loplugin:stringview: Flag empty string converted to string view

Change-Id: Idf412dc5f235230512160cb4fb7e1a00baa1cfa7
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/106085
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

2 files changed, 42 insertions, 0 deletions

diff --git a/compilerplugins/clang/stringview.cxx b/compilerplugins/clang/stringview.cxx
index 530cf43d95a0..5a70d01de841 100644
--- a/compilerplugins/clang/stringview.cxx
+++ b/compilerplugins/clang/stringview.cxx
@@ -52,6 +52,7 @@ public:
     bool VisitCXXConstructExpr(CXXConstructExpr const*);
     bool VisitFunctionDecl(FunctionDecl const*);
     bool VisitCXXOperatorCallExpr(CXXOperatorCallExpr const*);
+    bool VisitImplicitCastExpr(ImplicitCastExpr const*);
 };
 
 bool StringView::VisitCallExpr(CallExpr const* callExpr)
@@ -180,6 +181,39 @@ bool StringView::VisitCXXConstructExpr(CXXConstructExpr const* constructExpr)
     return true;
 }
 
+bool StringView::VisitImplicitCastExpr(ImplicitCastExpr const* expr)
+{
+    if (ignoreLocation(expr))
+    {
+        return true;
+    }
+    if (!loplugin::TypeCheck(expr->getType()).ClassOrStruct("basic_string_view").StdNamespace())
+    {
+        return true;
+    }
+    auto const e = dyn_cast<CXXConstructExpr>(expr->getSubExprAsWritten()->IgnoreParens());
+    if (e == nullptr)
+    {
+        return true;
+    }
+    if (e->getNumArgs() != 0)
+    {
+        return true;
+    }
+    auto const tc = loplugin::TypeCheck(e->getType());
+    if (!(tc.Class("OString").Namespace("rtl").GlobalNamespace()
+          || tc.Class("OUString").Namespace("rtl").GlobalNamespace()))
+    {
+        return true;
+    }
+    report(DiagnosticsEngine::Warning,
+           "instead of an empty %0, pass an empty '%select{std::string_view|std::u16string_view}1'",
+           e->getLocation())
+        << e->getType() << (tc.Class("OString").Namespace("rtl").GlobalNamespace() ? 0 : 1)
+        << e->getSourceRange();
+    return true;
+}
+
 loplugin::Plugin::Registration<StringView> stringview("stringview");
 }
 
diff --git a/compilerplugins/clang/test/stringview.cxx b/compilerplugins/clang/test/stringview.cxx
index 96d4927e533a..3c15d9cc4437 100644
--- a/compilerplugins/clang/test/stringview.cxx
+++ b/compilerplugins/clang/test/stringview.cxx
@@ -93,4 +93,12 @@ void f4(OUString s1, OUString s2)
 }
 }
 
+void f5()
+{
+    // expected-error@+1 {{instead of an empty 'rtl::OString', pass an empty 'std::string_view' [loplugin:stringview]}}
+    call_view(OString());
+    // expected-error@+1 {{instead of an empty 'rtl::OUString', pass an empty 'std::u16string_view' [loplugin:stringview]}}
+    call_view(OUString());
+}
+
 /* vim:set shiftwidth=4 softtabstop=4 expandtab cinoptions=b1,g0,N-s cinkeys+=0=break: */