New loplugin:stdfunction

...finding dubious additions to namespace std (concentrating on functions for
now).  C++17 [namespace.std]/1: "The behavior of a C ++ program is undefined if
it adds declarations or definitions to namespace std or to a namespace within
namespace std unless otherwise specified."

This found

ad4c7b97752b4da73808402604d6f96b39d920f5 "Avoid declaring function templates in
 namespace std"
042e30a3dc057aef4a02d95960e4dd4fb8d083ae "Avoid adding a function template
 declaration to namespace std"
cae9240a76cdb0eeed92421930d3b4cbef0ac201 "Avoid adding a function declaration to
 namespace std"

Change-Id: Ic2ba54e2a8bf931d5c58cedf499c0d1229eb2166
Reviewed-on: https://gerrit.libreoffice.org/78220
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

4 files changed, 141 insertions, 13 deletions

diff --git a/compilerplugins/clang/check.cxx b/compilerplugins/clang/check.cxx
index f2443e44a1f2..d53bfabbe9cf 100644
--- a/compilerplugins/clang/check.cxx
+++ b/compilerplugins/clang/check.cxx
@@ -151,12 +151,17 @@ ContextCheck DeclCheck::MemberFunction() const {
     return ContextCheck(m == nullptr ? nullptr : m->getParent());
 }
 
+namespace {
+
+bool isGlobalNamespace(clang::DeclContext const * context) {
+    assert(context != nullptr);
+    return (context->isLookupContext() ? context : context->getLookupParent())->isTranslationUnit();
+}
+
+}
+
 TerminalCheck ContextCheck::GlobalNamespace() const {
-    return TerminalCheck(
-        context_ != nullptr
-        && ((context_->isLookupContext()
-             ? context_ : context_->getLookupParent())
-            ->isTranslationUnit()));
+    return TerminalCheck(context_ != nullptr && isGlobalNamespace(context_));
 }
 
 TerminalCheck ContextCheck::StdNamespace() const {
@@ -164,6 +169,28 @@ TerminalCheck ContextCheck::StdNamespace() const {
         context_ != nullptr && context_->isStdNamespace());
 }
 
+namespace {
+
+bool isStdOrNestedNamespace(clang::DeclContext const * context) {
+    assert(context != nullptr);
+    if (!context->isNamespace()) {
+        return false;
+    }
+    if (isGlobalNamespace(context)) {
+        return false;
+    }
+    if (context->isStdNamespace()) {
+        return true;
+    }
+    return isStdOrNestedNamespace(context->getParent());
+}
+
+}
+
+TerminalCheck ContextCheck::StdOrNestedNamespace() const {
+    return TerminalCheck(context_ != nullptr && isStdOrNestedNamespace(context_));
+}
+
 ContextCheck ContextCheck::AnonymousNamespace() const {
     auto n = llvm::dyn_cast_or_null<clang::NamespaceDecl>(context_);
     return ContextCheck(
diff --git a/compilerplugins/clang/check.hxx b/compilerplugins/clang/check.hxx
index 0904e5f2f1a1..4ac4f8e99cb6 100644
--- a/compilerplugins/clang/check.hxx
+++ b/compilerplugins/clang/check.hxx
@@ -103,6 +103,9 @@ private:
 
 class ContextCheck {
 public:
+    explicit ContextCheck(clang::DeclContext const * context = nullptr):
+        context_(context) {}
+
     explicit operator bool() const { return context_ != nullptr; }
 
     TerminalCheck GlobalNamespace() const;
@@ -111,6 +114,8 @@ public:
 
     TerminalCheck StdNamespace() const;
 
+    TerminalCheck StdOrNestedNamespace() const;
+
     ContextCheck AnonymousNamespace() const;
 
     inline ContextCheck Class(llvm::StringRef id) const;
@@ -120,14 +125,6 @@ public:
     explicit ContextCheck(const clang::NamespaceDecl * decl ) : context_( decl ) {}
 
 private:
-    friend DeclCheck;
-    friend TypeCheck;
-    friend ContextCheck detail::checkRecordDecl(
-        clang::Decl const * decl, clang::TagTypeKind tag, llvm::StringRef id);
-
-    explicit ContextCheck(clang::DeclContext const * context = nullptr):
-        context_(context) {}
-
     clang::DeclContext const * const context_;
 };
 
diff --git a/compilerplugins/clang/stdfunction.cxx b/compilerplugins/clang/stdfunction.cxx
new file mode 100644
index 000000000000..89935558d8a2
--- /dev/null
+++ b/compilerplugins/clang/stdfunction.cxx
@@ -0,0 +1,48 @@
+/* -*- 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 "check.hxx"
+#include "plugin.hxx"
+
+namespace
+{
+class StdFunction final : public loplugin::FilteringPlugin<StdFunction>
+{
+public:
+    explicit StdFunction(loplugin::InstantiationData const& data)
+        : FilteringPlugin(data)
+    {
+    }
+
+    bool VisitFunctionDecl(FunctionDecl const* decl)
+    {
+        if (ignoreLocation(decl))
+        {
+            return true;
+        }
+        if (!loplugin::ContextCheck(decl->getDeclContext()).StdOrNestedNamespace())
+        {
+            return true;
+        }
+        report(DiagnosticsEngine::Warning,
+               ("Do not declare a %select{function|function template|member function template"
+                " specialization|function template specialization}0 in namespace 'std'"),
+               decl->getLocation())
+            << decl->getTemplatedKind() << decl->getSourceRange();
+        return true;
+    }
+
+private:
+    void run() override { TraverseDecl(compiler.getASTContext().getTranslationUnitDecl()); }
+};
+
+static loplugin::Plugin::Registration<StdFunction> X("stdfunction");
+}
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab cinoptions=b1,g0,N-s cinkeys+=0=break: */
diff --git a/compilerplugins/clang/test/stdfunction.cxx b/compilerplugins/clang/test/stdfunction.cxx
new file mode 100644
index 000000000000..492ba4249f16
--- /dev/null
+++ b/compilerplugins/clang/test/stdfunction.cxx
@@ -0,0 +1,56 @@
+/* -*- 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 <iterator>
+#include <vector>
+
+struct S
+{
+    bool empty() const;
+};
+
+template <typename> struct ST
+{
+    bool empty() const;
+};
+
+namespace std
+{
+bool empty( //expected-error {{Do not declare a function in namespace 'std' [loplugin:stdfunction]}}
+    S const&);
+
+template <>
+bool empty( //expected-error {{Do not declare a function template specialization in namespace 'std' [loplugin:stdfunction]}}
+    S const&);
+
+template <typename T>
+bool empty( //expected-error {{Do not declare a function template in namespace 'std' [loplugin:stdfunction]}}
+    ST<T> const&);
+
+template <> class vector<S>
+{
+public:
+    [[nodiscard]] constexpr bool empty() const noexcept;
+};
+
+[[nodiscard]] constexpr bool vector<S>::empty() const noexcept { return true; }
+}
+
+namespace std::inner
+{
+bool empty( //expected-error {{Do not declare a function in namespace 'std' [loplugin:stdfunction]}}
+    S const&);
+}
+
+namespace outer::std
+{
+bool empty(S const&);
+}
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab cinoptions=b1,g0,N-s cinkeys+=0=break: */