Add lookup table lint analyzer

[Peyton-Spencer]

Summary

• add lookuptablelint, a go/analysis analyzer for small static lookup maps
• report map[k]bool / map[k]struct{} lookup tables that should be predicate helpers with single-case switches
• ship a standalone lookuptablelint singlechecker command and analysistest coverage

Notes

• no suggested fix is emitted because rewriting call sites from map lookups to predicate calls is intentionally more invasive
• default reporting is capped at 64 entries via -max_entries; local benchmarks showed switches faster through thousands of same-length string cases, but 64 keeps the lint focused on obvious lookup tables

Validation

• PATH=/opt/homebrew/bin:$PATH ./scripts/test-all.sh

Summary by CodeRabbit

• New Features

  • Added a new Go analysis check that flags small static lookup maps and suggests using predicate-style helpers.
  • Added a command-line entrypoint so the analyzer can be run directly.
  • Added test coverage and sample cases for supported and unsupported lookup patterns.

• Documentation

  • Added package documentation describing what the analyzer reports.

• Chores

  • Updated the Go toolchain and related module dependencies.

[coderabbitai]

📝 Walkthrough

Walkthrough

Adds a new Go static analysis pass lookuptablelint that detects small compile-time lookup maps (bool or empty-struct valued) and suggests predicate helpers, including its CLI entrypoint, documentation, module configuration, tests, and testdata fixtures.

Changes

Lookup Table Lint Analyzer

Layer / File(s)	Summary
Analyzer registration and configuration lookuptablelint/analyzer.go	Declares Analyzer metadata, a configurable -max_entries flag, and internal candidate/kind data model for tracking bool vs struct lookup tables.
Candidate discovery and classification lookuptablelint/analyzer.go	Implements the run control flow, walks var declarations to find map-literal candidates, and classifies them by switchable key type, bool/empty-struct element type, and entry-count bounds with compile-time constant checks.
Usage safety analysis lookuptablelint/analyzer.go	Scans identifier usages via a parent-pointer AST map to distinguish safe read-only index lookups from writes/mutations, requiring two-value lookup shape for struct tables.
Type predicates, constant validation, naming, and generated-code detection lookuptablelint/analyzer.go	Adds helpers for allowed key/value type checks, compile-time constant/value validation, predicate-name generation for diagnostic messages, and skipping generated files.
CLI entrypoint, package docs, and module config lookuptablelint/cmd/lookuptablelint/main.go, lookuptablelint/doc.go, lookuptablelint/go.mod	Wires Analyzer into singlechecker.Main, adds a package doc comment, and sets Go/toolchain versions with x/tools, x/mod, x/sync dependencies.
Analyzer tests and testdata fixtures lookuptablelint/analyzer_test.go, lookuptablelint/testdata/src/a/a.go	Adds TestAnalyzer using analysistest against testdata package "a", which defines bool/struct/int lookup tables, an exported map, and helper functions exercising read, mutate, range, and length usage patterns.

Estimated code review effort: 4 (Complex) | ~60 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the main change: adding a lookup table lint analyzer.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch codex/lookuptablelint

Warning

There were issues while running some tools. Please review the errors and either fix the tool's configuration or disable the tool if it's a critical failure.

🔧 golangci-lint (2.12.2)

level=error msg="[linters_context] typechecking error: pattern ./...: directory prefix . does not contain modules listed in go.work or their selected dependencies"

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[coderabbitai]

🧹 Nitpick comments (2)

lookuptablelint/testdata/src/a/a.go (1)

56-126: 📐 Maintainability & Code Quality | 🔵 Trivial | ⚡ Quick win

Add a boundary test for exactly 64 entries.

tooLarge has 65 entries (000–064), which correctly exceeds the default -max_entries=64. However, there's no positive test for a map with exactly 64 entries. If the boundary comparison accidentally changes from <= to <, no test would catch the regression.

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@lookuptablelint/testdata/src/a/a.go` around lines 56 - 126, Add a boundary
test in the lookuptablelint testdata around the tooLarge/tooSmall maps to cover
a map with exactly 64 entries and verify it is accepted; this will protect the
max_entries check from regressing from <= to <. Use the existing tooLarge
fixture in a.go as the location to derive a 64-entry case, and ensure the test
clearly exercises the lookup-table limit boundary.

lookuptablelint/analyzer.go (1)

302-313: 📐 Maintainability & Code Quality | 🔵 Trivial | ⚡ Quick win

Use ast.IsGenerated(file) here. The standard helper matches the generated-code convention directly and avoids the loose substring scan. Remove the now-unused strings import too.

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@lookuptablelint/analyzer.go` around lines 302 - 313, Replace the custom
generated-code detection in generated(file *ast.File) with the standard
ast.IsGenerated(file) helper so the analyzer uses the official convention
instead of scanning comments manually. After switching, remove the now-unused
strings import from analyzer.go and make sure any remaining references to the
old substring check are eliminated.

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Nitpick comments:
In `@lookuptablelint/analyzer.go`:
- Around line 302-313: Replace the custom generated-code detection in
generated(file *ast.File) with the standard ast.IsGenerated(file) helper so the
analyzer uses the official convention instead of scanning comments manually.
After switching, remove the now-unused strings import from analyzer.go and make
sure any remaining references to the old substring check are eliminated.

In `@lookuptablelint/testdata/src/a/a.go`:
- Around line 56-126: Add a boundary test in the lookuptablelint testdata around
the tooLarge/tooSmall maps to cover a map with exactly 64 entries and verify it
is accepted; this will protect the max_entries check from regressing from <= to
<. Use the existing tooLarge fixture in a.go as the location to derive a
64-entry case, and ensure the test clearly exercises the lookup-table limit
boundary.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: b737526b-b0ab-43f4-acc5-89cf155d0416

📥 Commits

Reviewing files that changed from the base of the PR and between 1e60c7c and 40e9af4.

⛔ Files ignored due to path filters (2)

• go.work is excluded by !**/*.work
• lookuptablelint/go.sum is excluded by !**/*.sum

📒 Files selected for processing (6)

• lookuptablelint/analyzer.go
• lookuptablelint/analyzer_test.go
• lookuptablelint/cmd/lookuptablelint/main.go
• lookuptablelint/doc.go
• lookuptablelint/go.mod
• lookuptablelint/testdata/src/a/a.go