DanglingHandleCheck.cpp

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//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
 
#include "DanglingHandleCheck.h"
#include "../utils/OptionsUtils.h"
#include "clang/AST/ASTContext.h"
#include "clang/ASTMatchers/ASTMatchFinder.h"
 
using namespace clang::ast_matchers;
 
namespace clang::tidy::bugprone {
 
static ast_matchers::internal::BindableMatcher<Stmt>
handleFrom(const ast_matchers::internal::Matcher<RecordDecl> &IsAHandle,
           const ast_matchers::internal::Matcher<Expr> &Arg) {
  return expr(
      anyOf(cxxConstructExpr(hasDeclaration(cxxMethodDecl(ofClass(IsAHandle))),
                             hasArgument(0, Arg)),
            cxxMemberCallExpr(hasType(hasUnqualifiedDesugaredType(recordType(
                                  hasDeclaration(cxxRecordDecl(IsAHandle))))),
                              callee(memberExpr(member(cxxConversionDecl()))),
                              on(Arg))));
}
 
static ast_matchers::internal::Matcher<Stmt> handleFromTemporaryValue(
    const ast_matchers::internal::Matcher<RecordDecl> &IsAHandle) {
  const auto TemporaryExpr = anyOf(
      cxxBindTemporaryExpr(),
      cxxFunctionalCastExpr(
          hasCastKind(CK_ConstructorConversion),
          hasSourceExpression(ignoringParenImpCasts(cxxBindTemporaryExpr()))));
  // If a ternary operator returns a temporary value, then both branches hold a
  // temporary value. If one of them is not a temporary then it must be copied
  // into one to satisfy the type of the operator.
  const auto TemporaryTernary = conditionalOperator(
      hasTrueExpression(ignoringParenImpCasts(TemporaryExpr)),
      hasFalseExpression(ignoringParenImpCasts(TemporaryExpr)));
 
  return handleFrom(IsAHandle, anyOf(TemporaryExpr, TemporaryTernary));
}
 
static ast_matchers::internal::Matcher<RecordDecl> isASequence() {
  return hasAnyName("::std::deque", "::std::forward_list", "::std::list",
                    "::std::vector");
}
 
static ast_matchers::internal::Matcher<RecordDecl> isASet() {
  return hasAnyName("::std::set", "::std::multiset", "::std::unordered_set",
                    "::std::unordered_multiset");
}
 
static ast_matchers::internal::Matcher<RecordDecl> isAMap() {
  return hasAnyName("::std::map", "::std::multimap", "::std::unordered_map",
                    "::std::unordered_multimap");
}
 
static ast_matchers::internal::BindableMatcher<Stmt> makeContainerMatcher(
    const ast_matchers::internal::Matcher<RecordDecl> &IsAHandle) {
  // This matcher could be expanded to detect:
  //  - Constructors: eg. vector<string_view>(3, string("A"));
  //  - emplace*(): This requires a different logic to determine that
  //                the conversion will happen inside the container.
  //  - map's insert: This requires detecting that the pair conversion triggers
  //                  the bug. A little more complicated than what we have now.
  return callExpr(
      hasAnyArgument(
          ignoringParenImpCasts(handleFromTemporaryValue(IsAHandle))),
      anyOf(
          // For sequences: assign, push_back, resize.
          cxxMemberCallExpr(
              callee(functionDecl(hasAnyName("assign", "push_back", "resize"))),
              on(expr(hasType(hasUnqualifiedDesugaredType(
                  recordType(hasDeclaration(recordDecl(isASequence())))))))),
          // For sequences and sets: insert.
          cxxMemberCallExpr(callee(functionDecl(hasName("insert"))),
                            on(expr(hasType(hasUnqualifiedDesugaredType(
                                recordType(hasDeclaration(recordDecl(
                                    anyOf(isASequence(), isASet()))))))))),
          // For maps: operator[].
          cxxOperatorCallExpr(callee(cxxMethodDecl(ofClass(isAMap()))),
                              hasOverloadedOperatorName("[]"))));
}
 
