internal: add syn version of [try_][pin_]init! macros

Implement the `[try_][pin_]init!` derive macro using syn to simplify
parsing by not going through an additional declarative macro.
This not only simplifies the code by a lot, increasing maintainability
and making it easier to implement new features. But also improves the
user experience by improving the error messages one gets when giving
incorrect inputs to the macro.
For example, placing a `,` after `..Zeroable::zeroed()` is not allowed:

    use pin_init::*;

    #[derive(Zeroable)]
    struct Foo {
        a: usize,
        b: usize,
    }

    fn main() {
        let _ = init!(Foo {
            a: 0,
            ..Zeroable::zeroed(),
        });
    }

The declarative macro produces this error:

    error: no rules expected `,`
       |
    11 |       let _ = init!(Foo {
       |  _____________^
    12 | |         a: 0,
    13 | |         ..Zeroable::zeroed(),
    14 | |     });
       | |______^ no rules expected this token in macro call
       |
    note: while trying to match `)`
      --> src/macros.rs
       |
       |         @munch_fields($(..Zeroable::zeroed())? $(,)?),
       |                                                     ^
       = note: this error originates in the macro `$crate::__init_internal` which comes from the expansion of the macro `init` (in Nightly builds, run with -Z macro-backtrace for more info)

    error: no rules expected `,`
       |
    11 |       let _ = init!(Foo {
       |  _____________^
    12 | |         a: 0,
    13 | |         ..Zeroable::zeroed(),
    14 | |     });
       | |______^ no rules expected this token in macro call
       |
    note: while trying to match `)`
      --> src/macros.rs
       |
       |         @munch_fields(..Zeroable::zeroed() $(,)?),
       |                                                 ^
       = note: this error originates in the macro `$crate::__init_internal` which comes from the expansion of the macro `init` (in Nightly builds, run with -Z macro-backtrace for more info)

The syn version reduces this error to the much more manageable:

    error: unexpected token, expected `}`
       |
    12 |         ..Zeroable::zeroed(),
       |                             ^

This reimplementation is benefiting the most from syn, as can be seen in
this example. It declares a struct with a single generic, but then
supplies two type arguments in the initializer:

    use pin_init::*;

    struct Foo<T> {
        value: T,
    }
    fn main() {
        let _ = init!(Foo::<(), ()> {
            value <- (),
        });
    }

The declarative version emits the following unreadable mess of an error
(shortened for brevity of the commit message):

    error: struct literal body without path
      |
    7 |       let _ = init!(Foo::<(), ()> {
      |  _____________^
    8 | |         value <- (),
    9 | |     });
      | |______^
      |
      = note: this error originates in the macro `$crate::__init_internal` which comes from the expansion of the macro `init` (in Nightly builds, run with -Z macro-backtrace for more info)
    help: you might have forgotten to add the struct literal inside the block
     --> src/macros.rs
      |
      ~                 ::core::ptr::write($slot, $t { SomeStruct {
      |9                    $($acc)*
      ~                 } });
      |

<...40 lines skipped...>

    error[E0061]: this function takes 2 arguments but 3 arguments were supplied
      |
    7 |       let _ = init!(Foo::<(), ()> {
      |  _____________^
    8 | |         value <- (),
    9 | |     });
      | |______^ unexpected argument #3
      |
    note: function defined here
     --> $RUST/core/src/ptr/mod.rs
      |
      | pub const unsafe fn write<T>(dst: *mut T, src: T) {
      |                     ^^^^^
      = note: this error originates in the macro `$crate::__init_internal` which comes from the expansion of the macro `init` (in Nightly builds, run with -Z macro-backtrace for more info)

This error delightfully reduces to the simple and clear message:

    error[E0107]: struct takes 1 generic argument but 2 generic arguments were supplied
      |
    7 |     let _ = init!(Foo::<(), ()> {
      |                   ^^^     ---- help: remove the unnecessary generic argument
      |                   |
      |                   expected 1 generic argument
      |
    note: struct defined here, with 1 generic parameter: `T`
     --> tests/ui/compile-fail/init/wrong_generics2.rs:3:8
      |
    3 | struct Foo<T> {
      |        ^^^ -

The syn version is only enabled in the user-space version and disabled
in the kernel until syn becomes available there.

