Merge #18922: gui: Do not translate InitWarning messages in debug.log

78be8d97d3 util: Drop OpOriginal() and OpTranslated() (Hennadii Stepanov)
da16f95c3f gui: Do not translate InitWarning messages in debug.log (Hennadii Stepanov)
4c9b9a4882 util: Enhance Join() (Hennadii Stepanov)
fe05dd0611 util: Enhance bilingual_str (Hennadii Stepanov)

Pull request description:

  This PR forces the `bitcoin-qt` to write `InitWarning()` messages to the `debug.log` file in untranslated form, i.e., in English.

  On master (376294cde6):
  ```
  $ ./src/qt/bitcoin-qt -lang=nl -debug=vladidation -printtoconsole | grep 'vladi'
  Warning: Niet-ondersteunde logcategorie -debug=vladidation.
  2020-05-09T12:39:59Z Warning: Niet-ondersteunde logcategorie -debug=vladidation.
  2020-05-09T12:40:02Z Command-line arg: debug="vladidation"
  ```

  With this PR:
  ```
  $ ./src/qt/bitcoin-qt -lang=nl -debug=vladidation -printtoconsole | grep 'vladi'
  Warning: Unsupported logging category -debug=vladidation.
  2020-05-09T12:42:04Z Warning: Unsupported logging category -debug=vladidation.
  2020-05-09T12:42:35Z Command-line arg: debug="vladidation"
  ```

  ![Screenshot from 2020-05-09 15-42-31](https://user-images.githubusercontent.com/32963518/81474073-c7a50e00-920b-11ea-8775-c41122dacafe.png)

  Related to #16218.

ACKs for top commit:
  laanwj:
    ACK 78be8d97d3
  jonasschnelli:
    utACK 78be8d97d3
  MarcoFalke:
    ACK 78be8d97d3 📢

Tree-SHA512: 48e9ecd23c4dd8ec262e3eb94f8e30944bcc9c6c163245fb837b2e0c484d4d0b4f47f7abc638c14edc27d635d340ba3ee4ba4506b062399e9cf59a1564c98755

src/util/string.h

@@ -30,10 +30,11 @@ NODISCARD inline std::string TrimString(const std::string& str, const std::strin
  * @param separator  The separator
  * @param unary_op   Apply this operator to each item in the list
  */
-template <typename T, typename UnaryOp>
-std::string Join(const std::vector<T>& list, const std::string& separator, UnaryOp unary_op)
+template <typename T, typename BaseType, typename UnaryOp>
+auto Join(const std::vector<T>& list, const BaseType& separator, UnaryOp unary_op)
+    -> decltype(unary_op(list.at(0)))
 {
-    std::string ret;
+    decltype(unary_op(list.at(0))) ret;
     for (size_t i = 0; i < list.size(); ++i) {
         if (i > 0) ret += separator;
         ret += unary_op(list.at(i));
@@ -41,9 +42,16 @@ std::string Join(const std::vector<T>& list, const std::string& separator, Unary
     return ret;
 }
 
+template <typename T>
+T Join(const std::vector<T>& list, const T& separator)
+{
+    return Join(list, separator, [](const T& i) { return i; });
+}
+
+// Explicit overload needed for c_str arguments, which would otherwise cause a substitution failure in the template above.
 inline std::string Join(const std::vector<std::string>& list, const std::string& separator)
 {
-    return Join(list, separator, [](const std::string& i) { return i; });
+    return Join<std::string>(list, separator);
 }
 
 /**

src/util/translation.h

@@ -16,21 +16,23 @@
 struct bilingual_str {
     std::string original;
     std::string translated;
+
+    bilingual_str& operator+=(const bilingual_str& rhs)
+    {
+        original += rhs.original;
+        translated += rhs.translated;
+        return *this;
+    }
 };
 
-inline bilingual_str operator+(const bilingual_str& lhs, const bilingual_str& rhs)
+inline bilingual_str operator+(bilingual_str lhs, const bilingual_str& rhs)
 {
-    return bilingual_str{
-        lhs.original + rhs.original,
-        lhs.translated + rhs.translated};
+    lhs += rhs;
+    return lhs;
 }
 
 /** Mark a bilingual_str as untranslated */
 inline bilingual_str Untranslated(std::string original) { return {original, original}; }
-/** Unary operator to return the original */
-inline std::string OpOriginal(const bilingual_str& b) { return b.original; }
-/** Unary operator to return the translation */
-inline std::string OpTranslated(const bilingual_str& b) { return b.translated; }
 
 namespace tinyformat {
 template <typename... Args>