Add AddAvailableCatalog() and use it in AddStdCatalog()

The new function only returns true if the catalog could be really
loaded and not if it is considered not to be needed because the message
ID language (which is typically "en-US") happens to be present in the
preferred UI languages list (which seems to always include "en-US" in at
least Western European MSW).

This allows to distinguish, albeit in a rather awkward (but
backwards-compatible) way between having a translation for the given
language and not needed such translation.

It is still not clear if it is really correct to return "en-US" from the
list of preferred languages even if the user has never intentionally
configured the OS to indicate that English is acceptable, but at least
now we can work around this issue and use AddAvailableCatalog() in
AddStdCatalog() to make sure we only skip loading unversioned wxstd.mo
if the versioned wxstd-x.y.mo file is really found instead of never
doing it, as was the case until now (see #23886).

Also add GetBestAvailableTranslation() helper which seems more useful
than the existing GetBestTranslation() one and is similarly related to
it.

See #18227.

include/wx/translation.h

@@ -151,16 +151,24 @@ class WXDLLIMPEXP_BASE wxTranslations
     // get languages available for this app
     wxArrayString GetAvailableTranslations(const wxString& domain) const;
 
-    // find best translation language for given domain
+    // find best available translation language for given domain
+    wxString GetBestAvailableTranslation(const wxString& domain);
+
     wxString GetBestTranslation(const wxString& domain, wxLanguage msgIdLanguage);
     wxString GetBestTranslation(const wxString& domain,
                                 const wxString& msgIdLanguage = wxASCII_STR("en"));
 
+    // add catalog for the given domain returning true if it could be found by
+    // wxTranslationsLoader
+    bool AddAvailableCatalog(const wxString& domain);
+
     // add standard wxWidgets catalog ("wxstd")
     bool AddStdCatalog();
 
     // add catalog with given domain name and language, looking it up via
-    // wxTranslationsLoader
+    // wxTranslationsLoader -- unlike AddAvailableCatalog(), this function also
+    // returns true if this catalog is not needed at all because msgIdLanguage
+    // is an acceptable language to use directly
     bool AddCatalog(const wxString& domain,
                     wxLanguage msgIdLanguage = wxLANGUAGE_ENGLISH_US);
 
@@ -186,7 +194,7 @@ class WXDLLIMPEXP_BASE wxTranslations
 
 private:
     // perform loading of the catalog via m_loader
-    bool LoadCatalog(const wxString& domain, const wxString& lang, const wxString& msgIdLang);
+    bool LoadCatalog(const wxString& domain, const wxString& lang);
 
     // find catalog by name in a linked list, return nullptr if !found
     wxMsgCatalog *FindCatalog(const wxString& domain) const;

interface/wx/translation.h

@@ -89,6 +89,18 @@ class wxTranslations
      */
     wxArrayString GetAvailableTranslations(const wxString& domain) const;
 
+    /**
+        Returns the best available translation for the required language.
+
+        For wxLANGUAGE_DEFAULT, this function returns the available translation
+        best matching one of wxUILocale::GetPreferredUILanguages(). Otherwise
+        it simply returns the language set with SetLanguage() if it's available
+        or empty string otherwise.
+
+        @since 3.3.0
+     */
+    wxString GetBestAvailableTranslation(const wxString& domain);
+
     /**
         Returns the best UI language for the @a domain.
 
@@ -98,6 +110,13 @@ class wxTranslations
         wxLocale::GetSystemLanguage() as operating systems have separate
         language and regional (i.e. locale) settings.
 
+        Please note that that this function may return the language
+        corresponding to @a msgIdLanguage if this language is considered to be
+        acceptable, i.e. is part of wxUILocale::GetPreferredUILanguages(),
+        indicating that it is fine not to use translations at all on this
+        system. If this is undesirable, GetBestAvailableTranslation() should be
+        used which doesn't consider the messages ID language as being available.
+
         @param domain
             The catalog domain to look for.
 
@@ -124,21 +143,43 @@ class wxTranslations
 
         @return @true if a suitable catalog was found, @false otherwise
 
-        @see AddCatalog()
+        @see AddAvailableCatalog()
      */
     bool AddStdCatalog();
 
     /**
         Add a catalog for use with the current locale.
 
-        By default, it is searched for in standard places (see
+        By default, the catalog is searched for in standard places (see
         wxFileTranslationsLoader), but you may also prepend additional
         directories to the search path with
         wxFileTranslationsLoader::AddCatalogLookupPathPrefix().
 
         All loaded catalogs will be used for message lookup by GetString() for
         the current locale.
 
