loplugin:casttovoid

Change-Id: I427b15b35ef6e7c803cb8a00c961d35175ae8cb2

1 files changed, 494 insertions, 0 deletions

diff --git a/compilerplugins/clang/casttovoid.cxx b/compilerplugins/clang/casttovoid.cxx
new file mode 100644
index 000000000000..997f7ed83e7c
--- /dev/null
+++ b/compilerplugins/clang/casttovoid.cxx
@@ -0,0 +1,494 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4; fill-column: 100 -*- */
+/*
+ * This file is part of the LibreOffice project.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+#include <algorithm>
+#include <cassert>
+#include <map>
+#include <stack>
+
+#include "clang/AST/Attr.h"
+
+#include "check.hxx"
+#include "compat.hxx"
+#include "plugin.hxx"
+
+namespace {
+
+bool isWarnUnusedType(QualType type) {
+    if (auto const t = type->getAs<TypedefType>()) {
+        if (t->getDecl()->hasAttr<WarnUnusedAttr>()) {
+            return true;
+        }
+    }
+    if (auto const t = type->getAs<RecordType>()) {
+        if (t->getDecl()->hasAttr<WarnUnusedAttr>()) {
+            return true;
+        }
+    }
+    return loplugin::isExtraWarnUnusedType(type);
+}
+
+Expr const * lookThroughInitListExpr(Expr const * expr) {
+    if (auto const ile = dyn_cast<InitListExpr>(expr->IgnoreParenImpCasts())) {
+        if (ile->getNumInits() == 1) {
+            return ile->getInit(0);
+        }
+    }
+    return expr;
+}
+
+class Visitor final:
+    public RecursiveASTVisitor<Visitor>, public loplugin::Plugin
+{
+public:
+    explicit Visitor(InstantiationData const & data): Plugin(data) {}
+
+    bool TraverseCStyleCastExpr(CStyleCastExpr * expr) {
+        auto const dre = checkCast(expr);
+        if (dre != nullptr) {
+            castToVoid_.push({expr, dre});
+        }
+        auto const ret = RecursiveASTVisitor::TraverseCStyleCastExpr(expr);
+        if (dre != nullptr) {
+            assert(!castToVoid_.empty());
+            assert(castToVoid_.top().cast == expr);
+            assert(castToVoid_.top().sub == dre);
+            castToVoid_.pop();
+        }
+        return ret;
+    }
+
+    bool TraverseCXXStaticCastExpr(CXXStaticCastExpr * expr) {
+        auto const dre = checkCast(expr);
+        if (dre != nullptr) {
+            castToVoid_.push({expr, dre});
+        }
+        auto const ret = RecursiveASTVisitor::TraverseCXXStaticCastExpr(expr);
+        if (dre != nullptr) {
+            assert(!castToVoid_.empty());
+            assert(castToVoid_.top().cast == expr);
+            assert(castToVoid_.top().sub == dre);
+            castToVoid_.pop();
+        }
+        return ret;
+    }
+
+    bool TraverseCXXFunctionalCastExpr(CXXFunctionalCastExpr * expr) {
+        auto const dre = checkCast(expr);
+        if (dre != nullptr) {
+            castToVoid_.push({expr, dre});
+        }
+        auto const ret = RecursiveASTVisitor::TraverseCXXFunctionalCastExpr(
+            expr);
+        if (dre != nullptr) {
+            assert(!castToVoid_.empty());
+            assert(castToVoid_.top().cast == expr);
+            assert(castToVoid_.top().sub == dre);
+            castToVoid_.pop();
+        }
+        return ret;
+    }
+
+    bool TraverseFunctionDecl(FunctionDecl * decl) {
+        returnTypes_.push(decl->getReturnType());
+        auto const ret = RecursiveASTVisitor::TraverseFunctionDecl(decl);
+        assert(!returnTypes_.empty());
+        assert(returnTypes_.top() == decl->getReturnType());
+        returnTypes_.pop();
+        return ret;
+    }
+
+#if CLANG_VERSION >= 50000
+    bool TraverseCXXDeductionGuideDecl(CXXDeductionGuideDecl * decl) {
+        returnTypes_.push(decl->getReturnType());
+        auto const ret = RecursiveASTVisitor::TraverseCXXDeductionGuideDecl(
+            decl);
+        assert(!returnTypes_.empty());
+        assert(returnTypes_.top() == decl->getReturnType());
+        returnTypes_.pop();
+        return ret;
+    }
+#endif
+
+    bool TraverseCXXMethodDecl(CXXMethodDecl * decl) {
+        returnTypes_.push(decl->getReturnType());
+        auto const ret = RecursiveASTVisitor::TraverseCXXMethodDecl(decl);
+        assert(!returnTypes_.empty());
+        assert(returnTypes_.top() == decl->getReturnType());
+        returnTypes_.pop();
+        return ret;
+    }
+
+    bool TraverseCXXConstructorDecl(CXXConstructorDecl * decl) {
+        returnTypes_.push(decl->getReturnType());
+        auto const ret = RecursiveASTVisitor::TraverseCXXConstructorDecl(decl);
