AK: Make StringBuilder::try_append_code_point actually fallible

It currently uses the non-fallible `append` method to append each UTF-8
encoded byte of the code point.

1 files changed, 30 insertions, 0 deletions

diff --git a/AK/UnicodeUtils.h b/AK/UnicodeUtils.h
index c0e2a13ad2..fd55dd611d 100644
--- a/AK/UnicodeUtils.h
+++ b/AK/UnicodeUtils.h
@@ -6,6 +6,8 @@
 
 #pragma once
 
+#include <AK/Concepts.h>
+#include <AK/Error.h>
 #include <AK/Forward.h>
 
 namespace AK::UnicodeUtils {
@@ -35,4 +37,32 @@ template<typename Callback>
     return -1;
 }
 
+template<FallibleFunction<char> Callback>
+[[nodiscard]] ErrorOr<int> try_code_point_to_utf8(u32 code_point, Callback&& callback)
+{
+    if (code_point <= 0x7f) {
+        TRY(callback(static_cast<char>(code_point)));
+        return 1;
+    }
+    if (code_point <= 0x07ff) {
+        TRY(callback(static_cast<char>((((code_point >> 6) & 0x1f) | 0xc0))));
+        TRY(callback(static_cast<char>((((code_point >> 0) & 0x3f) | 0x80))));
+        return 2;
+    }
+    if (code_point <= 0xffff) {
+        TRY(callback(static_cast<char>((((code_point >> 12) & 0x0f) | 0xe0))));
+        TRY(callback(static_cast<char>((((code_point >> 6) & 0x3f) | 0x80))));
+        TRY(callback(static_cast<char>((((code_point >> 0) & 0x3f) | 0x80))));
+        return 3;
+    }
+    if (code_point <= 0x10ffff) {
+        TRY(callback(static_cast<char>((((code_point >> 18) & 0x07) | 0xf0))));
+        TRY(callback(static_cast<char>((((code_point >> 12) & 0x3f) | 0x80))));
+        TRY(callback(static_cast<char>((((code_point >> 6) & 0x3f) | 0x80))));
+        TRY(callback(static_cast<char>((((code_point >> 0) & 0x3f) | 0x80))));
+        return 4;
+    }
+    return -1;
+}
+
 }