i18n: Add support for translating the class reference

- Parse `.po` files from `doc/translations/*.po` like already done
  with `editor/translations/*.po`.
- Add logic to register a doc translation mapping in `TranslationServer`
  and `EditorSettings`.
- Add `DTR()` to lookup the doc translation mapping (similar to `TTR()`).
  Strings are automatically dedented and stripped of whitespace to ensure
  that they would match the translation catalog.
- Use `DTR()` to translate relevant strings in `EditorHelp`,
  `EditorInspector`, `CreateDialog`, `ConnectionsDialog`.
- Small simplification to `TranslationLoaderPO`, the path argument was
  not really meaningful.

6 files changed, 41 insertions, 22 deletions

diff --git a/core/io/translation_loader_po.cpp b/core/io/translation_loader_po.cpp
index 4051bf2947..f1d3f19b58 100644
--- a/core/io/translation_loader_po.cpp
+++ b/core/io/translation_loader_po.cpp
@@ -33,7 +33,7 @@
 #include "core/os/file_access.h"
 #include "core/translation.h"
 
-RES TranslationLoaderPO::load_translation(FileAccess *f, Error *r_error, const String &p_path) {
+RES TranslationLoaderPO::load_translation(FileAccess *f, Error *r_error) {
 
 	enum Status {
 
@@ -67,7 +67,7 @@ RES TranslationLoaderPO::load_translation(FileAccess *f, Error *r_error, const S
 
 			if (status == STATUS_READING_ID) {
 				memdelete(f);
-				ERR_FAIL_V_MSG(RES(), p_path + ":" + itos(line) + " Unexpected EOF while reading 'msgid' at file: ");
+				ERR_FAIL_V_MSG(RES(), f->get_path() + ":" + itos(line) + " Unexpected EOF while reading 'msgid' at file: ");
 			} else {
 				break;
 			}
@@ -78,7 +78,7 @@ RES TranslationLoaderPO::load_translation(FileAccess *f, Error *r_error, const S
 			if (status == STATUS_READING_ID) {
 
 				memdelete(f);
-				ERR_FAIL_V_MSG(RES(), p_path + ":" + itos(line) + " Unexpected 'msgid', was expecting 'msgstr' while parsing: ");
+				ERR_FAIL_V_MSG(RES(), f->get_path() + ":" + itos(line) + " Unexpected 'msgid', was expecting 'msgstr' while parsing: ");
 			}
 
 			if (msg_id != "") {
@@ -100,7 +100,7 @@ RES TranslationLoaderPO::load_translation(FileAccess *f, Error *r_error, const S
 			if (status != STATUS_READING_ID) {
 
 				memdelete(f);
-				ERR_FAIL_V_MSG(RES(), p_path + ":" + itos(line) + " Unexpected 'msgstr', was expecting 'msgid' while parsing: ");
+				ERR_FAIL_V_MSG(RES(), f->get_path() + ":" + itos(line) + " Unexpected 'msgstr', was expecting 'msgid' while parsing: ");
 			}
 
 			l = l.substr(6, l.length()).strip_edges();
@@ -115,7 +115,7 @@ RES TranslationLoaderPO::load_translation(FileAccess *f, Error *r_error, const S
 			continue; //nothing to read or comment
 		}
 
-		ERR_FAIL_COND_V_MSG(!l.begins_with("\"") || status == STATUS_NONE, RES(), p_path + ":" + itos(line) + " Invalid line '" + l + "' while parsing: ");
+		ERR_FAIL_COND_V_MSG(!l.begins_with("\"") || status == STATUS_NONE, RES(), f->get_path() + ":" + itos(line) + " Invalid line '" + l + "' while parsing: ");
 
 		l = l.substr(1, l.length());
 		//find final quote
@@ -128,7 +128,7 @@ RES TranslationLoaderPO::load_translation(FileAccess *f, Error *r_error, const S
 			}
 		}
 
-		ERR_FAIL_COND_V_MSG(end_pos == -1, RES(), p_path + ":" + itos(line) + " Expected '\"' at end of message while parsing file: ");
+		ERR_FAIL_COND_V_MSG(end_pos == -1, RES(), f->get_path() + ":" + itos(line) + " Expected '\"' at end of message while parsing file: ");
 
 		l = l.substr(0, end_pos);
 		l = l.c_unescape();
@@ -153,7 +153,7 @@ RES TranslationLoaderPO::load_translation(FileAccess *f, Error *r_error, const S
 			config = msg_str;
 	}
 
-	ERR_FAIL_COND_V_MSG(config == "", RES(), "No config found in file: " + p_path + ".");
+	ERR_FAIL_COND_V_MSG(config == "", RES(), "No config found in file: " + f->get_path() + ".");
 
