add the batching frontend

Author: ZuseZ4

compiler/rustc_ast/src/expand/autodiff_attrs.rs

@@ -77,6 +77,7 @@ pub struct AutoDiffAttrs {
     /// e.g. in the [JAX
     /// Documentation](https://jax.readthedocs.io/en/latest/_tutorials/advanced-autodiff.html#how-it-s-made-two-foundational-autodiff-functions).
     pub mode: DiffMode,
+    pub width: u32,
     pub ret_activity: DiffActivity,
     pub input_activity: Vec<DiffActivity>,
 }
@@ -222,13 +223,15 @@ impl AutoDiffAttrs {
     pub const fn error() -> Self {
         AutoDiffAttrs {
             mode: DiffMode::Error,
+            width: 0,
             ret_activity: DiffActivity::None,
             input_activity: Vec::new(),
         }
     }
     pub fn source() -> Self {
         AutoDiffAttrs {
             mode: DiffMode::Source,
+            width: 0,
             ret_activity: DiffActivity::None,
             input_activity: Vec::new(),
         }

compiler/rustc_builtin_macros/messages.ftl

@@ -79,6 +79,7 @@ builtin_macros_autodiff_ret_activity = invalid return activity {$act} in {$mode}
 builtin_macros_autodiff_ty_activity = {$act} can not be used for this type
 builtin_macros_autodiff_unknown_activity = did not recognize Activity: `{$act}`
 
+builtin_macros_autodiff_width = autodiff width must fit u32, but is {$width}
 builtin_macros_bad_derive_target = `derive` may only be applied to `struct`s, `enum`s and `union`s
     .label = not applicable here
     .label2 = not a `struct`, `enum` or `union`