+        @return
+            @true if catalog was successfully loaded, @false otherwise, usually
+            because it wasn't found. Note that unlike AddCatalog() this
+            function returns @false even if the language of the original
+            strings (usually English) can be used directly, i.e. its return
+            value only indicates that there are no catalogs available for the
+            selected or system-default languages, but is not necessarily an
+            error if no translations are needed in the first place.
+
+        @since 3.3.0
+     */
+    bool AddAvailableCatalog(const wxString& domain);
+
+    /**
+        Add a catalog for use with the current locale or fall back to the
+        original messages language.
+
+        This function behaves like AddAvailableCatalog() but also checks if the
+        strings used in the program, written in @a msgIdLanguage, can be used
+        without any translations on the current system and also returns @true
+        in this case, unlike AddAvailableCatalog().
+
         By default, i.e. if @a msgIdLanguage is not given, @c msgid strings are assumed
         to be in English and written only using 7-bit ASCII characters.
         If you have to deal with non-English strings or 8-bit characters in the
@@ -155,8 +196,10 @@ class wxTranslations
             code are used instead.
 
         @return
-            @true if catalog was successfully loaded, @false otherwise (which might
-            mean that the catalog is not found or that it isn't in the correct format).
+            @true if catalog was successfully loaded or loading it is
+            unnecessary because the original messages can be used directly,
+            @false otherwise (which might mean that the catalog is not found or
+            that it isn't in the correct format).
      */
     bool AddCatalog(const wxString& domain,
                     wxLanguage msgIdLanguage = wxLANGUAGE_ENGLISH_US);
@@ -167,7 +210,7 @@ class wxTranslations
         According to GNU gettext tradition, each catalog normally corresponds to
         'domain' which is more or less the application name.
 
-        @see AddCatalog()
+        @see AddAvailableCatalog()
      */
     bool IsLoaded(const wxString& domain) const;
 
@@ -302,7 +345,7 @@ class wxFileTranslationsLoader : public wxTranslationsLoader
         (in this order).
 
         This only applies to subsequent invocations of
-        wxTranslations::AddCatalog().
+        wxTranslations::AddAvailableCatalog().
     */
     static void AddCatalogLookupPathPrefix(const wxString& prefix);
 };
@@ -312,8 +355,7 @@ class wxFileTranslationsLoader : public wxTranslationsLoader
     resources.
 
     If you wish to store translation MO files in resources, you have to
-    enable this loader before calling wxTranslations::AddCatalog() or
-    wxLocale::AddCatalog():
+    enable this loader before calling wxTranslations::AddAvailableCatalog():
 
     @code
     wxTranslations::Get()->SetLoader(new wxResourceTranslationsLoader);

src/common/translation.cpp

@@ -1316,7 +1316,7 @@ bool wxTranslations::AddStdCatalog()
     // the name without the version if it's not found, as message catalogs
     // typically won't have the version in their names under non-Unix platforms
     // (i.e. where they're not installed by our own "make install").
-    if ( AddCatalog("wxstd-" wxSTRINGIZE(wxMAJOR_VERSION) "." wxSTRINGIZE(wxMINOR_VERSION)) )
+    if ( AddAvailableCatalog("wxstd-" wxSTRINGIZE(wxMAJOR_VERSION) "." wxSTRINGIZE(wxMINOR_VERSION)) )
         return true;
 
     if ( AddCatalog(wxS("wxstd")) )
@@ -1325,12 +1325,9 @@ bool wxTranslations::AddStdCatalog()
     return false;
 }
 
-bool wxTranslations::AddCatalog(const wxString& domain,
-                                wxLanguage msgIdLanguage)
+bool wxTranslations::AddAvailableCatalog(const wxString& domain)
 {
-    const wxString msgIdLang = wxUILocale::GetLanguageCanonicalName(msgIdLanguage);
-    const wxString domain_lang = GetBestTranslation(domain, msgIdLang);
-
+    const wxString domain_lang = GetBestAvailableTranslation(domain);
     if ( domain_lang.empty() )
     {
         wxLogTrace(TRACE_I18N,
@@ -1339,15 +1336,31 @@ bool wxTranslations::AddCatalog(const wxString& domain,
         return false;
     }
 
-    wxLogTrace(TRACE_I18N,
-                wxS("adding '%s' translation for domain '%s' (msgid language '%s')"),
-                domain_lang, domain, msgIdLang);
+    return LoadCatalog(domain, domain_lang);
+}
 
-    return LoadCatalog(domain, domain_lang, msgIdLang);
+bool wxTranslations::AddCatalog(const wxString& domain,
+                                wxLanguage msgIdLanguage)
+{
+    if ( AddAvailableCatalog(domain) )
+        return true;
+
+    const wxString msgIdLang = wxUILocale::GetLanguageCanonicalName(msgIdLanguage);
+    const wxString domain_lang = GetBestTranslation(domain, msgIdLang);
+
+    if ( msgIdLang == domain_lang )
+    {
+        wxLogTrace(TRACE_I18N,
+                    wxS("not using translations for domain '%s' with msgid language '%s'"),
+                    domain, msgIdLang);
+        return true;
+    }
+
+    return false;
 }
 
