:3: warning: make only one declaration per statement
+  // CHECK-FIXES: int i;int j;int * k;int lala = 42;
+  //
+  int normal, weird = /* comment */ 42;
+  // CHECK-MESSAGES: [[@LINE-1]]:3: warning: make only one declaration per statement
+  // CHECK-FIXES: int normal;int weird = 42;
+}
+
+void f3() {
+  int i, *pointer1;
+  // CHECK-MESSAGES: [[@LINE-1]]:3: warning: make only one declaration per statement
+  // CHECK-FIXES: int i;int * pointer1;
+  //
+  int *pointer2 = nullptr, *pointer3 = &i;
+  // CHECK-MESSAGES: [[@LINE-1]]:3: warning: make only one declaration per statement
+  // CHECK-FIXES: int * pointer2 = nullpt;int * pointer3 = &i;
+}
+
+void f4() {
+  // clang-format off
+  double d = 42./* foo */, z = 43., /* hi */ y, c /* */ /*  */, l = 2.;
+  // CHECK-MESSAGES: [[@LINE-1]]:3: warning: make only one declaration per statement
+  // CHECK-FIXES: double d = 42;double z = 43;double y;double c;double l = 2.;
+  // clang-format on
+}
+
+struct SomeClass {
+  SomeClass() = default;
+  SomeClass(int value);
+};
+void f5() {
+  SomeClass v1, v2(42), v3{42}, v4(42.5);
+  // CHECK-MESSAGES: [[@LINE-1]]:3: warning: make only one declaration per statement
+  // CHECK-FIXES: SomeClass v1 = v1;SomeClass v2 = v2(42);SomeClass v3 = v3{42};SomeClass v4 = v4(42.5);
+
+  SomeClass v5 = 42, *p1 = nullptr;
+  // CHECK-MESSAGES: [[@LINE-1]]:3: warning: make only one declaration per statement
+  // CHECK-FIXES: SomeClass v5 = v5 = 42;SomeClass * p1 = nullpt;
+}
+
+void f6() {
+  int array1[] = {1, 2, 3, 4}, array2[] = {1, 2, 3}, value1, value2 = 42;
+  // CHECK-MESSAGES: [[@LINE-1]]:3: warning: make only one declaration per statement
+  // CHECK-FIXES: int [4] array1 = {1, 2, 3, 4};int [3] array2 = {1, 2, 3};int value1;int value2 = 42;
+}
+
+template <typename T>
+struct TemplatedType {
+    TemplatedType() = default;
+    TemplatedType(T value);
+};
+
+void f7() {
+  TemplatedType<int> TT1(42), TT2{42}, TT3;
+  // CHECK-MESSAGES: [[@LINE-1]]:3: warning: make only one declaration per statement
+  // CHECK-FIXES: TemplatedType<int> TT1 = TT1(42);TemplatedType<int> TT2 = TT2{42};TemplatedType<int> TT3 = TT;
+}
Index: docs/clang-tidy/checks/readability-isolate-decl.rst
===================================================================
--- /dev/null
+++ docs/clang-tidy/checks/readability-isolate-decl.rst
@@ -0,0 +1,6 @@
+.. title:: clang-tidy - readability-isolate-decl
+
+readability-isolate-decl
+========================
+
+FIXME: Describe what patterns does the check detect and why. Give examples.
Index: docs/clang-tidy/checks/list.rst
===================================================================
--- docs/clang-tidy/checks/list.rst
+++ docs/clang-tidy/checks/list.rst
@@ -225,6 +225,7 @@
    readability-identifier-naming
    readability-implicit-bool-conversion
    readability-inconsistent-declaration-parameter-name
+   readability-isolate-decl
    readability-magic-numbers
    readability-misleading-indentation
    readability-misplaced-array-index
Index: docs/ReleaseNotes.rst
===================================================================
--- docs/ReleaseNotes.rst
+++ docs/ReleaseNotes.rst
@@ -93,6 +93,11 @@
   Flags uses of ``absl::StrCat()`` to append to a ``std::string``. Suggests 
   ``absl::StrAppend()`` should be used instead.
 
+- New :doc:`readability-isolate-decl
+  <clang-tidy/checks/readability-isolate-decl>` check.
+
+  FIXME: add release notes.
+
 - New :doc:`readability-magic-numbers
   <clang-tidy/checks/readability-magic-numbers>` check.
