🚨 Add some tooling/ linting

.gitignore

@@ -0,0 +1,25 @@
+# If you prefer the allow list template instead of the deny list, see community template:
+# https://github.com/github/gitignore/blob/main/community/Golang/Go.AllowList.gitignore
+#
+# Binaries for programs and plugins
+*.exe
+*.exe~
+*.dll
+*.so
+*.dylib
+
+# Test binary, built with `go test -c`
+*.test
+
+# Dependency directories
+vendor/
+
+# Go workspace file
+go.work
+go.work.sum
+
+# env file
+.env
+
+build/
+.task/

.golangci.yaml

@@ -0,0 +1,48 @@
+version: "2"
+
+linters:
+  enable:
+    - errcheck
+    - govet
+    - ineffassign
+    - staticcheck
+    - unused
+    - copyloopvar
+    - dupl
+    - err113
+    - errname
+    - exptostd
+    - fatcontext
+    - funlen
+    - gocognit
+    - goconst
+    - gocritic
+    - gocyclo
+    - godot
+    - godox
+    - gosec
+    - perfsprint
+    - testifylint
+  exclusions:
+    rules:
+      - path: '(.+)_test\.go'
+        linters:
+          - errcheck
+          - err113
+          - gosec
+          - gocognit
+          - gocyclo
+  settings:
+    testifylint:
+      enable-all: true
+      disable:
+        - require-error
+    gocognit:
+      min-complexity: 10
+    gocyclo:
+      min-complexity: 10
+    gocritic:
+      enable-all: true
+      settings:
+        hugeParam:
+          sizeThreshold: 255

Taskfile.yml

@@ -0,0 +1,39 @@
+# https://taskfile.dev
+
+version: '3'
+
+vars:
+  GOBIN_ENV:
+    sh: go env GOBIN
+  GOPATH_ENV:
+    sh: go env GOPATH
+  BIN: '{{if .GOBIN_ENV}}{{.GOBIN_ENV}}{{else}}{{.GOPATH_ENV}}/bin{{end}}'
+
+tasks:
+  default:
+    desc: fmt, lint, test
+    deps:
+      - fmt
+      - lint
+      - test
+
+  fmt:
+    desc: Format go files
+    sources:
+      - "*.go"
+    cmds:
+      - go fmt ./...
+
+  lint:
+    desc: Statically analyze code
+    sources:
+      - '*.go'
+    cmds:
+      - golangci-lint run
+
+  test:
+    desc: Run all tests
+    sources:
+      - '*.go'
+    cmds:
+      - go test -cover -race .

errgroup.go

@@ -131,6 +131,12 @@ func (g *Group) TryGo(f func() error) bool {
 	return true
 }
 
+type ErrgroupLimitError struct{ Size int }
+
+func (egerr *ErrgroupLimitError) Error() string {
+	return fmt.Sprintf("errgroup: modify limit while %v goroutines in the group are still active", egerr.Size)
+}
+
 // SetLimit limits the number of active goroutines in this group to at most n.
 // A negative value indicates no limit.
 // A limit of zero will prevent any new goroutines from being added.
@@ -145,7 +151,8 @@ func (g *Group) SetLimit(n int) {
 		return
 	}
 	if len(g.sem) != 0 {
-		panic(fmt.Errorf("errgroup: modify limit while %v goroutines in the group are still active", len(g.sem)))
+		var err error = &ErrgroupLimitError{len(g.sem)}
+		panic(err)
 	}
 	g.sem = make(chan token, n)
 }

errgroup_test.go

@@ -43,8 +43,6 @@ func ExampleGroup_justErrors() {
 		"http://www.somestupidname.com/",
 	}
 	for _, url := range urls {
-		// Launch a goroutine to fetch the URL.
-		url := url // https://golang.org/doc/faq#closures_and_goroutines
 		g.Go(func() error {
 			// Fetch the URL.
 			resp, err := http.Get(url)
@@ -71,7 +69,6 @@ func ExampleGroup_parallel() {
 		searches := []Search{Web, Image, Video}
 		results := make([]Result, len(searches))
 		for i, search := range searches {
-			i, search := i, search // https://golang.org/doc/faq#closures_and_goroutines
 			g.Go(func() error {
 				result, err := search(ctx, query)
 				if err == nil {
@@ -120,7 +117,6 @@ func TestZeroGroup(t *testing.T) {
 
 		var firstErr error
 		for i, err := range tc.errs {
-			err := err
 			g.Go(func() error { return err })
 
 			if firstErr == nil && err != nil {
@@ -153,7 +149,6 @@ func TestWithContext(t *testing.T) {
 		g, ctx := errgroup.WithContext(context.Background())
 
 		for _, err := range tc.errs {
-			err := err
 			g.Go(func() error { return err })
 		}
 
@@ -267,7 +262,6 @@ func TestCancelCause(t *testing.T) {
 		g, ctx := errgroup.WithContext(context.Background())
 
 		for _, err := range tc.errs {
-			err := err
 			g.TryGo(func() error { return err })
 		}