+        assert(!returnTypes_.empty());
+        assert(returnTypes_.top() == decl->getReturnType());
+        returnTypes_.pop();
+        return ret;
+    }
+
+    bool TraverseCXXDestructorDecl(CXXDestructorDecl * decl) {
+        returnTypes_.push(decl->getReturnType());
+        auto const ret = RecursiveASTVisitor::TraverseCXXDestructorDecl(decl);
+        assert(!returnTypes_.empty());
+        assert(returnTypes_.top() == decl->getReturnType());
+        returnTypes_.pop();
+        return ret;
+    }
+
+    bool TraverseCXXConversionDecl(CXXConversionDecl * decl) {
+        returnTypes_.push(decl->getReturnType());
+        auto const ret = RecursiveASTVisitor::TraverseCXXConversionDecl(decl);
+        assert(!returnTypes_.empty());
+        assert(returnTypes_.top() == decl->getReturnType());
+        returnTypes_.pop();
+        return ret;
+    }
+
+    bool TraverseConstructorInitializer(CXXCtorInitializer * init) {
+        if (auto const field = init->getAnyMember()) {
+            if (loplugin::TypeCheck(field->getType()).LvalueReference()) {
+                recordConsumption(lookThroughInitListExpr(init->getInit()));
+            }
+        }
+        return RecursiveASTVisitor::TraverseConstructorInitializer(init);
+    }
+
+    bool VisitDeclRefExpr(DeclRefExpr const * expr) {
+        if (ignoreLocation(expr)) {
+            return true;
+        }
+        auto const var = dyn_cast<VarDecl>(expr->getDecl());
+        if (var == nullptr) {
+            return true;
+        }
+        auto & usage = vars_[var->getCanonicalDecl()];
+        if (!castToVoid_.empty() && castToVoid_.top().sub == expr) {
+            usage.castToVoid.push_back(castToVoid_.top().cast);
+        } else {
+            usage.mentioned = true;
+        }
+        return true;
+    }
+
+    bool VisitImplicitCastExpr(ImplicitCastExpr const * expr) {
+        if (ignoreLocation(expr)) {
+            return true;
+        }
+        if (expr->getCastKind() != CK_LValueToRValue) {
+            return true;
+        }
+        recordConsumption(expr->getSubExpr());
+        return true;
+    }
+
+    bool VisitCallExpr(CallExpr const * expr) {
+        if (ignoreLocation(expr)) {
+            return true;
+        }
+        unsigned firstArg = 0;
+        if (auto const cmce = dyn_cast<CXXMemberCallExpr>(expr)) {
+            recordConsumption(cmce->getImplicitObjectArgument());
+        } else if (isa<CXXOperatorCallExpr>(expr)) {
+            auto const dc = expr->getDirectCallee();
+            if (dc != nullptr && isa<CXXMethodDecl>(dc)) {
+                assert(expr->getNumArgs() != 0);
+                recordConsumption(expr->getArg(0));
+                firstArg = 1;
+            }
+        }
+        auto fun = expr->getDirectCallee();
+        if (fun == nullptr) {
+            return true;
+        }
+        unsigned const n = std::min(fun->getNumParams(), expr->getNumArgs());
+        for (unsigned i = firstArg; i < n; ++i) {
+            if (!loplugin::TypeCheck(fun->getParamDecl(i)->getType())
+                .LvalueReference().Const())
+            {
+                continue;
+            }
+            recordConsumption(lookThroughInitListExpr(expr->getArg(i)));
+        }
+        return true;
+    }
+
+    bool VisitCXXConstructExpr(CXXConstructExpr const * expr) {
+        if (ignoreLocation(expr)) {
+            return true;
+        }
+        auto const ctor = expr->getConstructor();
+        unsigned const n = std::min(ctor->getNumParams(), expr->getNumArgs());
+        for (unsigned i = 0; i != n; ++i) {
+            if (!loplugin::TypeCheck(ctor->getParamDecl(i)->getType())
+                .LvalueReference().Const())
+            {
+                continue;
+            }
+            recordConsumption(lookThroughInitListExpr(expr->getArg(i)));
+        }
+        return true;
+    }
+
+    bool VisitReturnStmt(ReturnStmt const * stmt) {
+        if (ignoreLocation(stmt)) {
+            return true;
+        }
+        assert(!returnTypes_.empty());
+        if (!loplugin::TypeCheck(returnTypes_.top()).LvalueReference().Const())
+        {
+            return true;
+        }
+        auto const ret = stmt->getRetValue();
+        if (ret == nullptr) {
+            return true;
+        }
+        recordConsumption(lookThroughInitListExpr(ret));
+        return true;
+    }
+
+    bool VisitVarDecl(VarDecl const * decl) {
+        if (ignoreLocation(decl)) {
