staticcheck (#313)

* CI: use staticcheck for linting

This commit switches the linter for Go code from golint to staticcheck.
Golint has been deprecated since last year and staticcheck is a
recommended replacement.

Signed-off-by: Lucas Servén Marín <lserven@gmail.com>

* revendor

Signed-off-by: Lucas Servén Marín <lserven@gmail.com>

* cmd,pkg: fix lint warnings

Signed-off-by: Lucas Servén Marín <lserven@gmail.com>

vendor/honnef.co/go/tools/analysis/report/report.go

@@ -0,0 +1,247 @@
+package report
+
+import (
+	"bytes"
+	"fmt"
+	"go/ast"
+	"go/format"
+	"go/token"
+	"path/filepath"
+	"strconv"
+	"strings"
+
+	"honnef.co/go/tools/analysis/facts"
+	"honnef.co/go/tools/go/ast/astutil"
+
+	"golang.org/x/tools/go/analysis"
+)
+
+type Options struct {
+	ShortRange      bool
+	FilterGenerated bool
+	Fixes           []analysis.SuggestedFix
+	Related         []analysis.RelatedInformation
+}
+
+type Option func(*Options)
+
+func ShortRange() Option {
+	return func(opts *Options) {
+		opts.ShortRange = true
+	}
+}
+
+func FilterGenerated() Option {
+	return func(opts *Options) {
+		opts.FilterGenerated = true
+	}
+}
+
+func Fixes(fixes ...analysis.SuggestedFix) Option {
+	return func(opts *Options) {
+		opts.Fixes = append(opts.Fixes, fixes...)
+	}
+}
+
+func Related(node Positioner, message string) Option {
+	return func(opts *Options) {
+		pos, end, ok := getRange(node, opts.ShortRange)
+		if !ok {
+			return
+		}
+		r := analysis.RelatedInformation{
+			Pos:     pos,
+			End:     end,
+			Message: message,
+		}
+		opts.Related = append(opts.Related, r)
+	}
+}
+
+type Positioner interface {
+	Pos() token.Pos
+}
+
+type fullPositioner interface {
+	Pos() token.Pos
+	End() token.Pos
+}
+
+type sourcer interface {
+	Source() ast.Node
+}
+
+// shortRange returns the position and end of the main component of an
+// AST node. For nodes that have no body, the short range is identical
+// to the node's Pos and End. For nodes that do have a body, the short
+// range excludes the body.
+func shortRange(node ast.Node) (pos, end token.Pos) {
+	switch node := node.(type) {
+	case *ast.File:
+		return node.Pos(), node.Name.End()
+	case *ast.CaseClause:
+		return node.Pos(), node.Colon + 1
+	case *ast.CommClause:
+		return node.Pos(), node.Colon + 1
+	case *ast.DeferStmt:
+		return node.Pos(), node.Defer + token.Pos(len("defer"))
+	case *ast.ExprStmt:
+		return shortRange(node.X)
+	case *ast.ForStmt:
+		if node.Post != nil {
+			return node.For, node.Post.End()
+		} else if node.Cond != nil {
+			return node.For, node.Cond.End()
+		} else if node.Init != nil {
+			// +1 to catch the semicolon, for gofmt'ed code
+			return node.Pos(), node.Init.End() + 1
+		} else {
+			return node.Pos(), node.For + token.Pos(len("for"))
+		}
+	case *ast.FuncDecl:
+		return node.Pos(), node.Type.End()
+	case *ast.FuncLit:
+		return node.Pos(), node.Type.End()
+	case *ast.GoStmt:
+		if _, ok := astutil.Unparen(node.Call.Fun).(*ast.FuncLit); ok {
+			return node.Pos(), node.Go + token.Pos(len("go"))
+		} else {
+			return node.Pos(), node.End()
+		}
+	case *ast.IfStmt:
+		return node.Pos(), node.Cond.End()
