Allow dates to be parsed from filenames

docs/content/content/front-matter.md

@@ -1,7 +1,7 @@
 ---
 aliases:
 - /doc/front-matter/
-lastmod: 2015-12-23
+lastmod: 2017-06-29
 date: 2013-07-01
 menu:
   main:
@@ -117,3 +117,12 @@ It's possible to set some options for Markdown rendering in the page's front mat
 
 See [Configuration]({{< ref "overview/configuration.md#configure-blackfriday-rendering" >}}) for more.
 
+## Fallback date variable from filenames
+If you're migrating content to Hugo, you may have content with dates in the filename. For example `2017-01-31-myblog.md`.  You can optionally enable the `filenameDateFallbackPattern` and `filenameDateFallbackFormat` configuration options. These will allow you to fallback on datestamps provided in the filename in place of a date value in the front matter.
+
+As an example, for posts following a YYY-MM-DD-posttitle.md naming convention, you can use:
+
+```
+filenameDateFallbackPattern: "(?P<year>\\d{4})\\-(?P<month>\\d{2})\\-(?P<day>\\d{2})"
+filenameDateFallbackFormat: "2006-01-02"
+```

docs/content/overview/configuration.md

@@ -1,7 +1,7 @@
 ---
 aliases:
 - /doc/configuration/
-lastmod: 2016-09-17
+lastmod: 2017-04-09
 date: 2013-07-01
 linktitle: Configuration
 menu:
@@ -139,6 +139,10 @@ along with their current, default values:
     enableEmoji:				false
     # Show a placeholder instead of the default value or an empty string if a translation is missing
     enableMissingTranslationPlaceholders: false
+    # Regex to use for dates in filenames.
+    filenameDateFallbackPattern: "(?P<year>\\d{4})\\-(?P<month>\\d{2})\\-(?P<day>\\d{2})"
+    # Time format for custom dates in filenames. Must match `filenameDateFallbackPattern`
+    filenameDateFallbackFormat: "2006-01-02"
     footnoteAnchorPrefix:       ""
     footnoteReturnLinkContents: ""
     # google analytics tracking id

hugolib/config.go

@@ -108,6 +108,8 @@ func loadDefaultSettingsFor(v *viper.Viper) {
 	v.SetDefault("enableEmoji", false)
 	v.SetDefault("pygmentsCodeFencesGuessSyntax", false)
 	v.SetDefault("useModTimeAsFallback", false)
+	v.SetDefault("filenameDateFallbackPattern", nil)
+	v.SetDefault("filenameDateFallbackFormat", "2006-01-02")
 	v.SetDefault("defaultContentLanguage", "en")
 	v.SetDefault("defaultContentLanguageInSubdir", false)
 	v.SetDefault("enableMissingTranslationPlaceholders", false)

hugolib/page.go

@@ -1021,6 +1021,14 @@ func (p *Page) update(f interface{}) error {
 			p.Date = fi.ModTime()
 			p.Params["date"] = p.Date
 		}
+	} else if p.Date.IsZero() && p.s.Cfg.GetString("filenameDateFallbackPattern") != "" {
+		dateExp := regexp.MustCompile(p.s.Cfg.GetString("filenameDateFallbackPattern"))
+		dateString := dateExp.FindString(p.File.Path())
+		filenameDate, err := time.Parse(p.s.Cfg.GetString("filenameDateFallbackFormat"), dateString)
+		if err == nil {
+			p.Date = filenameDate
+			p.Params["date"] = p.Date
+		}
 	}
 
 	if p.Lastmod.IsZero() {

hugolib/page_test.go

@@ -95,6 +95,7 @@ Content of the file goes Here
 Content of the file goes Here
 `
 	simplePageRFC3339Date  = "---\ntitle: RFC3339 Date\ndate: \"2013-05-17T16:59:30Z\"\n---\nrfc3339 content"
+	simplePageNoDate       = "---\ntitle: Path Date\n---\n Date param from url"
 	simplePageJSONMultiple = `
 {
 	"title": "foobar",
@@ -847,6 +848,22 @@ func TestPageWithDate(t *testing.T) {
 	checkPageDate(t, p, d)
 }
 
+func TestPageWithDateInFilename(t *testing.T) {
+	t.Parallel()
+	cfg, fs := newTestCfg()
+
+	writeSource(t, fs, filepath.Join("content", "2017-01-31-simple.md"), simplePageNoDate)
+
+	s := buildSingleSite(t, deps.DepsCfg{Fs: fs, Cfg: cfg}, BuildCfg{SkipRender: true})
+
+	require.Len(t, s.RegularPages, 1)
+
+	p := s.RegularPages[0]
+	d, _ := time.Parse(time.RFC3339, "2017-01-31")
+
+	checkPageDate(t, p, d)
+}
+
 func TestWordCountWithAllCJKRunesWithoutHasCJKLanguage(t *testing.T) {
 	t.Parallel()
 	assertFunc := func(t *testing.T, ext string, pages Pages) {