Signed-off-by: Benno Lossin <[email protected]>

internal/src/lib.rs

@@ -32,6 +32,8 @@ mod pinned_drop;
 #[cfg(kernel)]
 mod zeroable;
 
+#[cfg(not(kernel))]
+mod init;
 #[cfg(not(kernel))]
 #[path = "syn_pin_data.rs"]
 mod pin_data;
@@ -56,3 +58,55 @@ pub fn pinned_drop(args: TokenStream, input: TokenStream) -> TokenStream {
 pub fn derive_zeroable(input: TokenStream) -> TokenStream {
     zeroable::derive(input.into()).into()
 }
+
+#[cfg(not(kernel))]
+#[proc_macro]
+pub fn pin_init(input: TokenStream) -> TokenStream {
+    use syn::parse_macro_input;
+    init::init(
+        parse_macro_input!(input as init::InPlaceInitializer),
+        true,
+        true,
+    )
+    .unwrap_or_else(|e| e.into_compile_error())
+    .into()
+}
+
+#[cfg(not(kernel))]
+#[proc_macro]
+pub fn init(input: TokenStream) -> TokenStream {
+    use syn::parse_macro_input;
+    init::init(
+        parse_macro_input!(input as init::InPlaceInitializer),
+        true,
+        false,
+    )
+    .unwrap_or_else(|e| e.into_compile_error())
+    .into()
+}
+
+#[cfg(not(kernel))]
+#[proc_macro]
+pub fn try_pin_init(input: TokenStream) -> TokenStream {
+    use syn::parse_macro_input;
+    init::init(
+        parse_macro_input!(input as init::InPlaceInitializer),
+        false,
+        true,
+    )
+    .unwrap_or_else(|e| e.into_compile_error())
+    .into()
+}
+
+#[cfg(not(kernel))]
+#[proc_macro]
+pub fn try_init(input: TokenStream) -> TokenStream {
+    use syn::parse_macro_input;
+    init::init(
+        parse_macro_input!(input as init::InPlaceInitializer),
+        false,
+        false,
+    )
+    .unwrap_or_else(|e| e.into_compile_error())
+    .into()
+}

src/__internal.rs

@@ -287,3 +287,8 @@ unsafe impl<T: ?Sized> PinInit<T, ()> for AlwaysFail<T> {
         Err(())
     }
 }
+
+pub use ::pin_init_internal::init;
+pub use ::pin_init_internal::pin_init;
+pub use ::pin_init_internal::try_init;
+pub use ::pin_init_internal::try_pin_init;

src/lib.rs

@@ -723,9 +723,9 @@ macro_rules! pin_init {
     ($(&$this:ident in)? $t:ident $(::<$($generics:ty),* $(,)?>)? {
         $($fields:tt)*
     }) => {
-        $crate::try_pin_init!($(&$this in)? $t $(::<$($generics),*>)? {
+        $crate::__internal::pin_init!($(&$this in)? $t $(::<$($generics),*>)? {
             $($fields)*
-        }? ::core::convert::Infallible)
+        })
     };
 }
 
@@ -774,16 +774,9 @@ macro_rules! try_pin_init {
     ($(&$this:ident in)? $t:ident $(::<$($generics:ty),* $(,)?>)? {
         $($fields:tt)*
     }? $err:ty) => {
-        $crate::__init_internal!(
-            @this($($this)?),
-            @typ($t $(::<$($generics),*>)? ),
-            @fields($($fields)*),
-            @error($err),
-            @data(PinData, use_data),
-            @has_data(HasPinData, __pin_data),
-            @construct_closure(pin_init_from_closure),
-            @munch_fields($($fields)*),
-        )
+        $crate::__internal::try_pin_init!($(&$this in)? $t $(::<$($generics),*>)? {
+            $($fields)*
+        }? $err)
     }
 }
 
@@ -830,9 +823,9 @@ macro_rules! init {
     ($(&$this:ident in)? $t:ident $(::<$($generics:ty),* $(,)?>)? {
         $($fields:tt)*
     }) => {
-        $crate::try_init!($(&$this in)? $t $(::<$($generics),*>)? {
+        $crate::__internal::init!($(&$this in)? $t $(::<$($generics),*>)? {
             $($fields)*
-        }? ::core::convert::Infallible)
+        })
     }
 }
 
