Fix: Infinite recursion crash in wikitext parser

[sayeedjoy]

Problem

The app kept crashing with a StackOverflowError on some Wikipedia pages because the toWikitextAnnotatedString function was getting stuck in an endless loop. Certain templates like {{small}} were sending the same wikitext back into the parser again and again, which caused the function to call itself repeatedly until the app crashed.

Stack Trace Sample

 at org.nsh07.wikireader.parser.WikitextToAnnotatedStringKt.toWikitextAnnotatedString(wikitextToAnnotatedString.kt:592)
  at org.nsh07.wikireader.parser.WikitextToAnnotatedStringKt$$ExternalSyntheticLambda1.invoke(D8$$SyntheticClass:0)
  at org.nsh07.wikireader.parser.WikitextToAnnotatedStringKt.toWikitextAnnotatedString(wikitextToAnnotatedString.kt:592)
  at org.nsh07.wikireader.parser.WikitextToAnnotatedStringKt$$ExternalSyntheticLambda1.invoke(D8$$SyntheticClass:0)

Solution

Implemented a two-part fix:

1. Recursion Depth Guard

• Added a thread-local recursion counter with a maximum depth of 64 nested parsing calls
• When the limit is reached, the parser returns plain text (AnnotatedString(this)) instead of crashing
• The guard uses a try/finally block to ensure proper cleanup of the recursion counter

2. Template Branch Hardening

• Fixed multiple template handlers that could cause infinite recursion when used without parameters
• Changed substringAfter('|') to substringAfter('|', "") for templates like:
  • {{abbr}}, {{efn}}, {{val}}, {{var}}, {{small}} family, {{dfn}}, {{US$}}, {{hatnote}}, {{rp}}, {{isbn}}, {{sfrac}}, {{unichar}}, {{char}}, {{noflag}}, {{nowrap}} family, {{url}}, {{format price}}, {{transliteration}}
• This ensures that when a template has no | parameter, the parser receives an empty string instead of the full template text, preventing self-recursion

Changes

• File: app/src/main/java/org/nsh07/wikireader/parser/wikitextToAnnotatedString.kt
  • Added MAX_WIKITEXT_RECURSION_DEPTH constant (64)
  • Added WikitextParserState object with thread-local recursion counter
  • Added recursion guard at the start of toWikitextAnnotatedString function
  • Hardened 20+ template branches to prevent infinite recursion

Testing

• Verified no compilation errors
• Test on previously crashing Wikipedia pages
• Verify normal content (links, headings, references, templates) still renders correctly
• Confirm app no longer crashes with StackOverflowError

Notes

• In extreme edge cases with deeply nested or malformed templates, the parser may display raw wikitext instead of fully parsed content. This is intentional to prevent crashes.
• The recursion limit of 64 should be sufficient for all legitimate Wikipedia content while preventing runaway recursion.

[Copilot]

Pull request overview

This PR fixes a critical infinite recursion bug in the wikitext parser that was causing StackOverflowError crashes when parsing certain Wikipedia templates. The solution implements a two-pronged approach: a recursion depth guard and hardening of template parameter extraction.

Key changes:

• Added a ThreadLocal recursion depth counter with a maximum depth of 64 to gracefully handle deeply nested or malformed wikitext
• Fixed 18+ template handlers to use substringAfter('|', "") with an empty string default, preventing self-recursion when templates lack parameters

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[nsh07]

Looks good to me. Can you please fix the changes Copilot has suggested? Otherwise it's good.

[sayeedjoy]

Looks good to me. Can you please fix the changes Copilot has suggested? Otherwise it's good.

Copilot suggestions accepted.