servo: Merge #14508 - Rewrite determine_request_referrer() to explicitly limit it to the checks it can do (from servo:determine_request_referrer); r=jdm,frewsxcv

Checks for the Client value should reside in the script thread.

I also noted some other issues in this code.

Source-Repo: https://github.com/servo/servo
Source-Revision: 882d5512bb9aa7263864fb18d702c1efb6401914

UltraBlame original commit: bb6d259f6f5dc49a5ef21de8d9d8177f7ce59413

Author: marco-c

servo/components/net/fetch/methods.rs

@@ -250,6 +250,12 @@ use
 std
 :
 :
+mem
+;
+use
+std
+:
+:
 rc
 :
 :
@@ -1245,43 +1251,81 @@ referrer_policy
 /
 Step
 8
-if
-*
+{
+let
+mut
+referrer
+=
 request
 .
 referrer
 .
-borrow
+borrow_mut
 (
 )
-!
+;
+let
+referrer_url
 =
+match
+mem
+:
+:
+replace
+(
+&
+mut
+*
+referrer
 Referrer
 :
 :
 NoReferrer
+)
 {
-/
-/
-remove
 Referrer
-headers
-set
-in
-past
-redirects
-/
-preflights
+:
+:
+NoReferrer
+=
+>
+None
+Referrer
+:
+:
+Client
+=
+>
+{
 /
 /
+FIXME
+(
+#
+14507
+)
+:
+We
+should
+never
+get
 this
-stops
-the
-assertion
+value
+here
+;
+it
+should
+/
+/
+already
+have
+been
+handled
 in
-determine_request_referrer
-from
-failing
+the
+script
+thread
+.
 request
 .
 headers
@@ -1299,33 +1343,49 @@ RefererHeader
 (
 )
 ;
-let
-referrer_url
-=
-determine_request_referrer
+None
+}
+Referrer
+:
+:
+ReferrerUrl
 (
-&
-mut
-*
+url
+)
+=
+>
+{
 request
 .
 headers
 .
 borrow_mut
 (
 )
-referrer_policy
-request
 .
-referrer
-.
-borrow_mut
+remove
+:
+:
+<
+RefererHeader
+>
 (
 )
+;
+determine_request_referrer
+(
+&
+mut
+*
+request
 .
-take
+headers
+.
+borrow_mut
 (
 )
+referrer_policy
+url
 request
 .
 current_url
@@ -1336,25 +1396,31 @@ clone
 (
 )
 )
+}
+}
 ;
-*
-request
-.
-referrer
-.
-borrow_mut
+if
+let
+Some
 (
+referrer_url
 )
 =
+referrer_url
+{
+*
+referrer
+=
 Referrer
 :
 :
-from_url
+ReferrerUrl
 (
 referrer_url
 )
 ;
 }
+}
 /
 /
 Step