commands: Show server error info in browser

The main item in this commit is showing of errors with a file context when running `hugo server`.

This can be turned off: `hugo server --disableBrowserError` (can also be set in `config.toml`).

But to get there, the error handling in Hugo needed a revision. There are some items left TODO for commits soon to follow, most notable errors in content and config files.

Fixes #5284
Fixes #5290
See #5325
See #5324

hugolib/hugo_sites_build_errors_test.go

@@ -0,0 +1,182 @@
+package hugolib
+
+import (
+	"fmt"
+	"strings"
+	"testing"
+
+	"github.com/gohugoio/hugo/common/herrors"
+	"github.com/stretchr/testify/require"
+)
+
+type testSiteBuildErrorAsserter struct {
+	name   string
+	assert *require.Assertions
+}
+
+func (t testSiteBuildErrorAsserter) getFileError(err error) *herrors.ErrorWithFileContext {
+	t.assert.NotNil(err, t.name)
+	ferr := herrors.UnwrapErrorWithFileContext(err)
+	t.assert.NotNil(ferr, fmt.Sprintf("[%s] got %T: %+v", t.name, err, err))
+	return ferr
+}
+
+func (t testSiteBuildErrorAsserter) assertLineNumber(lineNumber int, err error) {
+	fe := t.getFileError(err)
+	t.assert.Equal(lineNumber, fe.LineNumber, fmt.Sprintf("[%s]  got => %s", t.name, fe))
+}
+
+func TestSiteBuildErrors(t *testing.T) {
+	t.Parallel()
+	assert := require.New(t)
+
+	const (
+		yamlcontent = "yamlcontent"
+		shortcode   = "shortcode"
+		base        = "base"
+		single      = "single"
+	)
+
+	// TODO(bep) add content tests after https://github.com/gohugoio/hugo/issues/5324
+	// is implemented.
+
+	tests := []struct {
+		name              string
+		fileType          string
+		fileFixer         func(content string) string
+		assertCreateError func(a testSiteBuildErrorAsserter, err error)
+		assertBuildError  func(a testSiteBuildErrorAsserter, err error)
+	}{
+
+		{
+			name:     "Base template parse failed",
+			fileType: base,
+			fileFixer: func(content string) string {
+				return strings.Replace(content, ".Title }}", ".Title }", 1)
+			},
+			assertCreateError: func(a testSiteBuildErrorAsserter, err error) {
+				a.assertLineNumber(2, err)
+			},
+		},
+		{
+			name:     "Base template execute failed",
+			fileType: base,
+			fileFixer: func(content string) string {
+				return strings.Replace(content, ".Title", ".Titles", 1)
+			},
+			assertBuildError: func(a testSiteBuildErrorAsserter, err error) {
+				a.assertLineNumber(2, err)
+			},
+		},
+		{
+			name:     "Single template parse failed",
+			fileType: single,
+			fileFixer: func(content string) string {
+				return strings.Replace(content, ".Title }}", ".Title }", 1)
+			},
+			assertCreateError: func(a testSiteBuildErrorAsserter, err error) {
+				a.assertLineNumber(3, err)
+			},
+		},
+		{
+			name:     "Single template execute failed",
+			fileType: single,
+			fileFixer: func(content string) string {
+				return strings.Replace(content, ".Title", ".Titles", 1)
+			},
+			assertBuildError: func(a testSiteBuildErrorAsserter, err error) {
+				a.assertLineNumber(3, err)
+			},
+		},
+		{
+			name:     "Shortcode parse failed",
+			fileType: shortcode,
+			fileFixer: func(content string) string {
+				return strings.Replace(content, ".Title }}", ".Title }", 1)
+			},
+			assertCreateError: func(a testSiteBuildErrorAsserter, err error) {
+				a.assertLineNumber(2, err)
+			},
+		},
+		// TODO(bep) 2errors
+		/*		{
+				name:     "Shortode execute failed",
+				fileType: shortcode,
+				fileFixer: func(content string) string {
+					return strings.Replace(content, ".Title", ".Titles", 1)
+				},
+				assertBuildError: func(a testSiteBuildErrorAsserter, err error) {
+					a.assertLineNumber(2, err)
+				},
+			},*/
+	}
+
+	for _, test := range tests {
+
+		errorAsserter := testSiteBuildErrorAsserter{
+			assert: assert,
+			name:   test.name,
+		}
+
+		b := newTestSitesBuilder(t).WithSimpleConfigFile()
+
+		f := func(fileType, content string) string {
+			if fileType != test.fileType {
+				return content
+			}
+			return test.fileFixer(content)
+
+		}
+
+		b.WithTemplatesAdded("layouts/shortcodes/sc.html", f(shortcode, `SHORTCODE L1
+SHORTCODE L2
+SHORTCODE L3:
+SHORTCODE L4: {{ .Page.Title }}
+`))
+		b.WithTemplatesAdded("layouts/_default/baseof.html", f(base, `BASEOF L1
+BASEOF L2
+BASEOF L3
+BASEOF L4{{ if .Title }}{{ end }}
+{{block "main" .}}This is the main content.{{end}}
+BASEOF L6
+`))
+
+		b.WithTemplatesAdded("layouts/_default/single.html", f(single, `{{ define "main" }}
+SINGLE L2:
+SINGLE L3:
+SINGLE L4:
+SINGLE L5: {{ .Title }} {{ .Content }}
+{{ end }}
+`))
+
+		b.WithContent("myyaml.md", f(yamlcontent, `---
+title: "The YAML"
+---
+
+Some content.
+
+{{< sc >}}
+
+Some more text.
+
+The end.
+
+`))
+
+		createErr := b.CreateSitesE()
+		if test.assertCreateError != nil {
+			test.assertCreateError(errorAsserter, createErr)
+		} else {
+			assert.NoError(createErr)
+		}
+
+		if createErr == nil {
+			buildErr := b.BuildE(BuildCfg{})
+			if test.assertBuildError != nil {
+				test.assertBuildError(errorAsserter, buildErr)
+			} else {
+				assert.NoError(buildErr)
+			}
+		}
+	}
+}