add rust error for activity to arg count missmatch (#111)

Author: ZuseZ4

compiler/rustc_builtin_macros/messages.ftl

@@ -5,6 +5,7 @@ builtin_macros_autodiff_unknown_activity = did not recognize activity {$act}
 builtin_macros_autodiff = autodiff must be applied to function
 builtin_macros_autodiff_not_build = this rustc version does not support autodiff
 builtin_macros_autodiff_mode_activity = {$act} can not be used in {$mode} Mode
+builtin_macros_autodiff_number_activities = expected {$expected} activities, but found {$found}
 builtin_macros_autodiff_mode = unknown Mode: `{$mode}`. Use `Forward` or `Reverse`
 builtin_macros_autodiff_ty_activity = {$act} can not be used for this type
 

compiler/rustc_builtin_macros/src/autodiff.rs

@@ -493,6 +493,15 @@ fn gen_enzyme_decl(
     x: &AutoDiffAttrs,
     span: Span,
 ) -> (ast::FnSig, Vec<String>, Vec<Ident>) {
+    let sig_args = sig.decl.inputs.len() + if sig.decl.output.has_ret() { 1 } else { 0 };
+    let num_activities = x.input_activity.len() + if x.has_ret_activity() { 1 } else { 0 };
+    if sig_args != num_activities {
+        ecx.sess.dcx().emit_fatal(errors::AutoDiffInvalidNumberActivities {
+            span,
+            expected: sig_args,
+            found: num_activities,
+        });
+    }
     assert!(sig.decl.inputs.len() == x.input_activity.len());
     assert!(sig.decl.output.has_ret() == x.has_ret_activity());
     let mut d_decl = sig.decl.clone();

compiler/rustc_builtin_macros/src/errors.rs

@@ -177,7 +177,14 @@ pub(crate) struct AutoDiffInvalidTypeForActivity {
     pub(crate) span: Span,
     pub(crate) act: String,
 }
-
+#[derive(Diagnostic)]
+#[diag(builtin_macros_autodiff_number_activities)]
+pub(crate) struct AutoDiffInvalidNumberActivities {
+    #[primary_span]
+    pub(crate) span: Span,
+    pub(crate) expected: usize,
+    pub(crate) found: usize,
+}
 #[derive(Diagnostic)]
 #[diag(builtin_macros_autodiff_mode_activity)]
 pub(crate) struct AutoDiffInvalidApplicationModeAct {