Break up `__pin_project_internal`

[nnethercote]

I have been investigating expensive declarative macros recently. pin_project_lite::pin_project showed up as expensive for the futures-lite crate. This macro is very large, with 47 rules, many of these being internal rules. I thought that splitting it up into lots of smaller macros might help with performance. It only made a small (2%) performance improvement, but I think it increases readability enough that it's worth doing anyway. So I made this pull request.

[nnethercote]

It improves performance because it avoids lots of rule matching attempts that cannot succeed.

[nnethercote]

I just upgraded to the latest Nightly and ran cargo +nightly --all --all-features. For the ui tests I got lots of messages about expected output vs actual output, but no test failures. Those were just marked as wip... "work in progress"??

That command also changed lots of .stderr files, which was unexpected. A lot of the changes are due to the macro name changes, e.g.:

-  = note: this error originates in the macro `$crate::__pin_project_internal` (in Nightly builds, run with -Z macro-backtrace for more info)
+  = note: this error originates in the macro `$crate::__pin_project_make_drop_impl` (in Nightly builds, run with -Z macro-backtrace for more info)

but there are also some like this, which I don't understand:

-error: no rules expected the token `[`
- --> tests/ui/pin_project/invalid-bounds.rs:3:1
+error: no rules expected the token `:`
+ --> tests/ui/pin_project/invalid-bounds.rs:4:33
   |
-3 | / pin_project! {
-4 | |     struct Generics1<T: 'static : Sized> { //~ ERROR no rules expected the token `:`
-5 | |         field: T,
-6 | |     }
-7 | | }
-  | |_^ no rules expected this token in macro call
-  |
-  = note: this error originates in the macro `$crate::__pin_project_internal` (in Nightly builds, run with -Z macro-backtrace for more info)
+4 |     struct Generics1<T: 'static : Sized> { //~ ERROR no rules expected the token `:`
+  |                                 ^ no rules expected this token in macro call

[taiki-e]

For the ui tests I got lots of messages about expected output vs actual output, but no test failures.

Locally, ui test output is blessed by default.

but there are also some like this, which I don't understand:

The new diagnosis seems correct. I guess the rule reordering or rule separation may have changed the tokens that are considered expected to be matched first.

[bors[bot]]

Build succeeded:

• ci

[nnethercote]

Thanks!

[taiki-e]

Published in 0.2.9.