@@ -879,16 +872,9 @@ macro_rules! try_init {
     ($(&$this:ident in)? $t:ident $(::<$($generics:ty),* $(,)?>)? {
         $($fields:tt)*
     }? $err:ty) => {
-        $crate::__init_internal!(
-            @this($($this)?),
-            @typ($t $(::<$($generics),*>)?),
-            @fields($($fields)*),
-            @error($err),
-            @data(InitData, /*no use_data*/),
-            @has_data(HasInitData, __init_data),
-            @construct_closure(init_from_closure),
-            @munch_fields($($fields)*),
-        )
+        $crate::__internal::try_init!($(&$this in)? $t $(::<$($generics),*>)? {
+            $($fields)*
+        }? $err)
     }
 }
 

tests/ui/compile-fail/init/colon_instead_of_arrow.stderr

@@ -1,14 +1,13 @@
 error[E0308]: mismatched types
-  --> tests/ui/compile-fail/init/colon_instead_of_arrow.rs:21:9
+  --> tests/ui/compile-fail/init/colon_instead_of_arrow.rs:21:31
    |
 14 |     fn new() -> impl PinInit<Self> {
    |                 ------------------ the found opaque type
 ...
 21 |         pin_init!(Self { bar: Bar::new() })
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |         |
-   |         expected `Bar`, found opaque type
-   |         arguments to this function are incorrect
+   |                          ---  ^^^^^^^^^^ expected `Bar`, found opaque type
+   |                          |
+   |                          arguments to this function are incorrect
    |
    = note:   expected struct `Bar`
            found opaque type `impl pin_init::PinInit<Bar>`
@@ -17,4 +16,3 @@ note: function defined here
    |
    | pub const unsafe fn write<T>(dst: *mut T, src: T) {
    |                     ^^^^^
-   = note: this error originates in the macro `$crate::__init_internal` which comes from the expansion of the macro `pin_init` (in Nightly builds, run with -Z macro-backtrace for more info)

tests/ui/compile-fail/init/field_value_wrong_type.stderr

@@ -1,15 +1,13 @@
 error[E0308]: mismatched types
- --> tests/ui/compile-fail/init/field_value_wrong_type.rs:8:13
+ --> tests/ui/compile-fail/init/field_value_wrong_type.rs:8:28
   |
 8 |     let _ = init!(Foo { a: () });
-  |             ^^^^^^^^^^^^^^^^^^^^
-  |             |
-  |             expected `usize`, found `()`
-  |             arguments to this function are incorrect
+  |                         -  ^^ expected `usize`, found `()`
+  |                         |
+  |                         arguments to this function are incorrect
   |
 note: function defined here
  --> $RUST/core/src/ptr/mod.rs
   |
   | pub const unsafe fn write<T>(dst: *mut T, src: T) {
   |                     ^^^^^
-  = note: this error originates in the macro `$crate::__init_internal` which comes from the expansion of the macro `init` (in Nightly builds, run with -Z macro-backtrace for more info)

tests/ui/compile-fail/init/invalid_init.stderr

@@ -5,10 +5,7 @@ error[E0277]: the trait bound `impl pin_init::PinInit<Bar>: Init<Bar>` is not sa
    |  _____________^
 19 | |         bar <- Bar::new(),
 20 | |     });
-   | |      ^
-   | |      |
-   | |______the trait `Init<Bar>` is not implemented for `impl pin_init::PinInit<Bar>`
-   |        required by a bound introduced by this call
+   | |______^ the trait `Init<Bar>` is not implemented for `impl pin_init::PinInit<Bar>`
    |
    = help: the trait `Init<T, E>` is implemented for `ChainInit<I, F, T, E>`
-   = note: this error originates in the macro `$crate::__init_internal` which comes from the expansion of the macro `init` (in Nightly builds, run with -Z macro-backtrace for more info)
+   = note: this error originates in the macro `$crate::__internal::init` which comes from the expansion of the macro `init` (in Nightly builds, run with -Z macro-backtrace for more info)

tests/ui/compile-fail/init/missing_comma.stderr

@@ -1,23 +1,5 @@
-error: no rules expected `c`
+error: expected `,`
   --> tests/ui/compile-fail/init/missing_comma.rs:16:9
    |
 16 |         c: Bar,
-   |         ^ no rules expected this token in macro call
-   |
-note: while trying to match `,`
-  --> src/macros.rs
-   |
-   |         @munch_fields($field:ident $(: $val:expr)?, $($rest:tt)*),
-   |                                                   ^
-
-error: no rules expected `c`
-  --> tests/ui/compile-fail/init/missing_comma.rs:16:9
-   |
-16 |         c: Bar,
-   |         ^ no rules expected this token in macro call
-   |
-note: while trying to match `,`
-  --> src/macros.rs
-   |
-   |         @munch_fields($field:ident $(: $val:expr)?, $($rest:tt)*),
-   |                                                   ^
+   |         ^

