Merge commit 'b9bd35d72e14932fb6588ff62b90cddef0a060fc' as 'docs'

docs/content/en/functions/errorf.md

@@ -0,0 +1,29 @@
+---
+title: errorf
+linktitle: errorf
+description: Log ERROR and fail the build from the templates.
+date: 2017-09-30
+publishdate: 2017-09-30
+lastmod: 2017-09-30
+categories: [functions]
+menu:
+  docs:
+    parent: "functions"
+keywords: [strings, log, error]
+signature: ["errorf FORMAT INPUT"]
+workson: []
+hugoversion:
+relatedfuncs: [printf]
+deprecated: false
+aliases: []
+---
+
+`errorf` will evaluate a format string, then output the result to the ERROR log (and only once per error message to avoid flooding the log).
+
+This will also cause the build to fail (the `hugo` command will `exit -1`).
+
+```
+{{ errorf "Failed to handle page %q" .Path }}
+```
+
+Note that `errorf` supports all the formatting verbs of the [fmt](https://golang.org/pkg/fmt/) package.