[clang-tidy] new cppcoreguidelines-narrowing-conversions check.

Summary:
Checks for narrowing conversions, e.g.

int i = 0;
i += 0.1;

This has what some might consider false positives for:
i += ceil(d);

Reviewers: alexfh, hokein

Subscribers: srhines, nemanjai, mgorny, JDevlieghere, xazax.hun, kbarton

Differential Revision: https://reviews.llvm.org/D38455

llvm-svn: 333066

4 files changed, 111 insertions, 0 deletions

diff --git a/clang-tools-extra/clang-tidy/cppcoreguidelines/CMakeLists.txt b/clang-tools-extra/clang-tidy/cppcoreguidelines/CMakeLists.txt
index 2ce1a0800de..49fedd62203 100644
--- a/clang-tools-extra/clang-tidy/cppcoreguidelines/CMakeLists.txt
+++ b/clang-tools-extra/clang-tidy/cppcoreguidelines/CMakeLists.txt
@@ -4,6 +4,7 @@ add_clang_library(clangTidyCppCoreGuidelinesModule
   AvoidGotoCheck.cpp
   CppCoreGuidelinesTidyModule.cpp
   InterfacesGlobalInitCheck.cpp
+  NarrowingConversionsCheck.cpp
   NoMallocCheck.cpp
   OwningMemoryCheck.cpp
   ProBoundsArrayToPointerDecayCheck.cpp
diff --git a/clang-tools-extra/clang-tidy/cppcoreguidelines/CppCoreGuidelinesTidyModule.cpp b/clang-tools-extra/clang-tidy/cppcoreguidelines/CppCoreGuidelinesTidyModule.cpp
index 51824eca9ac..a0392594696 100644
--- a/clang-tools-extra/clang-tidy/cppcoreguidelines/CppCoreGuidelinesTidyModule.cpp
+++ b/clang-tools-extra/clang-tidy/cppcoreguidelines/CppCoreGuidelinesTidyModule.cpp
@@ -13,6 +13,7 @@
 #include "../misc/UnconventionalAssignOperatorCheck.h"
 #include "AvoidGotoCheck.h"
 #include "InterfacesGlobalInitCheck.h"
+#include "NarrowingConversionsCheck.h"
 #include "NoMallocCheck.h"
 #include "OwningMemoryCheck.h"
 #include "ProBoundsArrayToPointerDecayCheck.h"
@@ -40,6 +41,8 @@ public:
         "cppcoreguidelines-avoid-goto");
     CheckFactories.registerCheck<InterfacesGlobalInitCheck>(
         "cppcoreguidelines-interfaces-global-init");
+    CheckFactories.registerCheck<NarrowingConversionsCheck>(
+        "cppcoreguidelines-narrowing-conversions");
     CheckFactories.registerCheck<NoMallocCheck>("cppcoreguidelines-no-malloc");
     CheckFactories.registerCheck<OwningMemoryCheck>(
         "cppcoreguidelines-owning-memory");
diff --git a/clang-tools-extra/clang-tidy/cppcoreguidelines/NarrowingConversionsCheck.cpp b/clang-tools-extra/clang-tidy/cppcoreguidelines/NarrowingConversionsCheck.cpp
new file mode 100644
index 00000000000..2c5676e76a2
--- /dev/null
+++ b/clang-tools-extra/clang-tidy/cppcoreguidelines/NarrowingConversionsCheck.cpp
@@ -0,0 +1,70 @@
+//===--- NarrowingConversionsCheck.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 "NarrowingConversionsCheck.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang {
+namespace tidy {
+namespace cppcoreguidelines {
+
+// FIXME: Check double -> float truncation. Pay attention to casts:
+void NarrowingConversionsCheck::registerMatchers(MatchFinder *Finder) {
+  // ceil() and floor() are guaranteed to return integers, even though the type
+  // is not integral.
+  const auto IsCeilFloorCall = callExpr(callee(functionDecl(
+      hasAnyName("::ceil", "::std::ceil", "::floor", "::std::floor"))));
+
+  const auto IsFloatExpr =
+      expr(hasType(realFloatingPointType()), unless(IsCeilFloorCall));
+
+  // casts:
+  //   i = 0.5;
+  //   void f(int); f(0.5);
+  Finder->addMatcher(implicitCastExpr(hasImplicitDestinationType(isInteger()),
+                                      hasSourceExpression(IsFloatExpr),
+                                      unless(hasParent(castExpr())),
+                                      unless(isInTemplateInstantiation()))
+                         .bind("cast"),
+                     this);
+
+  // Binary operators:
+  //   i += 0.5;
+  Finder->addMatcher(
+      binaryOperator(isAssignmentOperator(),
+                     // The `=` case generates an implicit cast which is covered
+                     // by the previous matcher.
+                     unless(hasOperatorName("=")),
+                     hasLHS(hasType(isInteger())), hasRHS(IsFloatExpr),
+                     unless(isInTemplateInstantiation()))
+          .bind("op"),
+      this);
+}
+
+void NarrowingConversionsCheck::check(const MatchFinder::MatchResult &Result) {
+  if (const auto *Op = Result.Nodes.getNodeAs<BinaryOperator>("op")) {
+    if (Op->getLocStart().isMacroID())
+      return;
+    diag(Op->getOperatorLoc(), "narrowing conversion from %0 to %1")
+        << Op->getRHS()->getType() << Op->getLHS()->getType();
+    return;
+  }
+  const auto *Cast = Result.Nodes.getNodeAs<ImplicitCastExpr>("cast");
+  if (Cast->getLocStart().isMacroID())
+    return;
+  diag(Cast->getExprLoc(), "narrowing conversion from %0 to %1")
+      << Cast->getSubExpr()->getType() << Cast->getType();
+}
+
+} // namespace cppcoreguidelines
+} // namespace tidy
+} // namespace clang
diff --git a/clang-tools-extra/clang-tidy/cppcoreguidelines/NarrowingConversionsCheck.h b/clang-tools-extra/clang-tidy/cppcoreguidelines/NarrowingConversionsCheck.h
new file mode 100644
index 00000000000..35f58bc220a
--- /dev/null
+++ b/clang-tools-extra/clang-tidy/cppcoreguidelines/NarrowingConversionsCheck.h
@@ -0,0 +1,37 @@
+//===--- NarrowingConversionsCheck.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_CPPCOREGUIDELINES_NARROWING_CONVERSIONS_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_CPPCOREGUIDELINES_NARROWING_CONVERSIONS_H
+
+#include "../ClangTidy.h"
+
+namespace clang {
+namespace tidy {
+namespace cppcoreguidelines {
+
+/// Checks for narrowing conversions, e.g:
+///   int i = 0;
+///   i += 0.1;
+///
+/// For the user-facing documentation see:
+/// http://clang.llvm.org/extra/clang-tidy/checks/cppcoreguidelines-narrowing-conversions.html
+class NarrowingConversionsCheck : public ClangTidyCheck {
+public:
+  NarrowingConversionsCheck(StringRef Name, ClangTidyContext *Context)
+      : ClangTidyCheck(Name, Context) {}
+  void registerMatchers(ast_matchers::MatchFinder *Finder) override;
+  void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+};
+
+} // namespace cppcoreguidelines
+} // namespace tidy
+} // namespace clang
+
+#endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_CPPCOREGUIDELINES_NARROWING_CONVERSIONS_H