 
-bool wxTranslations::LoadCatalog(const wxString& domain, const wxString& lang, const wxString& msgIdLang)
+bool wxTranslations::LoadCatalog(const wxString& domain, const wxString& lang)
 {
     wxCHECK_MSG( m_loader, false, "loader can't be null" );
 
@@ -1384,15 +1397,6 @@ bool wxTranslations::LoadCatalog(const wxString& domain, const wxString& lang, c
             cat = m_loader->LoadCatalog(domain, baselang);
     }
 
-    if ( !cat )
-    {
-        // It is OK to not load catalog if the msgid language and m_language match,
-        // in which case we can directly display the texts embedded in program's
-        // source code:
-        if ( msgIdLang == lang )
-            return true;
-    }
-
     if ( cat )
     {
         // add it to the head of the list so that in GetString it will
@@ -1430,14 +1434,56 @@ wxString wxTranslations::GetBestTranslation(const wxString& domain,
 wxString wxTranslations::GetBestTranslation(const wxString& domain,
                                             const wxString& msgIdLanguage)
 {
-    // explicitly set language should always be respected
+    wxString lang = GetBestAvailableTranslation(domain);
+    if ( lang.empty() )
+    {
+        wxArrayString available;
+        available.push_back(msgIdLanguage);
+        available.push_back(msgIdLanguage.BeforeFirst('_'));
+        lang = GetPreferredUILanguage(available);
+        if ( lang.empty() )
+        {
+            wxLogTrace(TRACE_I18N,
+                       "no available language for domain '%s'", domain);
+        }
+        else
+        {
+            wxLogTrace(TRACE_I18N,
+                       "using message ID language '%s' for domain '%s'", lang);
+        }
+    }
+
+    return lang;
+}
+
+wxString wxTranslations::GetBestAvailableTranslation(const wxString& domain)
+{
+    const wxArrayString available(GetAvailableTranslations(domain));
     if ( !m_lang.empty() )
-        return m_lang;
+    {
+        wxLogTrace(TRACE_I18N,
+                   "searching for best translation to %s for domain '%s'",
+                   m_lang, domain);
+
+        wxString lang;
+        if ( available.Index(m_lang) != wxNOT_FOUND )
+        {
+            lang = m_lang;
+        }
+        else
+        {
+            const wxString baselang = m_lang.BeforeFirst('_');
+            if ( baselang != m_lang && available.Index(baselang) != wxNOT_FOUND )
+                lang = baselang;
+        }
 
-    wxArrayString available(GetAvailableTranslations(domain));
-    // it's OK to have duplicates, so just add msgid language
-    available.push_back(msgIdLanguage);
-    available.push_back(msgIdLanguage.BeforeFirst('_'));
+        if ( lang.empty() )
+            wxLogTrace(TRACE_I18N, " => no available translations found");
+        else
+            wxLogTrace(TRACE_I18N, " => found '%s'", lang);
+
+        return lang;
+    }
 
     wxLogTrace(TRACE_I18N, "choosing best language for domain '%s'", domain);
     LogTraceArray(" - available translations", available);

tests/intl/intltest.cpp

@@ -239,6 +239,39 @@ void IntlTestCase::IsAvailable()
     CPPUNIT_ASSERT_EQUAL( origLocale, setlocale(LC_ALL, nullptr) );
 }
 
+TEST_CASE("wxTranslations::Available", "[translations]")
+{
+    // We currently have translations for French and Japanese in this test
+    // directory, check that loading those succeeds but loading others doesn't.
+    wxFileTranslationsLoader::AddCatalogLookupPathPrefix("./intl");
+
+    const wxString domain("internat");
+
+    wxTranslations trans;
+
+    SECTION("All")
+    {
+        auto available = trans.GetAvailableTranslations(domain);
+        REQUIRE( available.size() == 2 );
+
+        available.Sort();
+        CHECK( available[0] == "fr" );
+        CHECK( available[1] == "ja" );
+    }
+
+    SECTION("French")
+    {
+        trans.SetLanguage(wxLANGUAGE_FRENCH);
+        CHECK( trans.AddAvailableCatalog(domain) );
+    }
+
+    SECTION("Italian")
+    {
+        trans.SetLanguage(wxLANGUAGE_ITALIAN);
+        CHECK_FALSE( trans.AddAvailableCatalog(domain) );
+    }
+}
+
 TEST_CASE("wxLocale::Default", "[locale]")
 {
     const int langDef = wxUILocale::GetSystemLanguage();