+            return true;
+        }
+        if (!loplugin::TypeCheck(decl->getType()).LvalueReference()) {
+            return true;
+        }
+        auto const init = decl->getInit();
+        if (init == nullptr) {
+            return true;
+        }
+        recordConsumption(lookThroughInitListExpr(init));
+        return true;
+    }
+
+    bool VisitFieldDecl(FieldDecl const * decl) {
+        if (ignoreLocation(decl)) {
+            return true;
+        }
+        if (!loplugin::TypeCheck(decl->getType()).LvalueReference()) {
+            return true;
+        }
+        auto const init = decl->getInClassInitializer();
+        if (init == nullptr) {
+            return true;
+        }
+        recordConsumption(lookThroughInitListExpr(init));
+        return true;
+    }
+
+private:
+    struct Usage {
+        std::vector<ExplicitCastExpr const *> castToVoid;
+        bool mentioned = false;
+        DeclRefExpr const * firstConsumption = nullptr;
+    };
+
+    struct CastToVoid {
+        ExplicitCastExpr const * cast;
+        DeclRefExpr const * sub;
+    };
+
+    std::map<VarDecl const *, Usage> vars_;
+    std::stack<CastToVoid> castToVoid_;
+    std::stack<QualType> returnTypes_;
+
+    void run() override {
+        if (!TraverseDecl(compiler.getASTContext().getTranslationUnitDecl())) {
+            return;
+        }
+        for (auto const & i: vars_) {
+            if (i.second.firstConsumption == nullptr) {
+                if (i.second.mentioned) {
+                    continue;
+                }
+                if (isa<ParmVarDecl>(i.first)) {
+                    if (!compiler.getLangOpts().CPlusPlus
+                        || isSharedCAndCppCode(i.first))
+                    {
+                        continue;
+                    }
+                    auto const fun = dyn_cast_or_null<FunctionDecl>(
+                        i.first->getDeclContext());
+                    assert(fun != nullptr);
+                    if (containsPreprocessingConditionalInclusion(
+                            fun->getSourceRange()))
+                    {
+                        continue;
+                    }
+                    auto const meth = dyn_cast<CXXMethodDecl>(fun);
+                    report(
+                        DiagnosticsEngine::Warning,
+                        "unused%select{| virtual function}0 parameter name",
+                        i.first->getLocation())
+                        << (meth != nullptr && meth->isVirtual())
+                        << i.first->getSourceRange();
+                    for (auto const j: i.second.castToVoid) {
+                        report(
+                            DiagnosticsEngine::Note, "cast to void here",
+                            j->getExprLoc())
+                            << j->getSourceRange();
+                    }
+                } else if (!i.second.castToVoid.empty()
+                           && !isWarnUnusedType(i.first->getType()))
+                {
+                    report(
+                        DiagnosticsEngine::Warning,
+                        "unused variable %select{declaration|name}0",
+                        i.first->getLocation())
+                        << i.first->isExceptionVariable()
+                        << i.first->getSourceRange();
+                    for (auto const j: i.second.castToVoid) {
+                        report(
+                            DiagnosticsEngine::Note, "cast to void here",
+                            j->getExprLoc())
+                            << j->getSourceRange();
+                    }
+                }
+            } else {
+                for (auto const j: i.second.castToVoid) {
+                    report(
+                        DiagnosticsEngine::Warning, "unnecessary cast to void",
+                        j->getExprLoc())
+                        << j->getSourceRange();
+                    report(
+                        DiagnosticsEngine::Note, "first consumption is here",
+                        i.second.firstConsumption->getExprLoc())
+                        << i.second.firstConsumption->getSourceRange();
+                }
+            }
+        }
+    }
+
+    bool isFromCIncludeFile(SourceLocation spellingLocation) const {
+        return !compiler.getSourceManager().isInMainFile(spellingLocation)
+            && (StringRef(
+                    compiler.getSourceManager().getPresumedLoc(spellingLocation)
