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/lintcmd/format.go

@@ -0,0 +1,161 @@
+package lintcmd
+
+import (
+	"encoding/json"
+	"fmt"
+	"go/token"
+	"io"
+	"os"
+	"path/filepath"
+	"text/tabwriter"
+
+	"honnef.co/go/tools/analysis/lint"
+)
+
+func shortPath(path string) string {
+	cwd, err := os.Getwd()
+	if err != nil {
+		return path
+	}
+	if rel, err := filepath.Rel(cwd, path); err == nil && len(rel) < len(path) {
+		return rel
+	}
+	return path
+}
+
+func relativePositionString(pos token.Position) string {
+	s := shortPath(pos.Filename)
+	if pos.IsValid() {
+		if s != "" {
+			s += ":"
+		}
+		s += fmt.Sprintf("%d:%d", pos.Line, pos.Column)
+	}
+	if s == "" {
+		s = "-"
+	}
+	return s
+}
+
+type statter interface {
+	Stats(total, errors, warnings, ignored int)
+}
+
+type formatter interface {
+	Format(checks []*lint.Analyzer, diagnostics []diagnostic)
+}
+
+type textFormatter struct {
+	W io.Writer
+}
+
+func (o textFormatter) Format(_ []*lint.Analyzer, ps []diagnostic) {
+	for _, p := range ps {
+		fmt.Fprintf(o.W, "%s: %s\n", relativePositionString(p.Position), p.String())
+		for _, r := range p.Related {
+			fmt.Fprintf(o.W, "\t%s: %s\n", relativePositionString(r.Position), r.Message)
+		}
+	}
+}
+
+type nullFormatter struct{}
+
+func (nullFormatter) Format([]*lint.Analyzer, []diagnostic) {}
+
+type jsonFormatter struct {
+	W io.Writer
+}
+
+func (o jsonFormatter) Format(_ []*lint.Analyzer, ps []diagnostic) {
+	type location struct {
+		File   string `json:"file"`
+		Line   int    `json:"line"`
+		Column int    `json:"column"`
+	}
+	type related struct {
+		Location location `json:"location"`
+		End      location `json:"end"`
+		Message  string   `json:"message"`
+	}
+
+	enc := json.NewEncoder(o.W)
+	for _, p := range ps {
+		jp := struct {
+			Code     string    `json:"code"`
+			Severity string    `json:"severity,omitempty"`
+			Location location  `json:"location"`
+			End      location  `json:"end"`
+			Message  string    `json:"message"`
+			Related  []related `json:"related,omitempty"`
+		}{
+			Code:     p.Category,
+			Severity: p.Severity.String(),
+			Location: location{
+				File:   p.Position.Filename,
+				Line:   p.Position.Line,
+				Column: p.Position.Column,
+			},
+			End: location{
+				File:   p.End.Filename,
+				Line:   p.End.Line,
+				Column: p.End.Column,
+			},
+			Message: p.Message,
+		}
+		for _, r := range p.Related {
+			jp.Related = append(jp.Related, related{
+				Location: location{
+					File:   r.Position.Filename,
+					Line:   r.Position.Line,
+					Column: r.Position.Column,
+				},
+				End: location{
+					File:   r.End.Filename,
+					Line:   r.End.Line,
+					Column: r.End.Column,
+				},
+				Message: r.Message,
+			})
+		}
+		_ = enc.Encode(jp)
+	}
+}
+
+type stylishFormatter struct {
+	W io.Writer
+
+	prevFile string
+	tw       *tabwriter.Writer
+}
+
+func (o *stylishFormatter) Format(_ []*lint.Analyzer, ps []diagnostic) {
+	for _, p := range ps {
+		pos := p.Position
+		if pos.Filename == "" {
+			pos.Filename = "-"
+		}
+
+		if pos.Filename != o.prevFile {
+			if o.prevFile != "" {
+				o.tw.Flush()
+				fmt.Fprintln(o.W)
+			}
+			fmt.Fprintln(o.W, pos.Filename)
+			o.prevFile = pos.Filename
+			o.tw = tabwriter.NewWriter(o.W, 0, 4, 2, ' ', 0)
+		}
+		fmt.Fprintf(o.tw, "  (%d, %d)\t%s\t%s\n", pos.Line, pos.Column, p.Category, p.Message)
+		for _, r := range p.Related {
+			fmt.Fprintf(o.tw, "    (%d, %d)\t\t  %s\n", r.Position.Line, r.Position.Column, r.Message)
+		}
+	}
+}
+
+func (o *stylishFormatter) Stats(total, errors, warnings, ignored int) {
+	if o.tw != nil {
+		o.tw.Flush()
+		fmt.Fprintln(o.W)
+	}
+	fmt.Fprintf(o.W, " ✖ %d problems (%d errors, %d warnings, %d ignored)\n",
+		total, errors, warnings, ignored)
+}