 
Index: clang-tidy/readability/ReadabilityTidyModule.cpp
===================================================================
--- clang-tidy/readability/ReadabilityTidyModule.cpp
+++ clang-tidy/readability/ReadabilityTidyModule.cpp
@@ -20,6 +20,7 @@
 #include "IdentifierNamingCheck.h"
 #include "ImplicitBoolConversionCheck.h"
 #include "InconsistentDeclarationParameterNameCheck.h"
+#include "IsolateDeclCheck.h"
 #include "MagicNumbersCheck.h"
 #include "MisleadingIndentationCheck.h"
 #include "MisplacedArrayIndexCheck.h"
@@ -66,6 +67,8 @@
         "readability-implicit-bool-conversion");
     CheckFactories.registerCheck<InconsistentDeclarationParameterNameCheck>(
         "readability-inconsistent-declaration-parameter-name");
+    CheckFactories.registerCheck<IsolateDeclCheck>(
+        "readability-isolate-decl");
     CheckFactories.registerCheck<MagicNumbersCheck>(
         "readability-magic-numbers");
     CheckFactories.registerCheck<MisleadingIndentationCheck>(
Index: clang-tidy/readability/IsolateDeclCheck.h
===================================================================
--- /dev/null
+++ clang-tidy/readability/IsolateDeclCheck.h
@@ -0,0 +1,35 @@
+//===--- IsolateDeclCheck.h - clang-tidy-------------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_READABILITY_ISOLATEDECLCHECK_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_READABILITY_ISOLATEDECLCHECK_H
+
+#include "../ClangTidy.h"
+
+namespace clang {
+namespace tidy {
+namespace readability {
+
+/// FIXME: Write a short description.
+///
+/// For the user-facing documentation see:
+/// http://clang.llvm.org/extra/clang-tidy/checks/readability-isolate-decl.html
+class IsolateDeclCheck : public ClangTidyCheck {
+public:
+  IsolateDeclCheck(StringRef Name, ClangTidyContext *Context)
+      : ClangTidyCheck(Name, Context) {}
+  void registerMatchers(ast_matchers::MatchFinder *Finder) override;
+  void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+};
+
+} // namespace readability
+} // namespace tidy
+} // namespace clang
+
+#endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_READABILITY_ISOLATEDECLCHECK_H
Index: clang-tidy/readability/IsolateDeclCheck.cpp
===================================================================
--- /dev/null
+++ clang-tidy/readability/IsolateDeclCheck.cpp
@@ -0,0 +1,79 @@
+//===--- IsolateDeclCheck.cpp - clang-tidy---------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "IsolateDeclCheck.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/Lex/Lexer.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang {
+namespace tidy {
+namespace readability {
+
+namespace {
+AST_MATCHER(DeclStmt, isSingleDecl) { return Node.isSingleDecl(); }
+} // namespace
+
+void IsolateDeclCheck::registerMatchers(MatchFinder *Finder) {
+  Finder->addMatcher(declStmt(unless(isSingleDecl())).bind("decl_stmt"), this);
+}
+
+namespace {
+std::string GetIsolatedDecl(const VarDecl *D, const SourceManager &SM,
+                            const LangOptions &LangOpts) {
+  QualType VarType = D->getType();
+  PrintingPolicy TypePrinter(LangOpts);
+
+  std::string TypeAndName =
+      VarType.getAsString(TypePrinter) + " " + D->getNameAsString();
+  std::string Initializer = "";
+
+  if (D->hasInit()) {
+    SourceRange InclusiveRange(D->getInit()->getBeginLoc(),
+                               D->getInit()->getEndLoc().getLocWithOffset(2));
+    assert(InclusiveRange.isValid() && "Invalid Source Range created");
+
+    CharSourceRange R = Lexer::getAsCharRange(InclusiveRange, SM, LangOpts);
+    assert(R.isValid() && "Retrieved invalid char source range");
+
+    bool InvalidText = false;
+    Initializer = Lexer::getSourceText(R, SM, LangOpts, &InvalidText).str();
+    assert(!InvalidText && "Retrieved invalid text");
+
+    return TypeAndName + " = " + Initializer + ";";
+  }
+
+  return TypeAndName + ";";
+}
+} // namespace
+
+void IsolateDeclCheck::check(const MatchFinder::MatchResult &Result) {
+  const auto *WholeDecl = Result.Nodes.getNodeAs<DeclStmt>("decl_stmt");
+  std::string Replacement = "";
+
+  for (const Decl *D : WholeDecl->decls()) {
+    const auto *VD = dyn_cast<VarDecl>(D);
+    if (VD == nullptr) {
+      Replacement.clear();
+      break;
+    }
+    Replacement += GetIsolatedDecl(VD, *Result.SourceManager, getLangOpts());
+  }
+  auto Diag =
+      diag(WholeDecl->getBeginLoc(), "make only one declaration per statement");
+
+  if (!Replacement.empty())
+    Diag << FixItHint::CreateReplacement(WholeDecl->getSourceRange(),
+                                         Replacement);
+}
+} // namespace readability
+} // namespace tidy
+} // namespace clang
Index: clang-tidy/readability/CMakeLists.txt
===================================================================
--- clang-tidy/readability/CMakeLists.txt
+++ clang-tidy/readability/CMakeLists.txt
@@ -11,6 +11,7 @@
   IdentifierNamingCheck.cpp
   ImplicitBoolConversionCheck.cpp
   InconsistentDeclarationParameterNameCheck.cpp
+  IsolateDeclCheck.cpp
   MagicNumbersCheck.cpp
   MisleadingIndentationCheck.cpp
   MisplacedArrayIndexCheck.cpp
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