loplugin:stringview

Add new methods "subView" to O(U)String to return substring views
of the underlying data.

Add a clang plugin to warn when replacing existing calls to copy()
would be better to use subView().

Change-Id: I03a5732431ce60808946f2ce2c923b22845689ca
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/105420
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>

2 files changed, 284 insertions, 0 deletions

diff --git a/compilerplugins/clang/stringview.cxx b/compilerplugins/clang/stringview.cxx
new file mode 100644
index 000000000000..530cf43d95a0
--- /dev/null
+++ b/compilerplugins/clang/stringview.cxx
@@ -0,0 +1,188 @@
+/* -*- 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 "clang/AST/CXXInheritance.h"
+#include "clang/AST/StmtVisitor.h"
+
+/**
+    Look for places where we are making a substring copy of an OUString, and then passing it to a
+    function that takes a u16string_view, in which case it is more efficient to pass a view
+    of the OUString, rather than making a copy.
+
+    TODO currently does not check if there is some other visible overload of the callee, that can take
+    a string_view.
+    TODO handle OUStringBuffer/OStringBuffer similarly
+*/
+
+namespace
+{
+class StringView : public loplugin::FilteringPlugin<StringView>
+{
+public:
+    explicit StringView(loplugin::InstantiationData const& data)
+        : FilteringPlugin(data)
+    {
+    }
+
+    bool preRun() override { return true; }
+
+    virtual void run() override
+    {
+        if (!preRun())
+            return;
+        TraverseDecl(compiler.getASTContext().getTranslationUnitDecl());
+    }
+
+    bool VisitCallExpr(CallExpr const*);
+    bool VisitCXXConstructExpr(CXXConstructExpr const*);
+    bool VisitFunctionDecl(FunctionDecl const*);
+    bool VisitCXXOperatorCallExpr(CXXOperatorCallExpr const*);
+};
+
+bool StringView::VisitCallExpr(CallExpr const* callExpr)
+{
+    if (ignoreLocation(callExpr))
+        return true;
+
+    const FunctionDecl* functionDecl;
+    if (isa<CXXMemberCallExpr>(callExpr))
+        functionDecl = dyn_cast<CXXMemberCallExpr>(callExpr)->getMethodDecl();
+    else
+        functionDecl = callExpr->getDirectCallee();
+    if (!functionDecl)
+        return true;
+
+    unsigned len = std::min(callExpr->getNumArgs(), functionDecl->getNumParams());
+    for (unsigned i = 0; i < len; ++i)
+    {
+        const Expr* argExpr = callExpr->getArg(i);
+        auto paramDecl = functionDecl->getParamDecl(i);
+        auto paramRecordDecl = dyn_cast_or_null<RecordDecl>(
+            paramDecl->getType()->getUnqualifiedDesugaredType()->getAsTagDecl());
+        if (!paramRecordDecl || !paramRecordDecl->getIdentifier()
+            || paramRecordDecl->getName() != "basic_string_view")
+            continue;
+        // unwrap the operator that converts to std::u16string_view
+        auto memberCallExpr = dyn_cast<CXXMemberCallExpr>(argExpr->IgnoreImpCasts());
+        if (!memberCallExpr)
+            continue;
+        // unwrap the call to copy()
+        auto memberCallExpr2 = dyn_cast<CXXMemberCallExpr>(
+            compat::IgnoreImplicit(memberCallExpr->getImplicitObjectArgument()));
+        if (!memberCallExpr2)
+            continue;
+        auto methodDecl = memberCallExpr2->getMethodDecl();
+        if (!methodDecl->getIdentifier() || methodDecl->getName() != "copy")
+            continue;
+        report(DiagnosticsEngine::Warning, "rather than copy, pass with a view using subView()",
