1 files changed, 255 insertions, 0 deletions
diff --git a/common/herrors/error_locator.go b/common/herrors/error_locator.go
new file mode 100644
index 000000000..3778a3729
--- /dev/null
+++ b/common/herrors/error_locator.go
@@ -0,0 +1,255 @@
+// 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 errors contains common Hugo errors and error related utilities.
+package herrors
+
+import (
+	"io"
+	"io/ioutil"
+	"path/filepath"
+	"strings"
+
+	"github.com/gohugoio/hugo/common/text"
+
+	"github.com/spf13/afero"
+)
+
+// LineMatcher contains the elements used to match an error to a line
+type LineMatcher struct {
+	Position text.Position
+	Error    error
+
+	LineNumber int
+	Offset     int
+	Line       string
+}
+
+// LineMatcherFn is used to match a line with an error.
+type LineMatcherFn func(m LineMatcher) bool
+
+// SimpleLineMatcher simply matches by line number.
+var SimpleLineMatcher = func(m LineMatcher) bool {
+	return m.Position.LineNumber == m.LineNumber
+}
+
+var _ text.Positioner = ErrorContext{}
+
+// ErrorContext contains contextual information about an error. This will
+// typically be the lines surrounding some problem in a file.
+type ErrorContext struct {
+
+	// If a match will contain the matched line and up to 2 lines before and after.
+	// Will be empty if no match.
+	Lines []string
+
+	// The position of the error in the Lines above. 0 based.
+	LinesPos int
+
+	position text.Position
+
+	// The lexer to use for syntax highlighting.
+	// https://gohugo.io/content-management/syntax-highlighting/#list-of-chroma-highlighting-languages
+	ChromaLexer string
+}
+
+// Position returns the text position of this error.
+func (e ErrorContext) Position() text.Position {
+	return e.position
+}
+
+var _ causer = (*ErrorWithFileContext)(nil)
+
+// ErrorWithFileContext is an error with some additional file context related
+// to that error.
+type ErrorWithFileContext struct {
+	cause error
+	ErrorContext
+}
+
+func (e *ErrorWithFileContext) Error() string {
+	pos := e.Position()
+	if pos.IsValid() {
+		return pos.String() + ": " + e.cause.Error()
+	}
+	return e.cause.Error()
+}
+
+func (e *ErrorWithFileContext) Cause() error {
+	return e.cause
+}
+
+// WithFileContextForFile will try to add a file context with lines matching the given matcher.
+// If no match could be found, the original error is returned with false as the second return value.
+func WithFileContextForFile(e error, realFilename, filename string, fs afero.Fs, matcher LineMatcherFn) (error, bool) {
+	f, err := fs.Open(filename)
+	if err != nil {
+		return e, false
+	}
+	defer f.Close()
+	return WithFileContext(e, realFilename, f, matcher)
+}
+
+// WithFileContextForFile will try to add a file context with lines matching the given matcher.
+// If no match could be found, the original error is returned with false as the second return value.
+func WithFileContext(e error, realFilename string, r io.Reader, matcher LineMatcherFn) (error, bool) {
+	if e == nil {
+		panic("error missing")
+	}
+	le := UnwrapFileError(e)
+
+	if le == nil {
+		var ok bool
+		if le, ok = ToFileError("", e).(FileError); !ok {
+			return e, false
+		}
+	}
+
+	var errCtx ErrorContext
+
+	posle := le.Position()
+
+	if posle.Offset != -1 {
+		errCtx = locateError(r, le, func(m LineMatcher) bool {
+			if posle.Offset >= m.Offset && posle.Offset < m.Offset+len(m.Line) {
+				lno := posle.LineNumber - m.Position.LineNumber + m.LineNumber
+				m.Position = text.Position{LineNumber: lno}
+			}
+			return matcher(m)
+		})
+	} else {
+		errCtx = locateError(r, le, matcher)
+	}
+
+	pos := &errCtx.position
+
+	if pos.LineNumber == -1 {
+		return e, false
+	}
+
+	pos.Filename = realFilename
+
+	if le.Type() != "" {
+		errCtx.ChromaLexer = chromaLexerFromType(le.Type())
+	} else {
+		errCtx.ChromaLexer = chromaLexerFromFilename(realFilename)
+	}
+
+	return &ErrorWithFileContext{cause: e, ErrorContext: errCtx}, true
+}
+
+// UnwrapErrorWithFileContext tries to unwrap an ErrorWithFileContext from err.
+// It returns nil if this is not possible.
+func UnwrapErrorWithFileContext(err error) *ErrorWithFileContext {
+	for err != nil {
+		switch v := err.(type) {
+		case *ErrorWithFileContext:
+			return v
+		case causer:
+			err = v.Cause()
+		default:
+			return nil
+		}
+	}
+	return nil
+}
+
+func chromaLexerFromType(fileType string) string {
+	switch fileType {
+	case "html", "htm":
+		return "go-html-template"
+	}
+	return fileType
+}
+
+func extNoDelimiter(filename string) string {
+	return strings.TrimPrefix(filepath.Ext(filename), ".")
+}
+
+func chromaLexerFromFilename(filename string) string {
+	if strings.Contains(filename, "layouts") {
+		return "go-html-template"
+	}
+
+	ext := extNoDelimiter(filename)
+	return chromaLexerFromType(ext)
+}
+
+func locateErrorInString(src string, matcher LineMatcherFn) ErrorContext {
+	return locateError(strings.NewReader(src), &fileError{}, matcher)
+}
+
+func locateError(r io.Reader, le FileError, matches LineMatcherFn) ErrorContext {
+	if le == nil {
+		panic("must provide an error")
+	}
+
+	errCtx := ErrorContext{position: text.Position{LineNumber: -1, ColumnNumber: 1, Offset: -1}, LinesPos: -1}
+
+	b, err := ioutil.ReadAll(r)
+	if err != nil {
+		return errCtx
+	}
+
+	pos := &errCtx.position
+	lepos := le.Position()
+
+	lines := strings.Split(string(b), "\n")
+
+	if lepos.ColumnNumber >= 0 {
+		pos.ColumnNumber = lepos.ColumnNumber
+	}
+
+	lineNo := 0
+	posBytes := 0
+
+	for li, line := range lines {
+		lineNo = li + 1
+		m := LineMatcher{
+			Position:   le.Position(),
+			Error:      le,
+			LineNumber: lineNo,
+			Offset:     posBytes,
+			Line:       line,
+		}
+		if errCtx.LinesPos == -1 && matches(m) {
+			pos.LineNumber = lineNo
+			break
+		}
+
+		posBytes += len(line)
+	}
+
+	if pos.LineNumber != -1 {
+		low := pos.LineNumber - 3
+		if low < 0 {
+			low = 0
+		}
+
+		if pos.LineNumber > 2 {
+			errCtx.LinesPos = 2
+		} else {
+			errCtx.LinesPos = pos.LineNumber - 1
+		}
+
+		high := pos.LineNumber + 2
+		if high > len(lines) {
+			high = len(lines)
+		}
+
+		errCtx.Lines = lines[low:high]
+
+	}
+
+	return errCtx
+}