typos/docs/design.md

Design

Requirements

Spell checks source code:

• Requires special word-splitting logic to handle situations like hex (0xDEADBEEF), c\nescapes, snake_case, CamelCase, SCREAMING_CASE, and maybe arrow-case.
• Each programming language has its own quirks, like abbreviations, lack of word separator (copysign), etc
• Backwards compatibility might require keeping misspelled words.
• Case for proper nouns is irrelevant.

Checking for errors in a CI:

• No false-positives.
• On spelling errors, sets the exit code to fail the CI.
• Machine-independent, repo-specific configuration
  • As compared to layered config with the users system or the command-line

Quick feedback and resolution for developer:

• Fix errors for the user.
• Integration into other programs, like editors:
  • fork: easy to call into and provides a stable API, including output format
  • linking: either in the language of choice or bindings can be made to language of choice.

Trade Offs

Corrections vs Dictionaries

Corrections: Known misspellings that map to their corresponding dictionary word

• Ignores unknown typos
• Ignores typos that follow c-escapes if they aren't handled correctly
• Good for unassisted automated correcting
• Fast, can quickly run across large code bases

Dictionary: A confidence rating is given for how close a word is to one in a dictionary

• Sensitive to false positives due to hex numbers and c-escapes
• Used in word processors and other traditional spell checking applications
• Good when there is a UI to let the user know and override any decisions

Identifiers and Words

With a focus on spell checking source code, most text will be in the form of identifiers that are made up of words conjoined via snake_case, CamelCase, etc. A typo at the word level might not be a typo as part of an identifier, so identifiers get checked and, if not in a dictionary, will then be split into words to be checked.

Identifiers are defined using unicode's XID_Continue which includes [a-zA-Z0-9_].

Words are split from identifiers on case changes as well as breaks in [a-zA-Z] with a special case to handle acronyms. For example, First10HTMLTokens would be split as first, html, tokens.

To see this in action, run typos --identifiers or typos --words.