Add cross-compilation Makefile targets and tar-based releases.

Revamp the build system to be more inline with other Prometheus exporters.
Notably add Darwin and Windows build targets, and add support for releases
using tar files.

tools/vendor/github.com/alecthomas/gometalinter/config.go

@@ -8,12 +8,12 @@ import (
 )
 
 // Config for gometalinter. This can be loaded from a JSON file with --config.
-type Config struct { // nolint: aligncheck
-	// A map of linter name to "<command>:<pattern>".
+type Config struct { // nolint: maligned
+	// A map from linter name -> <LinterConfig|string>.
 	//
-	// <command> should always include {path} as the target directory to execute. Globs in <command>
-	// are expanded by gometalinter (not by the shell).
-	Linters map[string]string
+	// For backwards compatibility, the value stored in the JSON blob can also
+	// be a string of the form "<command>:<pattern>".
+	Linters map[string]StringOrLinterConfig
 
 	// The set of linters that should be enabled.
 	Enable  []string
@@ -51,6 +51,35 @@ type Config struct { // nolint: aligncheck
 	EnableGC        bool
 	Aggregate       bool
 	EnableAll       bool
+
+	// Warn if a nolint directive was never matched to a linter issue
+	WarnUnmatchedDirective bool
+
+	formatTemplate *template.Template
+}
+
+type StringOrLinterConfig LinterConfig
+
+func (c *StringOrLinterConfig) UnmarshalJSON(raw []byte) error {
+	var linterConfig LinterConfig
+	// first try to un-marshall directly into struct
+	origErr := json.Unmarshal(raw, &linterConfig)
+	if origErr == nil {
+		*c = StringOrLinterConfig(linterConfig)
+		return nil
+	}
+
+	// i.e. bytes didn't represent the struct, treat them as a string
+	var linterSpec string
+	if err := json.Unmarshal(raw, &linterSpec); err != nil {
+		return origErr
+	}
+	linter, err := parseLinterConfigSpec("", linterSpec)
+	if err != nil {
+		return err
+	}
+	*c = StringOrLinterConfig(linter)
+	return nil
 }
 
 type jsonDuration time.Duration
@@ -70,17 +99,16 @@ func (td *jsonDuration) Duration() time.Duration {
 	return time.Duration(*td)
 }
 
-// TODO: should be a field on Config struct
-var formatTemplate = &template.Template{}
-
 var sortKeys = []string{"none", "path", "line", "column", "severity", "message", "linter"}
 
 // Configuration defaults.
 var config = &Config{
-	Format: "{{.Path}}:{{.Line}}:{{if .Col}}{{.Col}}{{end}}:{{.Severity}}: {{.Message}} ({{.Linter}})",
+	Format: DefaultIssueFormat,
 
+	Linters: map[string]StringOrLinterConfig{},
 	Severity: map[string]string{
 		"gotype":  "error",
+		"gotypex": "error",
 		"test":    "error",
 		"testify": "error",
 		"vet":     "error",