+               compat::getBeginLoc(argExpr))
+            << argExpr->getSourceRange();
+    }
+
+    return true;
+}
+
+bool StringView::VisitCXXOperatorCallExpr(CXXOperatorCallExpr const* cxxOperatorCallExpr)
+{
+    if (ignoreLocation(cxxOperatorCallExpr))
+        return true;
+
+    auto check = [&](const Expr* expr) -> void {
+        auto memberCallExpr = dyn_cast<CXXMemberCallExpr>(compat::IgnoreImplicit(expr));
+        if (!memberCallExpr)
+            return;
+        auto methodDecl = memberCallExpr->getMethodDecl();
+        if (!methodDecl->getIdentifier() || methodDecl->getName() != "copy")
+            return;
+        report(DiagnosticsEngine::Warning, "rather than copy, pass with a view using subView()",
+               compat::getBeginLoc(expr))
+            << expr->getSourceRange();
+    };
+    auto op = cxxOperatorCallExpr->getOperator();
+    if (op == OO_Plus && cxxOperatorCallExpr->getNumArgs() == 2)
+    {
+        check(cxxOperatorCallExpr->getArg(0));
+        check(cxxOperatorCallExpr->getArg(1));
+    }
+    if (compat::isComparisonOp(cxxOperatorCallExpr))
+    {
+        check(cxxOperatorCallExpr->getArg(0));
+        check(cxxOperatorCallExpr->getArg(1));
+    }
+    else if (op == OO_PlusEqual)
+        check(cxxOperatorCallExpr->getArg(1));
+    else if (op == OO_Subscript)
+        check(cxxOperatorCallExpr->getArg(0));
+    return true;
+}
+
+bool StringView::VisitFunctionDecl(FunctionDecl const* functionDecl)
+{
+    if (ignoreLocation(functionDecl))
+        return true;
+    // debugging
+    // if (functionDecl->getIdentifier() && functionDecl->getName() == "f1")
+    //     functionDecl->dump();
+    return true;
+}
+
+bool StringView::VisitCXXConstructExpr(CXXConstructExpr const* constructExpr)
+{
+    if (ignoreLocation(constructExpr))
+        return true;
+
+    const CXXConstructorDecl* constructorDecl = constructExpr->getConstructor();
+    if (!constructorDecl)
+        return true;
+
+    unsigned len = std::min(constructExpr->getNumArgs(), constructorDecl->getNumParams());
+    for (unsigned i = 0; i < len; ++i)
+    {
+        const Expr* argExpr = constructExpr->getArg(i);
+        auto paramDecl = constructorDecl->getParamDecl(i);
+        auto paramRecordDecl = dyn_cast_or_null<RecordDecl>(
+            paramDecl->getType()->getUnqualifiedDesugaredType()->getAsTagDecl());
+        if (!paramRecordDecl || !paramRecordDecl->getIdentifier()
+            || paramRecordDecl->getName() != "basic_string_view")
+            continue;
+        // unwrap the operator that converts to std::u16string_view
+        auto memberCallExpr = dyn_cast<CXXMemberCallExpr>(argExpr->IgnoreImpCasts());
+        if (!memberCallExpr)
+            continue;
+        // unwrap the call to copy()
+        auto memberCallExpr2 = dyn_cast<CXXMemberCallExpr>(
+            compat::IgnoreImplicit(memberCallExpr->getImplicitObjectArgument()));
+        if (!memberCallExpr2)
+            continue;
+        auto methodDecl = memberCallExpr2->getMethodDecl();
+        if (!methodDecl->getIdentifier() || methodDecl->getName() != "copy")
+            continue;
+        report(DiagnosticsEngine::Warning, "rather than copy, pass with a view using subView()",
+               compat::getBeginLoc(argExpr))
+            << argExpr->getSourceRange();
+    }
+
+    return true;
+}
+
+loplugin::Plugin::Registration<StringView> stringview("stringview");
