Bug 1650013 - Strip unexpected leading slash from absolute path on Windows when loading hyphenation resource. r=heycam

Differential Revision: https://phabricator.services.mozilla.com/D81980

intl/hyphenation/glue/nsHyphenator.cpp

@@ -179,8 +179,18 @@ nsHyphenator::nsHyphenator(nsIURI* aURI, bool aHyphenateCapitalized)
     // remains zero; mDict is not a pointer to the raw data but an opaque
     // reference to a Rust object, and can only be freed by passing it to
     // mapped_hyph_free_dictionary().
+    // (This case occurs in unpackaged developer builds.)
     nsAutoCString path;
     aURI->GetFilePath(path);
+#if XP_WIN
+    // GetFilePath returns the path with an unexpected leading slash (like
+    // "/c:/path/to/firefox/...") that may prevent it being found if it's an
+    // absolute Windows path starting with a drive letter.
+    // So check for this case and strip the slash.
+    if (path.Length() > 2 && path[0] == '/' && path[2] == ':') {
+      path.Cut(0, 1);
+    }
+#endif
     UniquePtr<const HyphDic> dic(mapped_hyph_load_dictionary(path.get()));
     if (dic) {
       mDict = AsVariant(std::move(dic));