feat(lang): add TypeScript checker

.github/workflows/ci.yml

@@ -21,6 +21,20 @@ jobs:
           go-version: '1.26.1'
           cache: true
 
+      # Node is required by the TS mutation evals (npm test -> vitest /
+      # node). Minimum 22.6 so `--experimental-strip-types` is default.
+      - uses: actions/setup-node@v4
+        with:
+          node-version: '22'
+
+      - name: Cache npm
+        uses: actions/cache@v4
+        with:
+          path: ~/.npm
+          key: npm-${{ runner.os }}-${{ hashFiles('**/package.json', '**/package-lock.json') }}
+          restore-keys: |
+            npm-${{ runner.os }}-
+
       - name: Build
         run: go build ./...
 
@@ -30,6 +44,11 @@ jobs:
       - name: Vet
         run: go vet ./...
 
+      - name: Eval — TypeScript (EVAL-3)
+        env:
+          CI: "true"
+        run: make eval-ts
+
   diffguard:
     # Dogfooding: run diffguard's own quality gate against this repo.
     # Mutation testing runs at 20% sample rate here as a fast smoke

Makefile

@@ -2,7 +2,12 @@ BINARY := diffguard
 PKG    := ./cmd/diffguard
 PATHS  := internal/,cmd/
 
-.PHONY: all build install test coverage check check-mutation check-fast clean help
+# Shared env for evaluation suites. CI=true nudges sub-commands (cargo,
+# npm) into non-interactive modes; CARGO_INCREMENTAL=0 keeps the
+# mutation runs deterministic and avoids a multi-GB incremental cache.
+EVAL_ENV := CI=true CARGO_INCREMENTAL=0
+
+.PHONY: all build install test coverage check check-mutation check-fast eval-ts clean help
 
 all: build
 
@@ -28,6 +33,9 @@ check: build ## Run the full quality gate including 100% mutation testing (slow)
 check-mutation: build ## Only the mutation section, full codebase
 	./$(BINARY) --paths $(PATHS) --fail-on warn .
 
+eval-ts: ## Run the TypeScript correctness eval (EVAL-3). Requires node+npm for mutation tests.
+	$(EVAL_ENV) go test ./internal/lang/tsanalyzer/... -run TestEval -count=1 -v
+
 clean: ## Remove build artifacts
 	rm -f $(BINARY) coverage.out
 

README.md

@@ -1,6 +1,6 @@
 # diffguard
 
-A targeted code quality gate for Go repositories. Analyzes either the changed regions of a git diff (CI mode) or specified files/directories (refactoring mode), and reports on complexity, size, dependency structure, churn risk, and mutation test coverage.
+A targeted code quality gate for Go and TypeScript repositories. Analyzes either the changed regions of a git diff (CI mode) or specified files/directories (refactoring mode), and reports on complexity, size, dependency structure, churn risk, and mutation test coverage.
 
 ## Why
 
@@ -42,6 +42,10 @@ diffguard --base main /path/to/repo
 diffguard --paths internal/foo/bar.go /path/to/repo
 diffguard --paths internal/foo/,internal/bar/ /path/to/repo
 
+# TypeScript project (vitest/jest auto-detected from package.json)
+diffguard --base main /path/to/ts-repo
+diffguard --paths src/auth/,src/billing/ /path/to/ts-repo
+
 # Skip mutation testing (fastest)
 diffguard --skip-mutation /path/to/repo
 
@@ -70,6 +74,40 @@ diffguard \
 
 **Generated-file skipping (`--skip-generated`):** Enabled by default. Files marked with a standard generated-code banner such as `Code generated ... DO NOT EDIT` are excluded before they reach any analyzer. Pass `--skip-generated=false` to include them.
 
+## Languages
+
+Diffguard auto-detects supported languages from the files it sees. No flag selects the language — analyzers activate on their own file types.
+
+| Language   | Files          | Test runner                                                                    |
+|------------|----------------|--------------------------------------------------------------------------------|
+| Go         | `*.go`         | `go test`                                                                      |
+| TypeScript | `*.ts`, `*.tsx`| Auto-detected from `package.json`: `npx vitest run` → `npx jest` → `npm test`  |
+
+**TypeScript prerequisites.** `node` and `npm` (or `npx`) must be on `PATH` for mutation testing. The TypeScript analyzer only activates when the repo has a `package.json` AND at least one `.ts` / `.tsx` file, so pure-JS projects are left alone. Test files (`*.test.ts`, `*.spec.ts`, `*.test.tsx`, `*.spec.tsx`, or anything under a `__tests__` / `__mocks__` segment) are excluded from mutation. Mutation testing spawns the detected runner once per mutant, so expect TS runs to take longer than Go runs (node startup + TS compile per mutant) — use `--mutation-sample-rate` for fast PR feedback.
+
+### TypeScript example
+
+```bash
+# Go install once
+go install github.com/0xPolygon/diffguard/cmd/diffguard@latest
+
+# From your TypeScript repo, PR-style diff mode with a 20% mutation sample
+cd /path/to/ts-repo
+diffguard --mutation-sample-rate 20 --base origin/main .
+
+# Or scope to specific subdirectories in refactoring mode
+diffguard --paths src/billing/,src/auth/ .
+```
+
+In GitHub Actions, add `actions/setup-node` and an `npm ci` step to the [Per-PR gate workflow](#github-actions) below so `npx vitest` / `npx jest` are available when diffguard spawns mutant runs. The extra steps, inserted after `actions/setup-go`:
+
+```yaml
+- uses: actions/setup-node@v4
+  with:
+    node-version: '20'
+- run: npm ci   # installs vitest / jest so diffguard can invoke them per mutant
+```
+
 ## What It Measures
 
 ### Cognitive Complexity

cmd/diffguard/main.go

@@ -16,6 +16,7 @@ import (
 	"github.com/0xPolygon/diffguard/internal/diff"
 	"github.com/0xPolygon/diffguard/internal/lang"
 	_ "github.com/0xPolygon/diffguard/internal/lang/goanalyzer"
+	_ "github.com/0xPolygon/diffguard/internal/lang/tsanalyzer"
 	"github.com/0xPolygon/diffguard/internal/mutation"
 	"github.com/0xPolygon/diffguard/internal/report"
 	"github.com/0xPolygon/diffguard/internal/sizes"

go.mod

@@ -1,3 +1,5 @@
 module github.com/0xPolygon/diffguard
 
 go 1.26.1
+
+require github.com/smacker/go-tree-sitter v0.0.0-20240827094217-dd81d9e9be82

go.sum

@@ -0,0 +1,10 @@
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/smacker/go-tree-sitter v0.0.0-20240827094217-dd81d9e9be82 h1:6C8qej6f1bStuePVkLSFxoU22XBS165D3klxlzRg8F4=
+github.com/smacker/go-tree-sitter v0.0.0-20240827094217-dd81d9e9be82/go.mod h1:xe4pgH49k4SsmkQq5OT8abwhWmnzkhpgnXeekbx2efw=
+github.com/stretchr/testify v1.9.0 h1:HtqpIVDClZ4nwg75+f6Lvsy/wHu+3BoSGCbBAcpTsTg=
+github.com/stretchr/testify v1.9.0/go.mod h1:r2ic/lqez/lEtzL7wO/rwa5dbSLXVDPFyf8C91i36aY=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=