 	Vector<String> configs = config.split("\n");
 	for (int i = 0; i < configs.size(); i++) {
diff --git a/core/io/translation_loader_po.h b/core/io/translation_loader_po.h
index fe3a75e5eb..d280729e94 100644
--- a/core/io/translation_loader_po.h
+++ b/core/io/translation_loader_po.h
@@ -37,7 +37,7 @@
 
 class TranslationLoaderPO : public ResourceFormatLoader {
 public:
-	static RES load_translation(FileAccess *f, Error *r_error, const String &p_path = String());
+	static RES load_translation(FileAccess *f, Error *r_error = NULL);
 	virtual RES load(const String &p_path, const String &p_original_path = "", Error *r_error = NULL, bool p_use_sub_threads = false, float *r_progress = nullptr);
 	virtual void get_recognized_extensions(List<String> *p_extensions) const;
 	virtual bool handles_type(const String &p_type) const;
diff --git a/core/translation.cpp b/core/translation.cpp
index 7399fa5619..df3661e5d0 100644
--- a/core/translation.cpp
+++ b/core/translation.cpp
@@ -1176,7 +1176,6 @@ void TranslationServer::setup() {
 		set_locale(OS::get_singleton()->get_locale());
 	fallback = GLOBAL_DEF("locale/fallback", "en");
 #ifdef TOOLS_ENABLED
-
 	{
 		String options = "";
 		int idx = 0;
@@ -1189,7 +1188,6 @@ void TranslationServer::setup() {
 		ProjectSettings::get_singleton()->set_custom_property_info("locale/fallback", PropertyInfo(Variant::STRING, "locale/fallback", PROPERTY_HINT_ENUM, options));
 	}
 #endif
-	//load translations
 }
 
 void TranslationServer::set_tool_translation(const Ref<Translation> &p_translation) {
@@ -1197,15 +1195,26 @@ void TranslationServer::set_tool_translation(const Ref<Translation> &p_translati
 }
 
 StringName TranslationServer::tool_translate(const StringName &p_message) const {
-
 	if (tool_translation.is_valid()) {
 		StringName r = tool_translation->get_message(p_message);
-
 		if (r) {
 			return r;
 		}
 	}
+	return p_message;
+}
 
+void TranslationServer::set_doc_translation(const Ref<Translation> &p_translation) {
+	doc_translation = p_translation;
+}
+
+StringName TranslationServer::doc_translate(const StringName &p_message) const {
+	if (doc_translation.is_valid()) {
+		StringName r = doc_translation->get_message(p_message);
+		if (r) {
+			return r;
+		}
+	}
 	return p_message;
 }
 
diff --git a/core/translation.h b/core/translation.h
index b9e07fa2b1..29a068f450 100644
--- a/core/translation.h
+++ b/core/translation.h
@@ -73,6 +73,7 @@ class TranslationServer : public Object {
 
 	Set<Ref<Translation>> translations;
 	Ref<Translation> tool_translation;
+	Ref<Translation> doc_translation;
 
 	Map<String, String> locale_name_map;
 
@@ -109,6 +110,8 @@ public:
 
 	void set_tool_translation(const Ref<Translation> &p_translation);
 	StringName tool_translate(const StringName &p_message) const;
+	void set_doc_translation(const Ref<Translation> &p_translation);
+	StringName doc_translate(const StringName &p_message) const;
 
 	void setup();
 
diff --git a/core/ustring.cpp b/core/ustring.cpp
index da089dce40..8027ae29b5 100644
--- a/core/ustring.cpp
+++ b/core/ustring.cpp
@@ -4412,7 +4412,6 @@ String String::unquote() const {
 
 #ifdef TOOLS_ENABLED
 String TTR(const String &p_text) {
-
 	if (TranslationServer::get_singleton()) {
 		return TranslationServer::get_singleton()->tool_translate(p_text);
 	}
@@ -4420,10 +4419,18 @@ String TTR(const String &p_text) {
 	return p_text;
 }
 
+String DTR(const String &p_text) {
+	if (TranslationServer::get_singleton()) {
+		// Comes straight from the XML, so remove indentation and any trailing whitespace.
+		const String text = p_text.dedent().strip_edges();
+		return TranslationServer::get_singleton()->doc_translate(text);
+	}
+
+	return p_text;
+}
 #endif
 
 String RTR(const String &p_text) {
-
 	if (TranslationServer::get_singleton()) {
 		String rtr = TranslationServer::get_singleton()->tool_translate(p_text);
 		if (rtr == String() || rtr == p_text) {
diff --git a/core/ustring.h b/core/ustring.h
index e70b2bfe27..33320a0a49 100644
--- a/core/ustring.h
+++ b/core/ustring.h
@@ -415,25 +415,25 @@ _FORCE_INLINE_ bool is_str_less(const L *l_ptr, const R *r_ptr) {
 
 /* end of namespace */
 
-//tool translate
+// Tool translate (TTR and variants) for the editor UI,
+// and doc translate for the class reference (DTR).
 #ifdef TOOLS_ENABLED
-
-//gets parsed
+// Gets parsed.
 String TTR(const String &);
-//use for C strings
+String DTR(const String &);
+// Use for C strings.
 #define TTRC(m_value) (m_value)
-//use to avoid parsing (for use later with C strings)
+// Use to avoid parsing (for use later with C strings).
 #define TTRGET(m_value) TTR(m_value)
 
 #else
-
 #define TTR(m_value) (String())
+#define DTR(m_value) (String())
 #define TTRC(m_value) (m_value)
 #define TTRGET(m_value) (m_value)
-
 #endif
 
-//tool or regular translate
+// Runtime translate for the public node API.
 String RTR(const String &);
 
 bool is_symbol(CharType c);