tests/ui/compile-fail/init/missing_comma_with_zeroable.stderr

@@ -10,16 +10,12 @@ help: you can add the `dyn` keyword if you want a trait object
    |               ++++         +
 
 error[E0308]: mismatched types
-  --> tests/ui/compile-fail/init/missing_comma_with_zeroable.rs:11:13
+  --> tests/ui/compile-fail/init/missing_comma_with_zeroable.rs:12:12
    |
-11 |       let _ = init!(Foo {
-   |  _____________^
-12 | |         a: 0..Zeroable::zeroed()
-13 | |     });
-   | |      ^
-   | |      |
-   | |______expected `usize`, found `Range<{integer}>`
-   |        arguments to this function are incorrect
+12 |         a: 0..Zeroable::zeroed()
+   |         -  ^^^^^^^^^^^^^^^^^^^^^ expected `usize`, found `Range<{integer}>`
+   |         |
+   |         arguments to this function are incorrect
    |
    = note: expected type `usize`
             found struct `std::ops::Range<{integer}>`
@@ -28,7 +24,6 @@ note: function defined here
    |
    | pub const unsafe fn write<T>(dst: *mut T, src: T) {
    |                     ^^^^^
-   = note: this error originates in the macro `$crate::__init_internal` which comes from the expansion of the macro `init` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0063]: missing field `b` in initializer of `Foo`
   --> tests/ui/compile-fail/init/missing_comma_with_zeroable.rs:11:19

tests/ui/compile-fail/init/missing_pin_data.stderr

@@ -5,15 +5,16 @@ error[E0599]: no associated item named `__pin_data` found for struct `Foo` in th
   | ---------- associated item `__pin_data` not found for this struct
 ...
 9 |         pin_init!(Self { a: 42 })
-  |         ^^^^^^^^^^^^^^^^^^^^^^^^^ associated item not found in `Foo`
+  |         ^^^^^^^^^^^^^^^^^^^^^^^^^
+  |         |
+  |         associated item not found in `Foo`
   |
   = help: items from traits can only be used if the trait is implemented and in scope
   = note: the following trait defines an item `__pin_data`, perhaps you need to implement it:
           candidate #1: `HasPinData`
-  = note: this error originates in the macro `$crate::try_pin_init` which comes from the expansion of the macro `pin_init` (in Nightly builds, run with -Z macro-backtrace for more info)
+  = note: this error originates in the macro `$crate::__internal::pin_init` which comes from the expansion of the macro `pin_init` (in Nightly builds, run with -Z macro-backtrace for more info)
 help: there is an associated function `__init_data` with a similar name
  --> src/lib.rs
   |
-  -             @has_data(HasPinData, __pin_data),
-  +             @has_data(HasPinData, __init_data),
+  |         __init_data
   |

tests/ui/compile-fail/init/no_error_coercion.stderr

@@ -11,4 +11,4 @@ error[E0277]: `?` couldn't convert the error to `std::alloc::AllocError`
    |                        the trait `From<Infallible>` is not implemented for `std::alloc::AllocError`
    |
    = note: the question mark operation (`?`) implicitly performs a conversion on the error value using the `From` trait
-   = note: this error originates in the macro `$crate::__init_internal` which comes from the expansion of the macro `try_init` (in Nightly builds, run with -Z macro-backtrace for more info)
+   = note: this error originates in the macro `$crate::__internal::try_init` which comes from the expansion of the macro `try_init` (in Nightly builds, run with -Z macro-backtrace for more info)

