[fp-enhancer] Improve pkg/cli: pre-allocate slices with known capacity

[github-actions]

Functional/Immutability Enhancements - Package: pkg/cli

Applies pre-allocation improvements to 13 files in pkg/cli, replacing bare var result []string declarations with make([]string, 0, len(lines)) in functions that process YAML frontmatter line slices.

Round-Robin Progress: First run, processing pkg/cli. Next package to process: pkg/console

Summary of Changes

Immutability / Initialization Improvements

All 13 changed files follow the same pattern: a function receives a []string slice (typically named lines, lockFiles, or a map), builds a result slice by appending, and returns it. The original var result []string declaration causes the runtime to start with a nil slice and grow it on every append, reallocating 2× each time. By using make([]string, 0, len(input)) we declare the upper-bound capacity upfront, eliminating redundant allocations for typical-size inputs.

Codemod line-transform functions — output is always ≤ input length:

• codemod_bash_anonymous.go — replaceBashAnonymousWithTrue
• codemod_discussion_flag.go — anonymous transform closure
• codemod_expires_integer.go — convertExpiresIntegersToDayStrings
• codemod_github_app.go — renameAppToGitHubApp
• codemod_mcp_mode_to_type.go — renameModeToTypeInMCPServers
• codemod_mcp_network.go — removeFieldFromMCPServer, updateNetworkAllowed, addAllowedToNetwork
• codemod_playwright_domains.go — removeFieldFromPlaywright
• codemod_safe_inputs_to_mcp_scripts.go — renameTopLevelKey
• codemod_serena_local_mode.go — replaceSerenaLocalModeWithDocker
• codemod_yaml_utils.go — removeFieldFromBlock

Other pre-allocations:

• actionlint.go — relPaths slice pre-allocated to len(lockFiles) (exact match)
• add_interactive_engine.go — engineOptions slice pre-allocated to len(catalog.All())
• run_interactive.go — result slice pre-allocated to len(inputPtrs)

Benefits

• Performance: Reduces GC pressure; avoids repeated slice growth for inputs of typical size
• Clarity: Declarative capacity hint communicates the expected output size at a glance
• Consistency: All line-transform functions in the codemod subsystem now use the same pattern

Principles Applied

1. Immutability First: No var x []T when size is known
2. Declarative Over Imperative: Initialization expresses expected capacity
3. Pragmatic Balance: Only applied where size bound is clearly available; no speculative changes

Testing

• ✅ All existing tests pass — verified with targeted test runs covering every changed file
• ✅ go build ./pkg/cli/ succeeds
• ✅ go vet ./pkg/cli/ passes
• ✅ No behavioral changes — only allocation strategy changed
• ✅ Test files verified present before refactoring (all 13 files have corresponding _test.go)

Before / After Example

// Before
func replaceSerenaLocalModeWithDocker(lines []string) ([]string, bool) {
    var result []string
    // ...appends grow slice from nil repeatedly
}

// After
func replaceSerenaLocalModeWithDocker(lines []string) ([]string, bool) {
    result := make([]string, 0, len(lines))
    // ...appends never reallocate for typical inputs
}

Generated by Functional Pragmatist · ◷

• expires on Mar 20, 2026, 9:25 AM UTC

[pelikhan]

/q turn off this optimization, it generates codeql violations

[github-actions]

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