A more lightweight O[U]StringConcatenation

...compared to a full-blown O[U]String, for temporary objects holding an
O[U]StringConcat result that can then be used as a std::[u16]string_view.

It's instructive to see how some invocations of operator ==, operator !=, and
O[U]StringBuffer::insert with an O[U]StringConcat argument required implicit
materialization of an O[U]String temporary, and how that expensive operation has
now been made explicit with the explicit O[U]StringConcatenation ctor.

(The additional operator == and operator != overloads are necessary because the
overloads taking two std::[u16]string_view parameters wouldn't even be found
here with ADL.  And the OUString-related ones would cause ambiguities in at
least sal/qa/rtl/strings/test_oustring_stringliterals.cxx built with
RTL_STRING_UNITTEST, so have simply been disabled for that special test-code
case.)

Change-Id: Id29799fa8da21a09ff9794cbc7cc9b366e6803b8
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/122890
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

2 files changed, 24 insertions, 6 deletions

diff --git a/compilerplugins/clang/stringview.cxx b/compilerplugins/clang/stringview.cxx
index 0c060ce93513..4043d7a67e60 100644
--- a/compilerplugins/clang/stringview.cxx
+++ b/compilerplugins/clang/stringview.cxx
@@ -162,7 +162,13 @@ void StringView::handleSubExprThatCouldBeView(Expr const* subExpr)
 void StringView::handleCXXConstructExpr(CXXConstructExpr const* expr)
 {
     QualType argType;
-    bool charArg = false;
+    enum
+    {
+        None,
+        OrChar,
+        ViaConcatenation
+    } extra
+        = None;
     auto const d = expr->getConstructor();
     switch (d->getNumParams())
     {
@@ -174,7 +180,7 @@ void StringView::handleCXXConstructExpr(CXXConstructExpr const* expr)
             if (t->isAnyCharacterType())
             {
                 argType = expr->getArg(0)->IgnoreImplicit()->getType();
-                charArg = true;
+                extra = OrChar;
                 break;
             }
             loplugin::TypeCheck tc(t);
@@ -195,6 +201,13 @@ void StringView::handleCXXConstructExpr(CXXConstructExpr const* expr)
                 argType = expr->getArg(0)->IgnoreImplicit()->getType();
                 break;
             }
+            if (tc.RvalueReference().Struct("OStringConcat").Namespace("rtl").GlobalNamespace()
+                || tc.RvalueReference().Struct("OUStringConcat").Namespace("rtl").GlobalNamespace())
+            {
+                argType = expr->getArg(0)->IgnoreImplicit()->getType();
+                extra = ViaConcatenation;
+                break;
+            }
             return;
         }
         case 2:
@@ -214,7 +227,7 @@ void StringView::handleCXXConstructExpr(CXXConstructExpr const* expr)
                         {
                             if (val->getExtValue() == 1)
                             {
-                                charArg = true;
+                                extra = OrChar;
                             }
                         }
                     }
@@ -239,13 +252,14 @@ void StringView::handleCXXConstructExpr(CXXConstructExpr const* expr)
     report(DiagnosticsEngine::Warning,
            "instead of an %0%select{| constructed from a %2}1, pass a"
            " '%select{std::string_view|std::u16string_view}3'"
-           "%select{| (or an '%select{rtl::OStringChar|rtl::OUStringChar}3')}4",
+           "%select{| (or an '%select{rtl::OStringChar|rtl::OUStringChar}3')|"
+           " via '%select{rtl::OStringConcatenation|rtl::OUStringConcatenation}3'}4",
            expr->getExprLoc())
         << expr->getType() << (argType.isNull() ? 0 : 1) << argType
         << (loplugin::TypeCheck(expr->getType()).Class("OString").Namespace("rtl").GlobalNamespace()
                 ? 0
                 : 1)
-        << charArg << expr->getSourceRange();
+        << extra << expr->getSourceRange();
 }
 
 void StringView::handleCXXMemberCallExpr(CXXMemberCallExpr const* expr)
diff --git a/compilerplugins/clang/test/stringview.cxx b/compilerplugins/clang/test/stringview.cxx
index 34accb6e6448..be7b8db3ea95 100644
--- a/compilerplugins/clang/test/stringview.cxx
+++ b/compilerplugins/clang/test/stringview.cxx
@@ -99,7 +99,7 @@ void f4(OUString s1, OUString s2)
 }
 }
 
-void f5(char const* s1, sal_Int32 n1, char16_t const* s2, sal_Int32 n2)
+void f5(char const* s1, sal_Int32 n1, char16_t const* s2, sal_Int32 n2, OString s3, OUString s4)
 {
     // expected-error@+1 {{instead of an 'rtl::OString', pass a 'std::string_view' [loplugin:stringview]}}
     call_view(OString());
@@ -118,6 +118,8 @@ void f5(char const* s1, sal_Int32 n1, char16_t const* s2, sal_Int32 n2)
     call_view(OString(std::string_view("foo")));
     // expected-error@+1 {{instead of an 'rtl::OString' constructed from a 'OStringNumber<int>', pass a 'std::string_view' [loplugin:stringview]}}
     call_view(OString(OString::number(0)));
+    // expected-error-re@+1 {{instead of an 'rtl::OString' constructed from a 'typename std::enable_if_t<ToStringHelper<OString>::allowOStringConcat && ToStringHelper<OString>::allowOStringConcat, OStringConcat<OString, OString>{{ ?}}>' (aka 'rtl::OStringConcat<rtl::OString, rtl::OString>'), pass a 'std::string_view' via 'rtl::OStringConcatenation' [loplugin:stringview]}}
+    call_view(OString(s3 + s3));
     // expected-error@+1 {{instead of an 'rtl::OUString', pass a 'std::u16string_view' [loplugin:stringview]}}
     call_view(OUString());
     // expected-error@+1 {{instead of an 'rtl::OUString' constructed from a 'const char [4]', pass a 'std::u16string_view' [loplugin:stringview]}}
@@ -141,6 +143,8 @@ void f5(char const* s1, sal_Int32 n1, char16_t const* s2, sal_Int32 n2)
     call_view(OUString(std::u16string_view(u"foo")));
     // expected-error@+1 {{instead of an 'rtl::OUString' constructed from a 'OUStringNumber<int>', pass a 'std::u16string_view' [loplugin:stringview]}}
     call_view(OUString(OUString::number(0)));
+    // expected-error-re@+1 {{instead of an 'rtl::OUString' constructed from a 'typename std::enable_if_t<ToStringHelper<OUString>::allowOUStringConcat && ToStringHelper<OUString>::allowOUStringConcat, OUStringConcat<OUString, OUString>{{ ?}}>' (aka 'rtl::OUStringConcat<rtl::OUString, rtl::OUString>'), pass a 'std::u16string_view' via 'rtl::OUStringConcatenation' [loplugin:stringview]}}
+    call_view(OUString(s4 + s4));
 }
 
 void f5(OUString s)