New loplugin:selfinit

...to find more bugs like the one addressed in
6340daac "Revert broken
loplugin:sequentialassign change".  What it does is:  "Warn when a variable is
referenced from its own initializer.  This is not invalid in general (see C++17
[basic.life]), but is at least suspicious."  It found one false positive
(addressed with 884ad0d1 "Split
localProcessFactory function into class with setter and getter") and five true
positives (addressed with e0ccbe72 "Fix use of
variable before its lifetime begins" and
0e335af4 "Fix uses of variables before their
lifetimes begin").

Change-Id: I4c45cceaa042e93b37ad24a54784c027f6ca1f87
Reviewed-on: https://gerrit.libreoffice.org/70897
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

compilerplugins/clang/selfinit.cxx

+/* -*- 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 <vector>
+
+#include "plugin.hxx"
+
+// Warn when a variable is referenced from its own initializer.  This is not invalid in general (see
+// C++17 [basic.life]), but is at least suspicious.
+
+namespace
+{
+class SelfInit : public loplugin::FilteringPlugin<SelfInit>
+{
+public:
+    explicit SelfInit(loplugin::InstantiationData const& data)
+        : FilteringPlugin(data)
+    {
+    }
+
+    bool TraverseVarDecl(VarDecl* decl)
+    {
+        decls_.push_back({ decl, decl->getCanonicalDecl() });
+        auto const ret = FilteringPlugin::TraverseVarDecl(decl);
+        decls_.pop_back();
+        return ret;
+    }
+
+    bool TraverseUnaryExprOrTypeTraitExpr(UnaryExprOrTypeTraitExpr* expr)
+    {
+        if (expr->getKind() == UETT_SizeOf)
+        {
+            return true;
+        }
+        return FilteringPlugin::TraverseUnaryExprOrTypeTraitExpr(expr);
+    }
+
+    bool TraverseCXXTypeidExpr(CXXTypeidExpr const*) { return true; }
+
+    bool TraverseCXXNoexceptExpr(CXXNoexceptExpr const*) { return true; }
+
+    bool TraverseDecltypeTypeLoc(DecltypeTypeLoc) { return true; }
+
+    bool VisitDeclRefExpr(DeclRefExpr const* expr)
+    {
+        if (ignoreLocation(expr))
+        {
+            return true;
+        }
+        for (auto const& i : decls_)
+        {
+            if (expr->getDecl()->getCanonicalDecl() == i.canonical)
+            {
+                report(
+                    DiagnosticsEngine::Warning,
+                    ("referencing a variable during its own initialization is error-prone and thus"
+                     " suspicious"),
+                    expr->getLocation())
+                    << expr->getSourceRange();
+                report(DiagnosticsEngine::Note, "variable declared here", i.current->getLocation())
+                    << i.current->getSourceRange();
+            }
+        }
+        return true;
+    }
+
+private:
+    void run() override { TraverseDecl(compiler.getASTContext().getTranslationUnitDecl()); }
+
+    struct Decl
+    {
+        VarDecl const* current;
+        VarDecl const* canonical;
+    };
+
+    std::vector<Decl> decls_;
+};
+
+loplugin::Plugin::Registration<SelfInit> X("selfinit");
+}
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab cinoptions=b1,g0,N-s cinkeys+=0=break: */

compilerplugins/clang/test/selfinit.cxx

+/* -*- 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 <typeinfo>
+
+extern int i;
+int i = i;
+// expected-error@-1 {{referencing a variable during its own initialization is error-prone and thus suspicious [loplugin:selfinit]}}
+// expected-note@-2 {{variable declared here [loplugin:selfinit]}}
+
+int j = [](int n) { return j + n; }(0);
+// expected-error@-1 {{referencing a variable during its own initialization is error-prone and thus suspicious [loplugin:selfinit]}}
+// expected-note@-2 {{variable declared here [loplugin:selfinit]}}
+
+int k = sizeof k;
+
+int f(std::type_info const&);
+
+int l = f(typeid(l));
+
+bool m = noexcept(m);
+
+template <typename T> int g();
+
+int n = g<decltype(n)>();
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab cinoptions=b1,g0,N-s cinkeys+=0=break: */

solenv/CompilerTest_compilerplugins_clang.mk

@@ -51,6 +51,7 @@ $(eval $(call gb_CompilerTest_add_exception_objects,compilerplugins_clang, \
     compilerplugins/clang/test/salcall \
     compilerplugins/clang/test/sallogareas \
     compilerplugins/clang/test/salunicodeliteral \
+    compilerplugins/clang/test/selfinit \
     compilerplugins/clang/test/sequentialassign \
     compilerplugins/clang/test/shouldreturnbool \
     compilerplugins/clang/test/simplifybool \