feat: add -input= option to set initial prompt value

[lambdalisue]

Summary

Adds support for the -input= option to pre-fill the picker's prompt with an initial query value.

Changes

• New utility module: denops/fall/util/args.ts

  • parseArgs(): Parse command-line arguments with quote and escape support
  • extractOption(): Extract option arguments by prefix
  • Comprehensive tests (20 test cases)

• Updated picker:command handler: denops/fall/main/picker.ts

  • Extract -input= option from arguments before source name
  • Create initial PickerContext with query when specified
  • Options after source name are treated as source arguments

• Command syntax change: plugin/fall.vim

  • Use <q-args> instead of <f-args> to support quoted arguments

• Documentation: doc/fall.txt

  • Updated command syntax: :Fall [-input={value}] {source} [{cmdarg}...]
  • Added usage examples and constraints
  • Clarified that -input= must appear before source name

Usage Examples

" Set initial prompt value
:Fall -input="Hello world" file

" Combine with source arguments
:Fall -input="search term" grep /path/to/dir

" Invalid: option after source (treated as source argument)
:Fall file -input="test"

Test Coverage

• 15 unit tests for parseArgs() and extractOption()
• 5 integration tests for picker:command specification
• All tests passing ✅
• Type checks passing ✅

Breaking Changes

None. This is a backward-compatible feature addition.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.84%. Comparing base (abf9c78) to head (cdb92c5).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #45      +/-   ##
==========================================
+ Coverage   83.45%   83.84%   +0.38%     
==========================================
  Files          31       32       +1     
  Lines        1977     2024      +47     
  Branches      200      214      +14     
==========================================
+ Hits         1650     1697      +47     
  Misses        324      324              
  Partials        3        3              

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