+                    .getFilename())
+                .endswith(".h"));
+    }
+
+    bool isSharedCAndCppCode(VarDecl const * decl) const {
+        auto loc = decl->getLocStart();
+        while (compiler.getSourceManager().isMacroArgExpansion(loc)) {
+            loc = compiler.getSourceManager().getImmediateMacroCallerLoc(loc);
+        }
+        // Assume that code is intended to be shared between C and C++ if it
+        // comes from an include file ending in .h, and is either in an extern
+        // "C" context or the body of a macro definition:
+        return
+            isFromCIncludeFile(compiler.getSourceManager().getSpellingLoc(loc))
+            && (decl->isInExternCContext()
+                || compiler.getSourceManager().isMacroBodyExpansion(loc));
+    }
+
+    bool containsPreprocessingConditionalInclusion(SourceRange range) {
+        auto hash = false;
+        for (auto loc = range.getBegin();;) {
+            Token tok;
+            if (Lexer::getRawToken(
+                    loc, tok, compiler.getSourceManager(),
+                    compiler.getLangOpts(), true))
+            {
+                // Conservatively assume "yes" if lexing fails (e.g., due to
+                // macros):
+                return true;
+            }
+            if (hash && tok.is(tok::raw_identifier)) {
+                auto const id = tok.getRawIdentifier();
+                if (id == "if" || id == "ifdef" || id == "ifndef"
+                    || id == "elif" || id == "else" || id == "endif")
+                {
+                    return true;
+                }
+            }
+            if (loc == range.getEnd()) {
+                break;
+            }
+            hash = tok.is(tok::hash) && tok.isAtStartOfLine();
+            loc = loc.getLocWithOffset(
+                std::max<unsigned>(
+                    Lexer::MeasureTokenLength(
+                        loc, compiler.getSourceManager(),
+                        compiler.getLangOpts()),
+                    1));
+        }
+        return false;
+    }
+
+    DeclRefExpr const * checkCast(ExplicitCastExpr const * expr) {
+        if (!loplugin::TypeCheck(expr->getTypeAsWritten()).Void()) {
+            return nullptr;
+        }
+        if (compiler.getSourceManager().isMacroBodyExpansion(
+                expr->getLocStart()))
+        {
+            return nullptr;
+        }
+        return dyn_cast<DeclRefExpr>(expr->getSubExpr()->IgnoreParenImpCasts());
+    }
+
+    void recordConsumption(Expr const * expr) {
+        for (;;) {
+            expr = expr->IgnoreParenImpCasts();
+            if (auto const e = dyn_cast<MemberExpr>(expr)) {
+                expr = e->getBase();
+                continue;
+            }
+            if (auto const e = dyn_cast<ArraySubscriptExpr>(expr)) {
+                expr = e->getBase();
+                continue;
+            }
+            if (auto const e = dyn_cast<BinaryOperator>(expr)) {
+                if (e->getOpcode() == BO_PtrMemD) {
+                    expr = e->getLHS();
+                    continue;
+                }
+            }
+            break;
+        }
+        auto const dre = dyn_cast<DeclRefExpr>(expr);
+        if (dre == nullptr) {
+            return;
+        }
+        // In C (but not in C++)
+        //
+        //   (void) x
+        //
+        // contains an implicit lvalue-to-rvalue cast, so VisitImplicitCastExpr
+        // would record that as a consumption if we didn't filter it out here:
+        if (!castToVoid_.empty() && castToVoid_.top().sub == dre) {
+            return;
+        }
+        auto const var = dyn_cast<VarDecl>(dre->getDecl());
+        if (var == nullptr) {
+            return;
+        }
+        auto & usage = vars_[var->getCanonicalDecl()];
+        if (usage.firstConsumption != nullptr) {
+            return;
+        }
+        auto const loc = dre->getLocStart();
+        if (compiler.getSourceManager().isMacroArgExpansion(loc)
+            && (compat::getImmediateMacroNameForDiagnostics(
+                    loc, compiler.getSourceManager(), compiler.getLangOpts())
+                == "assert"))
+        {
+            return;
+        }
+        usage.firstConsumption = dre;
+    }
+};
+
+static loplugin::Plugin::Registration<Visitor> reg("casttovoid");
+
+}
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab cinoptions=b1,g0,N-s cinkeys+=0=break: */