new loplugin:stringviewdangle

to find places where string_view is pointing into a temporary String

Change-Id: Ib530b36f441e95d83d8f687d40a97516a0806721
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/133656
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>

2 files changed, 154 insertions, 0 deletions

diff --git a/compilerplugins/clang/stringviewdangle.cxx b/compilerplugins/clang/stringviewdangle.cxx
new file mode 100644
index 000000000000..99cb852d03b6
--- /dev/null
+++ b/compilerplugins/clang/stringviewdangle.cxx
@@ -0,0 +1,117 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/*
+ * 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/.
+ */
+#ifndef LO_CLANG_SHARED_PLUGINS
+
+#include <cassert>
+#include <string>
+#include <iostream>
+#include <unordered_map>
+#include <unordered_set>
+
+#include "plugin.hxx"
+#include "check.hxx"
+#include "compat.hxx"
+#include "config_clang.h"
+#include "clang/AST/CXXInheritance.h"
+#include "clang/AST/StmtVisitor.h"
+
+/**
+Look for places where we are assigning a temporary O[U]String to a std::*string_view, which leads
+to a view pointing to freed memory.
+*/
+
+namespace
+{
+class StringViewDangle : public loplugin::FilteringPlugin<StringViewDangle>
+{
+public:
+    explicit StringViewDangle(loplugin::InstantiationData const& data)
+        : FilteringPlugin(data)
+    {
+    }
+
+    bool preRun() override { return true; }
+
+    virtual void run() override
+    {
+        if (!preRun())
+            return;
+        TraverseDecl(compiler.getASTContext().getTranslationUnitDecl());
+    }
+
+    bool VisitCXXOperatorCallExpr(CXXOperatorCallExpr const*);
+    bool VisitVarDecl(VarDecl const*);
+};
+
+static const Expr* IgnoreImplicitAndConversionOperator(const Expr* expr)
+{
+    expr = expr->IgnoreImplicit();
+    if (auto memberCall = dyn_cast<CXXMemberCallExpr>(expr))
+    {
+        if (auto conversionDecl = dyn_cast_or_null<CXXConversionDecl>(memberCall->getMethodDecl()))
+        {
+            if (!conversionDecl->isExplicit())
+                expr = memberCall->getImplicitObjectArgument()->IgnoreImpCasts();
+        }
+    }
+    return expr;
+}
+
+bool StringViewDangle::VisitCXXOperatorCallExpr(CXXOperatorCallExpr const* cxxOperatorCallExpr)
+{
+    if (ignoreLocation(cxxOperatorCallExpr))
+        return true;
+
+    auto op = cxxOperatorCallExpr->getOperator();
+    if (op != OO_Equal)
+        return true;
+    if (!loplugin::TypeCheck(cxxOperatorCallExpr->getType())
+             .ClassOrStruct("basic_string_view")
+             .StdNamespace())
+        return true;
+    auto expr = IgnoreImplicitAndConversionOperator(cxxOperatorCallExpr->getArg(1));
+    auto tc = loplugin::TypeCheck(expr->getType());
+    if (!tc.Class("OUString").Namespace("rtl").GlobalNamespace()
+        && !tc.Class("OString").Namespace("rtl").GlobalNamespace())
+        return true;
+    if (!isa<MaterializeTemporaryExpr>(expr))
+        return true;
+    report(DiagnosticsEngine::Warning, "view pointing into temporary i.e. dangling",
+           cxxOperatorCallExpr->getExprLoc())
+        << cxxOperatorCallExpr->getSourceRange();
+    return true;
+}
+
+bool StringViewDangle::VisitVarDecl(VarDecl const* varDecl)
+{
+    if (ignoreLocation(varDecl))
+        return true;
+    if (!loplugin::TypeCheck(varDecl->getType()).ClassOrStruct("basic_string_view").StdNamespace())
+        return true;
+    if (!varDecl->hasInit())
+        return true;
+    auto expr = IgnoreImplicitAndConversionOperator(varDecl->getInit());
+    auto tc = loplugin::TypeCheck(expr->getType());
+    if (!tc.Class("OUString").Namespace("rtl").GlobalNamespace()
+        && !tc.Class("OString").Namespace("rtl").GlobalNamespace())
+        return true;
+    if (!isa<MaterializeTemporaryExpr>(expr))
+        return true;
+    report(DiagnosticsEngine::Warning, "view pointing into temporary i.e. dangling",
+           varDecl->getLocation())
+        << varDecl->getSourceRange();
+    return true;
+}
+
+loplugin::Plugin::Registration<StringViewDangle> stringviewdangle("stringviewdangle");
+}
+
+#endif // LO_CLANG_SHARED_PLUGINS
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */
diff --git a/compilerplugins/clang/test/stringviewdangle.cxx b/compilerplugins/clang/test/stringviewdangle.cxx
new file mode 100644
index 000000000000..0a8d2aa54b44
--- /dev/null
+++ b/compilerplugins/clang/test/stringviewdangle.cxx
@@ -0,0 +1,37 @@
+/* -*- 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 <sal/config.h>
+
+#include <string_view>
+#include <utility>
+
+#include <rtl/strbuf.hxx>
+#include <rtl/string.hxx>
+#include <rtl/ustrbuf.hxx>
+#include <rtl/ustring.hxx>
+#include <sal/types.h>
+
+namespace test1
+{
+OUString foo1();
+OUString& foo2();
+void f1()
+{
+    // expected-error@+1 {{view pointing into temporary i.e. dangling [loplugin:stringviewdangle]}}
+    std::u16string_view v = foo1();
+    // expected-error@+1 {{view pointing into temporary i.e. dangling [loplugin:stringviewdangle]}}
+    v = foo1();
+
+    // no warning expected
+    std::u16string_view v2 = foo2();
+    v2 = foo2();
+}
+}
+/* vim:set shiftwidth=4 softtabstop=4 expandtab cinoptions=b1,g0,N-s cinkeys+=0=break: */