Bug 1613517 - Make rust generate better code for derive(Animate) and …

…derive(ComputeSquaredDistance). r=heycam

See rust-lang/rust#68867.

This technically changes the semantics of #[animate(fallback)] and such when
combined with #[animate(error)]. But no such combination exists and the new
semantics are perfectly reasonable as well, IMHO.

Differential Revision: https://phabricator.services.mozilla.com/D61761

UltraBlame original commit: bd4711d31ec6ab173b77406cb4ede0fa7a484af3

servo/components/style/values/animated/mod.rs

@@ -883,9 +883,9 @@ corresponding
 /
 match
 arm
-is
-not
-generated
+returns
+an
+error
 .
 /
 /

servo/components/style/values/distance.rs

@@ -195,9 +195,9 @@ corresponding
 /
 match
 arm
-is
-not
-generated
+returns
+an
+error
 .
 /
 /

servo/components/style_derive/animate.rs

@@ -133,6 +133,23 @@ input
 )
 ;
 let
+input_attrs
+=
+cg
+:
+:
+parse_input_attrs
+:
+:
+<
+AnimateInputAttrs
+>
+(
+&
+input
+)
+;
+let
 no_bound
 =
 animation_input_attrs
@@ -225,7 +242,7 @@ let
 (
 mut
 match_body
-append_error_clause
+needs_catchall_branch
 )
 =
 {
@@ -242,8 +259,7 @@ input
 )
 ;
 let
-mut
-append_error_clause
+needs_catchall_branch
 =
 s
 .
@@ -284,39 +300,13 @@ variant
 let
 arm
 =
-match
 derive_variant_arm
 (
 variant
 &
 mut
 where_clause
 )
-{
-Ok
-(
-arm
-)
-=
->
-arm
-Err
-(
-(
-)
-)
-=
->
-{
-append_error_clause
-=
-true
-;
-return
-body
-;
-}
-}
 ;
 quote
 !
@@ -331,7 +321,7 @@ arm
 ;
 (
 match_body
-append_error_clause
+needs_catchall_branch
 )
 }
 ;
@@ -344,82 +334,59 @@ where_clause
 where_clause
 ;
 if
-append_error_clause
+needs_catchall_branch
 {
-let
-input_attrs
-=
-cg
-:
-:
-parse_input_attrs
-:
+/
+/
+This
+ideally
+shouldn
+'
+t
+be
+needed
+but
+see
+/
+/
+https
 :
-<
-AnimateInputAttrs
->
-(
-&
-input
-)
-;
-if
-let
-Some
-(
-fallback
-)
-=
-input_attrs
+/
+/
+github
 .
-fallback
-{
+com
+/
+rust
+-
+lang
+/
+rust
+/
+issues
+/
+68867
 match_body
 .
 append_all
 (
 quote
 !
 {
-(
-this
-other
-)
+_
 =
 >
-#
-fallback
-(
-this
-other
-procedure
-)
-}
-)
-;
-}
-else
+unsafe
 {
-match_body
-.
-append_all
-(
-quote
+debug_unreachable
 !
-{
-_
-=
->
-Err
-(
 (
 )
-)
+}
 }
 )
 ;
 }
-}
 let
 name
 =
@@ -443,6 +410,45 @@ split_for_impl
 (
 )
 ;
+let
+fallback
+=
+match
+input_attrs
+.
+fallback
+{
+Some
+(
+fallback
+)
+=
+>
+quote
+!
+{
+#
+fallback
+(
+self
+other
+procedure
+)
+}
+None
+=
+>
+quote
+!
+{
+Err
+(
+(
+)
+)
+}
+}
+;
 quote
 !
 {
@@ -510,6 +516,35 @@ Self
 )
 >
 {
+if
+std
+:
+:
+mem
+:
+:
+discriminant
+(
+self
+)
+!
+=
+std
+:
+:
+mem
+:
+:
+discriminant
+(
+other
+)
+{
+return
+#
+fallback
+;
+}
 match
 (
 self
@@ -541,12 +576,7 @@ WhereClause
 )
 -
 >
-Result
-<
 TokenStream
-(
-)
->
 {
 let
 variant_attrs
@@ -569,19 +599,6 @@ ast
 )
 )
 ;
-if
-variant_attrs
-.
-error
-{
-return
-Err
-(
-(
-)
-)
-;
-}
 let
 (
 this_pattern
@@ -618,6 +635,33 @@ other
 "
 )
 ;
+if
+variant_attrs
+.
+error
+{
+return
+quote
+!
+{
+(
+&
+#
+this_pattern
+&
+#
+other_pattern
+)
+=
+>
+Err
+(
+(
+)
+)
+}
+;
+}
 let
 (
 result_value
@@ -833,8 +877,6 @@ procedure
 )
 )
 ;
-Ok
-(
 quote
 !
 {
@@ -858,7 +900,6 @@ result_value
 )
 }
 }
-)
 }
 #
 [