Make Hugo Deploy respect custom MediaType/OutputFormat

[virgofx]

config.xml

[outputs]
  home = ["HTML", "RSS", "WEBMANIFEST"]
[mediaTypes."application/manifest+json"]
  suffixes = ["webmanifest"]
[outputFormats.webmanifest]
  name = "webmanifest"
  baseName = "site"
  mediaType = "application/manifest+json"
  rel = "manifest"

layouts/home.webmanifest

---

1. hugo build ✓

2. Confirm: ./public/site.webmanifest ✓

3. Curl Check ✓

   curl -I localhost:3000/site.webmanifest
   HTTP/1.1 200 OK
   Accept-Ranges: bytes
   Content-Length: 1202
   Content-Type: application/manifest+json; charset=utf-8
   Last-Modified: Fri, 07 Feb 2020 04:07:27 GMT
   Date: Fri, 07 Feb 2020 04:18:13 GMT
   

   Hugo dev server is serving file with appropriate content type ✓

4. Now lets deploy ....

   yarn deploy
   ...
   Uploading site.webmanifest (501 B, Content-Encoding: "gzip"): not found at target...
   

   X Confirmed the content type on server is: "application/x-gzip"

What version of Hugo are you using (hugo version)?

$ hugo version
Hugo Static Site Generator v0.63.2-934EE21F/extended linux/amd64 BuildDate: 2020-01-27T12:20:42Z

Does this issue reproduce with the latest release?

Yes

[virgofx]

Side note and maybe related --- I'm noting my XML files are set as application/xml and served that way locally via Hugo dev server; however, when deployed, they're converted to text/xml. So just seems the deploy is getting content-types from somewhere else maybe?

---

Edit/Answer: See below comment. It's falling back to TypeByExtension

[virgofx]

Checked the code ... there's a TODO to incorporate the MediaTypes just as I suspected. It must be done already in the dev server but is currently being skipped and jumping to TypeByExtension.
https://github.com/gohugoio/hugo/blob/master/deploy/deploy.go#L408-L410

Workaround
Use the custom matcher ContentType to specify an explicit content type.
(Note: This isn't in any of the documentation. Would be nice to have that in the docs instead of searching the code.)

[github-actions]

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