tests/ui/compile-fail/init/wrong_generics2.stderr

@@ -1,51 +1,3 @@
-error: struct literal body without path
- --> tests/ui/compile-fail/init/wrong_generics2.rs:7:13
-  |
-7 |       let _ = init!(Foo::<(), ()> {
-  |  _____________^
-8 | |         value <- (),
-9 | |     });
-  | |______^
-  |
-  = note: this error originates in the macro `$crate::__init_internal` which comes from the expansion of the macro `init` (in Nightly builds, run with -Z macro-backtrace for more info)
-help: you might have forgotten to add the struct literal inside the block
- --> src/macros.rs
-  |
-  ~                 ::core::ptr::write($slot, $t { SomeStruct {
-  |9                    $($acc)*
-  ~                 } });
-  |
-
-error: expected one of `)`, `,`, `.`, `?`, or an operator, found `{`
- --> tests/ui/compile-fail/init/wrong_generics2.rs:7:13
-  |
-7 |       let _ = init!(Foo::<(), ()> {
-  |  _____________^
-8 | |         value <- (),
-9 | |     });
-  | |      ^
-  | |      |
-  | |______expected one of `)`, `,`, `.`, `?`, or an operator
-  |        help: missing `,`
-  |
-  = note: this error originates in the macro `$crate::__init_internal` which comes from the expansion of the macro `init` (in Nightly builds, run with -Z macro-backtrace for more info)
-
-error[E0423]: expected value, found struct `Foo`
- --> tests/ui/compile-fail/init/wrong_generics2.rs:7:13
-  |
-3 | / struct Foo<T> {
-4 | |     value: T,
-5 | | }
-  | |_- `Foo` defined here
-6 |   fn main() {
-7 |       let _ = init!(Foo::<(), ()> {
-  |  _____________^
-8 | |         value <- (),
-9 | |     });
-  | |______^ help: use struct literal syntax instead: `Foo { value: val }`
-  |
-  = note: this error originates in the macro `$crate::try_init` which comes from the expansion of the macro `init` (in Nightly builds, run with -Z macro-backtrace for more info)
-
 error[E0107]: struct takes 1 generic argument but 2 generic arguments were supplied
  --> tests/ui/compile-fail/init/wrong_generics2.rs:7:19
   |
@@ -59,19 +11,3 @@ note: struct defined here, with 1 generic parameter: `T`
   |
 3 | struct Foo<T> {
   |        ^^^ -
-
-error[E0061]: this function takes 2 arguments but 3 arguments were supplied
- --> tests/ui/compile-fail/init/wrong_generics2.rs:7:13
-  |
-7 |       let _ = init!(Foo::<(), ()> {
-  |  _____________^
-8 | |         value <- (),
-9 | |     });
-  | |______^ unexpected argument #3
-  |
-note: function defined here
- --> $RUST/core/src/ptr/mod.rs
-  |
-  | pub const unsafe fn write<T>(dst: *mut T, src: T) {
-  |                     ^^^^^
-  = note: this error originates in the macro `$crate::__init_internal` which comes from the expansion of the macro `init` (in Nightly builds, run with -Z macro-backtrace for more info)

tests/ui/compile-fail/zeroable/with_comma.rs

@@ -1,4 +1,3 @@
-extern crate pin_init;
 use pin_init::*;
 
 #[derive(Zeroable)]

tests/ui/compile-fail/zeroable/with_comma.stderr

@@ -1,33 +1,5 @@
-error: no rules expected `,`
-  --> tests/ui/compile-fail/zeroable/with_comma.rs:11:13
+error: unexpected token, expected `}`
+  --> tests/ui/compile-fail/zeroable/with_comma.rs:12:29
    |
-11 |       let _ = init!(Foo {
-   |  _____________^
-12 | |         a: 0,
-13 | |         ..Zeroable::zeroed(),
-14 | |     });
-   | |______^ no rules expected this token in macro call
-   |
-note: while trying to match `)`
-  --> src/macros.rs
-   |
-   |         @munch_fields($(..Zeroable::zeroed())? $(,)?),
-   |                                                     ^
-   = note: this error originates in the macro `$crate::__init_internal` which comes from the expansion of the macro `init` (in Nightly builds, run with -Z macro-backtrace for more info)
-
-error: no rules expected `,`
-  --> tests/ui/compile-fail/zeroable/with_comma.rs:11:13
-   |
-11 |       let _ = init!(Foo {
-   |  _____________^
-12 | |         a: 0,
-13 | |         ..Zeroable::zeroed(),
-14 | |     });
-   | |______^ no rules expected this token in macro call
-   |
-note: while trying to match `)`
-  --> src/macros.rs
-   |
-   |         @munch_fields(..Zeroable::zeroed() $(,)?),
-   |                                                 ^
-   = note: this error originates in the macro `$crate::__init_internal` which comes from the expansion of the macro `init` (in Nightly builds, run with -Z macro-backtrace for more info)
+12 |         ..Zeroable::zeroed(),
+   |                             ^