+}
+
+#endif // LO_CLANG_SHARED_PLUGINS
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */
diff --git a/compilerplugins/clang/test/stringview.cxx b/compilerplugins/clang/test/stringview.cxx
new file mode 100644
index 000000000000..96d4927e533a
--- /dev/null
+++ b/compilerplugins/clang/test/stringview.cxx
@@ -0,0 +1,96 @@
+/* -*- 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 <rtl/strbuf.hxx>
+#include <rtl/string.hxx>
+#include <rtl/ustrbuf.hxx>
+#include <rtl/ustring.hxx>
+
+void call_view(std::u16string_view) {}
+void call_view(std::string_view) {}
+struct ConstructWithView
+{
+    ConstructWithView(std::u16string_view) {}
+    ConstructWithView(std::string_view) {}
+};
+
+namespace test1
+{
+void f1(std::u16string_view s1)
+{
+    // no warning expected
+    call_view(s1);
+}
+void f1(std::string_view s1)
+{
+    // no warning expected
+    call_view(s1);
+}
+void f1(OUString s1)
+{
+    // expected-error@+1 {{rather than copy, pass with a view using subView() [loplugin:stringview]}}
+    call_view(s1.copy(1, 2));
+    // expected-error@+1 {{rather than copy, pass with a view using subView() [loplugin:stringview]}}
+    call_view(s1.copy(1));
+    // expected-error@+1 {{rather than copy, pass with a view using subView() [loplugin:stringview]}}
+    ConstructWithView(s1.copy(1, 2));
+    // expected-error@+1 {{rather than copy, pass with a view using subView() [loplugin:stringview]}}
+    ConstructWithView(s1.copy(1));
+}
+void f1(OString s1)
+{
+    // expected-error@+1 {{rather than copy, pass with a view using subView() [loplugin:stringview]}}
+    call_view(s1.copy(1, 2));
+    // expected-error@+1 {{rather than copy, pass with a view using subView() [loplugin:stringview]}}
+    call_view(s1.copy(1));
+    // expected-error@+1 {{rather than copy, pass with a view using subView() [loplugin:stringview]}}
+    ConstructWithView(s1.copy(1, 2));
+    // expected-error@+1 {{rather than copy, pass with a view using subView() [loplugin:stringview]}}
+    ConstructWithView(s1.copy(1));
+}
+}
+
+namespace test2
+{
+void f3(OUString s1)
+{
+    // expected-error@+1 {{rather than copy, pass with a view using subView() [loplugin:stringview]}}
+    OUString s2 = s1.copy(1, 2) + "xxx";
+    // expected-error@+1 {{rather than copy, pass with a view using subView() [loplugin:stringview]}}
+    s2 = s1.copy(1) + "xxx";
+    // expected-error@+1 {{rather than copy, pass with a view using subView() [loplugin:stringview]}}
+    s2 = "xxx" + s1.copy(1);
+    // expected-error@+1 {{rather than copy, pass with a view using subView() [loplugin:stringview]}}
+    s2 += s1.copy(1);
+}
+void f3(OString s1)
+{
+    // expected-error@+1 {{rather than copy, pass with a view using subView() [loplugin:stringview]}}
+    OString s2 = s1.copy(1, 2) + "xxx";
+    (void)s2;
+    // expected-error@+1 {{rather than copy, pass with a view using subView() [loplugin:stringview]}}
+    OString s3 = s1.copy(1) + "xxx";
+    (void)s3;
+}
+}
+
+namespace test3
+{
+void f4(OUString s1, OUString s2)
+{
+    // expected-error@+1 {{rather than copy, pass with a view using subView() [loplugin:stringview]}}
+    sal_Unicode x = s2.copy(1, 2)[12];
+    (void)x;
+    // expected-error@+1 {{rather than copy, pass with a view using subView() [loplugin:stringview]}}
+    if (s2.copy(1, 2) < s1)
+        ;
+}
+}
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab cinoptions=b1,g0,N-s cinkeys+=0=break: */