Common: Assert that translatable strings use positional arguments

Like PR 9260, but for a different requirement (see PR 9253).

Source/Core/Common/FormatUtil.h

@@ -38,4 +38,39 @@ constexpr std::size_t CountFmtReplacementFields(std::string_view s)
 static_assert(CountFmtReplacementFields("") == 0);
 static_assert(CountFmtReplacementFields("{} test {:x}") == 2);
 static_assert(CountFmtReplacementFields("{} {{}} test {{{}}}") == 2);
+
+constexpr bool ContainsNonPositionalArguments(std::string_view s)
+{
+  for (std::size_t i = 0; i < s.size(); ++i)
+  {
+    if (s[i] != '{' || i + 1 == s.size())
+      continue;
+
+    const char next = s[i + 1];
+
+    // If the opening brace is followed by another brace, what we have is
+    // an escaped brace, not a replacement field.
+    if (next == '{')
+    {
+      // Skip the second brace.
+      // This ensures that e.g. {{{}}} is counted correctly: when the first brace character
+      // is read and detected as being part of an '{{' escape sequence, the second character
+      // is skipped so the most inner brace (the third character) is not detected
+      // as the end of an '{{' pair.
+      ++i;
+    }
+    else if (next == '}' || next == ':')
+    {
+      return true;
+    }
+  }
+  return false;
+}
+
+static_assert(!ContainsNonPositionalArguments(""));
+static_assert(ContainsNonPositionalArguments("{}"));
+static_assert(!ContainsNonPositionalArguments("{0}"));
+static_assert(ContainsNonPositionalArguments("{:x}"));
+static_assert(!ContainsNonPositionalArguments("{0:x}"));
+static_assert(!ContainsNonPositionalArguments("{0} {{}} test {{{1}}}"));
 }  // namespace Common

Source/Core/Common/MsgHandler.h

@@ -102,6 +102,16 @@ std::string FmtFormatT(const char* string, Args&&... args)
                                                     ##__VA_ARGS__);                                \
   }()
 
+#define GenericAlertFmtT(yes_no, style, format, ...)                                               \
+  [&] {                                                                                            \
+    static_assert(!Common::ContainsNonPositionalArguments(format),                                 \
+                  "Translatable strings must use positional arguments (e.g. {0} instead of {})");  \
+    /* Use a macro-like name to avoid shadowing warnings */                                        \
+    constexpr auto GENERIC_ALERT_FMT_N = Common::CountFmtReplacementFields(format);                \
+    return Common::MsgAlertFmt<GENERIC_ALERT_FMT_N>(yes_no, style, FMT_STRING(format),             \
+                                                    ##__VA_ARGS__);                                \
+  }()
+
 #define SuccessAlertFmt(format, ...)                                                               \
   GenericAlertFmt(false, Common::MsgType::Information, format, ##__VA_ARGS__)
 
@@ -119,16 +129,16 @@ std::string FmtFormatT(const char* string, Args&&... args)
 
 // Use these macros (that do the same thing) if the message should be translated.
 #define SuccessAlertFmtT(format, ...)                                                              \
-  GenericAlertFmt(false, Common::MsgType::Information, format, ##__VA_ARGS__)
+  GenericAlertFmtT(false, Common::MsgType::Information, format, ##__VA_ARGS__)
 
 #define PanicAlertFmtT(format, ...)                                                                \
-  GenericAlertFmt(false, Common::MsgType::Warning, format, ##__VA_ARGS__)
+  GenericAlertFmtT(false, Common::MsgType::Warning, format, ##__VA_ARGS__)
 
 #define PanicYesNoFmtT(format, ...)                                                                \
-  GenericAlertFmt(true, Common::MsgType::Warning, format, ##__VA_ARGS__)
+  GenericAlertFmtT(true, Common::MsgType::Warning, format, ##__VA_ARGS__)
 
 #define AskYesNoFmtT(format, ...)                                                                  \
-  GenericAlertFmt(true, Common::MsgType::Question, format, ##__VA_ARGS__)
+  GenericAlertFmtT(true, Common::MsgType::Question, format, ##__VA_ARGS__)
 
 #define CriticalAlertFmtT(format, ...)                                                             \
-  GenericAlertFmt(false, Common::MsgType::Critical, format, ##__VA_ARGS__)
+  GenericAlertFmtT(false, Common::MsgType::Critical, format, ##__VA_ARGS__)