Add some color to the relevant filenames in terminal log

Fixes gohugoio#5344

common/herrors/error_locator.go

@@ -18,15 +18,23 @@ import (
 	"fmt"
 	"io"
 	"io/ioutil"
+	"os"
 	"strings"
 
+	"github.com/gohugoio/hugo/common/terminal"
 	"github.com/gohugoio/hugo/helpers"
 
 	"github.com/spf13/afero"
 )
 
 var fileErrorFormat = "\"%s:%d:%d\": %s"
 
+func init() {
+	if terminal.IsTerminal(os.Stdout) {
+		fileErrorFormat = terminal.Notice("\"%s:%d:%d\"") + ": %s"
+	}
+}
+
 // LineMatcher contains the elements used to match an error to a line
 type LineMatcher struct {
 	FileError  FileError

common/terminal/colors.go

@@ -0,0 +1,53 @@
+// Copyright 2018 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package terminal contains helper for the terminal, such as coloring output.
+package terminal
+
+import (
+	"fmt"
+	"os"
+	"strings"
+
+	isatty "github.com/mattn/go-isatty"
+)
+
+const (
+	noticeColor = "\033[1;36m%s\033[0m"
+)
+
+// IsTerminal return true if the file descriptor is terminal and the TERM
+// environment variable isn't a dumb one.
+func IsTerminal(f *os.File) bool {
+	fd := f.Fd()
+	return os.Getenv("TERM") != "dumb" && (isatty.IsTerminal(fd) || isatty.IsCygwinTerminal(fd))
+}
+
+// Notice colorizes the string in a noticeable color.
+func Notice(s string) string {
+	return colorize(s, noticeColor)
+}
+
+// colorize s in color.
+func colorize(s, color string) string {
+	s = fmt.Sprintf(color, doublePercent(s))
+	return singlePercent(s)
+}
+
+func doublePercent(str string) string {
+	return strings.Replace(str, "%", "%%", -1)
+}
+
+func singlePercent(str string) string {
+	return strings.Replace(str, "%%", "%", -1)
+}

go.mod

@@ -29,7 +29,7 @@ require (
 	github.com/kyokomi/emoji v1.5.1
 	github.com/magefile/mage v1.4.0
 	github.com/markbates/inflect v1.0.0
-	github.com/mattn/go-isatty v0.0.4 // indirect
+	github.com/mattn/go-isatty v0.0.4
 	github.com/mattn/go-runewidth v0.0.3 // indirect
 	github.com/miekg/mmark v1.3.6
 	github.com/mitchellh/hashstructure v1.0.0