+	case *ast.RangeStmt:
+		return node.Pos(), node.X.End()
+	case *ast.SelectStmt:
+		return node.Pos(), node.Pos() + token.Pos(len("select"))
+	case *ast.SwitchStmt:
+		if node.Tag != nil {
+			return node.Pos(), node.Tag.End()
+		} else if node.Init != nil {
+			// +1 to catch the semicolon, for gofmt'ed code
+			return node.Pos(), node.Init.End() + 1
+		} else {
+			return node.Pos(), node.Pos() + token.Pos(len("switch"))
+		}
+	case *ast.TypeSwitchStmt:
+		return node.Pos(), node.Assign.End()
+	default:
+		return node.Pos(), node.End()
+	}
+}
+
+func HasRange(node Positioner) bool {
+	// we don't know if getRange will be called with shortRange set to
+	// true, so make sure that both work.
+	_, _, ok := getRange(node, false)
+	if !ok {
+		return false
+	}
+	_, _, ok = getRange(node, true)
+	return ok
+}
+
+func getRange(node Positioner, short bool) (pos, end token.Pos, ok bool) {
+	switch n := node.(type) {
+	case sourcer:
+		s := n.Source()
+		if s == nil {
+			return 0, 0, false
+		}
+		if short {
+			p, e := shortRange(s)
+			return p, e, true
+		}
+		return s.Pos(), s.End(), true
+	case fullPositioner:
+		if short {
+			p, e := shortRange(n)
+			return p, e, true
+		}
+		return n.Pos(), n.End(), true
+	default:
+		return n.Pos(), token.NoPos, true
+	}
+}
+
+func Report(pass *analysis.Pass, node Positioner, message string, opts ...Option) {
+	cfg := &Options{}
+	for _, opt := range opts {
+		opt(cfg)
+	}
+
+	file := DisplayPosition(pass.Fset, node.Pos()).Filename
+	if cfg.FilterGenerated {
+		m := pass.ResultOf[facts.Generated].(map[string]facts.Generator)
+		if _, ok := m[file]; ok {
+			return
+		}
+	}
+
+	pos, end, ok := getRange(node, cfg.ShortRange)
+	if !ok {
+		panic(fmt.Sprintf("no valid position for reporting node %v", node))
+	}
+	d := analysis.Diagnostic{
+		Pos:            pos,
+		End:            end,
+		Message:        message,
+		SuggestedFixes: cfg.Fixes,
+		Related:        cfg.Related,
+	}
+	pass.Report(d)
+}
+
+func Render(pass *analysis.Pass, x interface{}) string {
+	var buf bytes.Buffer
+	if err := format.Node(&buf, pass.Fset, x); err != nil {
+		panic(err)
+	}
+	return buf.String()
+}
+
+func RenderArgs(pass *analysis.Pass, args []ast.Expr) string {
+	var ss []string
+	for _, arg := range args {
+		ss = append(ss, Render(pass, arg))
+	}
+	return strings.Join(ss, ", ")
+}
+
+func DisplayPosition(fset *token.FileSet, p token.Pos) token.Position {
+	if p == token.NoPos {
+		return token.Position{}
+	}
+
+	// Only use the adjusted position if it points to another Go file.
+	// This means we'll point to the original file for cgo files, but
+	// we won't point to a YACC grammar file.
+	pos := fset.PositionFor(p, false)
+	adjPos := fset.PositionFor(p, true)
+
+	if filepath.Ext(adjPos.Filename) == ".go" {
+		return adjPos
+	}
+
+	return pos
+}
+
+func Ordinal(n int) string {
+	suffix := "th"
+	if n < 10 || n > 20 {
+		switch n % 10 {
+		case 0:
+			suffix = "th"
+		case 1:
+			suffix = "st"
+		case 2:
+			suffix = "nd"
+		case 3:
+			suffix = "rd"
+		default:
+			suffix = "th"
+		}
+	}
+
+	return strconv.Itoa(n) + suffix
+}