DanglingHandleCheck::DanglingHandleCheck(StringRef Name,
                                         ClangTidyContext *Context)
    : ClangTidyCheck(Name, Context),
      HandleClasses(utils::options::parseStringList(Options.get(
          "HandleClasses", "std::basic_string_view;std::experimental::basic_"
                           "string_view;std::span"))),
      IsAHandle(cxxRecordDecl(hasAnyName(HandleClasses)).bind("handle")) {}
 
void DanglingHandleCheck::storeOptions(ClangTidyOptions::OptionMap &Opts) {
  Options.store(Opts, "HandleClasses",
                utils::options::serializeStringList(HandleClasses));
}
 
void DanglingHandleCheck::registerMatchersForVariables(MatchFinder *Finder) {
  const auto ConvertedHandle = handleFromTemporaryValue(IsAHandle);
 
  // Find 'Handle foo(ReturnsAValue());', 'Handle foo = ReturnsAValue();'
  Finder->addMatcher(
      varDecl(hasType(hasUnqualifiedDesugaredType(
                  recordType(hasDeclaration(cxxRecordDecl(IsAHandle))))),
              unless(parmVarDecl()),
              hasInitializer(
                  exprWithCleanups(ignoringElidableConstructorCall(has(
                                       ignoringParenImpCasts(ConvertedHandle))))
                      .bind("bad_stmt"))),
      this);
 
  // Find 'foo = ReturnsAValue();  // foo is Handle'
  Finder->addMatcher(
      traverse(TK_AsIs,
               cxxOperatorCallExpr(callee(cxxMethodDecl(ofClass(IsAHandle))),
                                   hasOverloadedOperatorName("="),
                                   hasArgument(1, ConvertedHandle))
                   .bind("bad_stmt")),
      this);
 
  // Container insertions that will dangle.
  Finder->addMatcher(
      traverse(TK_AsIs, makeContainerMatcher(IsAHandle).bind("bad_stmt")),
      this);
}
 
void DanglingHandleCheck::registerMatchersForReturn(MatchFinder *Finder) {
  // Return a local.
  Finder->addMatcher(
      traverse(TK_AsIs,
               returnStmt(
                   // The AST contains two constructor calls:
                   //   1. Value to Handle conversion.
                   //   2. Handle copy construction (elided in C++17+).
                   // We have to match both.
                   has(ignoringImplicit(ignoringElidableConstructorCall(
                       ignoringImplicit(handleFrom(
                           IsAHandle,
                           declRefExpr(to(varDecl(
                               // Is function scope ...
                               hasAutomaticStorageDuration(),
                               // ... and it is a local array or Value.
                               anyOf(hasType(arrayType()),
                                     hasType(hasUnqualifiedDesugaredType(
                                         recordType(hasDeclaration(recordDecl(
                                             unless(IsAHandle))))))))))))))),
                   // Temporary fix for false positives inside lambdas.
                   unless(hasAncestor(lambdaExpr())))
                   .bind("bad_stmt")),
      this);
 
  // Return a temporary.
  Finder->addMatcher(
      traverse(TK_AsIs,
               returnStmt(has(exprWithCleanups(ignoringElidableConstructorCall(
                              has(ignoringParenImpCasts(
                                  handleFromTemporaryValue(IsAHandle)))))))
                   .bind("bad_stmt")),
      this);
}
 
void DanglingHandleCheck::registerMatchers(MatchFinder *Finder) {
  registerMatchersForVariables(Finder);
  registerMatchersForReturn(Finder);
}
 
void DanglingHandleCheck::check(const MatchFinder::MatchResult &Result) {
  auto *Handle = Result.Nodes.getNodeAs<CXXRecordDecl>("handle");
  diag(Result.Nodes.getNodeAs<Stmt>("bad_stmt")->getBeginLoc(),
       "%0 outlives its value")
      << Handle->getQualifiedNameAsString();
}
 
} // namespace clang::tidy::bugprone