Simplify proc macro signature validity check

Cargo.lock

@@ -5139,6 +5139,7 @@ dependencies = [
  "rustc_session",
  "rustc_span",
  "rustc_target",
+ "rustc_trait_selection",
  "tracing",
 ]
 

compiler/rustc_passes/Cargo.toml

@@ -22,3 +22,4 @@ rustc_span = { path = "../rustc_span" }
 rustc_lexer = { path = "../rustc_lexer" }
 rustc_ast_pretty = { path = "../rustc_ast_pretty" }
 rustc_feature = { path = "../rustc_feature" }
+rustc_trait_selection = { path = "../rustc_trait_selection" }

compiler/rustc_passes/messages.ftl

@@ -720,26 +720,7 @@ passes_ignored_derived_impls =
      *[other] traits {$trait_list}, but these are
     } intentionally ignored during dead code analysis
 
-passes_proc_macro_typeerror = mismatched {$kind} signature
+passes_proc_macro_bad_sig = {$kind} has incorrect signature
-    .label = found {$found}, expected type `proc_macro::TokenStream`
-    .note = {$kind}s must have a signature of `{$expected_signature}`
-
-passes_proc_macro_diff_arg_count = mismatched {$kind} signature
-    .label = found unexpected {$count ->
-      [one] argument
-     *[other] arguments
-    }
-    .note = {$kind}s must have a signature of `{$expected_signature}`
-
-passes_proc_macro_missing_args = mismatched {$kind} signature
-    .label = {$kind} must have {$expected_input_count ->
-      [one] one argument
-     *[other] two arguments
-    } of type `proc_macro::TokenStream`
-
-passes_proc_macro_invalid_abi = proc macro functions may not be `extern "{$abi}"`
-
-passes_proc_macro_unsafe = proc macro functions may not be `unsafe`
 
 passes_skipping_const_checks = skipping const checks
 

compiler/rustc_passes/src/check_attr.rs

@@ -19,9 +19,10 @@
 use rustc_hir::{MethodKind, Target, Unsafety};
 use rustc_middle::hir::nested_filter;
 use rustc_middle::middle::resolve_bound_vars::ObjectLifetimeDefault;
-use rustc_middle::ty::fast_reject::{DeepRejectCtxt, TreatParams};
+use rustc_middle::traits::ObligationCause;
+use rustc_middle::ty::error::ExpectedFound;
 use rustc_middle::ty::query::Providers;
-use rustc_middle::ty::{ParamEnv, TyCtxt};
+use rustc_middle::ty::{self, TyCtxt};
 use rustc_session::lint::builtin::{
     CONFLICTING_REPR_HINTS, INVALID_DOC_ATTRIBUTES, INVALID_MACRO_EXPORT_ARGUMENTS,
     UNUSED_ATTRIBUTES,
@@ -30,6 +31,9 @@
 use rustc_span::symbol::{kw, sym, Symbol};
 use rustc_span::{Span, DUMMY_SP};
 use rustc_target::spec::abi::Abi;
+use rustc_trait_selection::infer::{TyCtxtInferExt, ValuePairs};
+use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt;
+use rustc_trait_selection::traits::ObligationCtxt;
 use std::cell::Cell;
 use std::collections::hash_map::Entry;
 
@@ -2188,101 +2192,67 @@ fn check_unused_attribute(&self, hir_id: HirId, attr: &Attribute) {
     ///
     /// If this best effort goes wrong, it will just emit a worse error later (see #102923)
     fn check_proc_macro(&self, hir_id: HirId, target: Target, kind: ProcMacroKind) {
-        let expected_input_count = match kind {
+        if target != Target::Fn {
-            ProcMacroKind::Attribute => 2,
+            return;
-            ProcMacroKind::Derive | ProcMacroKind::FunctionLike => 1,
+        }
-        };
-
-        let expected_signature = match kind {
-            ProcMacroKind::Attribute => "fn(TokenStream, TokenStream) -> TokenStream",
-            ProcMacroKind::Derive | ProcMacroKind::FunctionLike => "fn(TokenStream) -> TokenStream",
-        };
 
         let tcx = self.tcx;
-        if target == Target::Fn {
+        let Some(token_stream_def_id) = tcx.get_diagnostic_item(sym::TokenStream) else { return; };
-            let Some(tokenstream) = tcx.get_diagnostic_item(sym::TokenStream) else {return};
+        let Some(token_stream) = tcx.type_of(token_stream_def_id).no_bound_vars() else { return; };
-            let tokenstream = tcx.type_of(tokenstream).subst_identity();
 
-            let id = hir_id.expect_owner();
+        let def_id = hir_id.expect_owner().def_id;
-            let hir_sig = tcx.hir().fn_sig_by_hir_id(hir_id).unwrap();
+        let param_env = ty::ParamEnv::empty();
 
-            let sig =
+        let infcx = tcx.infer_ctxt().build();
-                tcx.liberate_late_bound_regions(id.to_def_id(), tcx.fn_sig(id).subst_identity());
+        let ocx = ObligationCtxt::new(&infcx);
-            let sig = tcx.normalize_erasing_regions(ParamEnv::empty(), sig);
 
-            // We don't currently require that the function signature is equal to
+        let span = tcx.def_span(def_id);
-            // `fn(TokenStream) -> TokenStream`, but instead monomorphizes to
+        let fresh_substs = infcx.fresh_substs_for_item(span, def_id.to_def_id());
-            // `fn(TokenStream) -> TokenStream` after some substitution of generic arguments.
+        let sig = tcx.liberate_late_bound_regions(
-            //
+            def_id.to_def_id(),
-            // Properly checking this means pulling in additional `rustc` crates, so we don't.
+            tcx.fn_sig(def_id).subst(tcx, fresh_substs),
-            let drcx = DeepRejectCtxt { treat_obligation_params: TreatParams::AsCandidateKey };
+        );
 
-            if sig.abi != Abi::Rust {
+        let cause = ObligationCause::misc(span, def_id);
-                tcx.sess.emit_err(errors::ProcMacroInvalidAbi {
+        let sig = ocx.normalize(&cause, param_env, sig);
-                    span: hir_sig.span,
+
-                    abi: sig.abi.name(),
+        // proc macro is not WF.
-                });
+        let errors = ocx.select_where_possible();
+        if !errors.is_empty() {
+            return;
+        }
+
+        let expected_sig = tcx.mk_fn_sig(
+            std::iter::repeat(token_stream).take(match kind {
+                ProcMacroKind::Attribute => 2,
+                ProcMacroKind::Derive | ProcMacroKind::FunctionLike => 1,
+            }),
+            token_stream,
+            false,
+            Unsafety::Normal,
+            Abi::Rust,
+        );
+
+        if let Err(terr) = ocx.eq(&cause, param_env, expected_sig, sig) {
+            let mut diag = tcx.sess.create_err(errors::ProcMacroBadSig { span, kind });
+            infcx.err_ctxt().note_type_err(
+                &mut diag,
+                &cause,
+                None,
+                Some(ValuePairs::Sigs(ExpectedFound { expected: expected_sig, found: sig })),
+                terr,
+                false,
+                false,
+            );
+            diag.emit();
             self.abort.set(true);
         }
 
-            if sig.unsafety == Unsafety::Unsafe {
+        let errors = ocx.select_all_or_error();
-                tcx.sess.emit_err(errors::ProcMacroUnsafe { span: hir_sig.span });
+        if !errors.is_empty() {
+            infcx.err_ctxt().report_fulfillment_errors(&errors);
             self.abort.set(true);
         }
-
-            let output = sig.output();
-
-            // Typecheck the output
-            if !drcx.types_may_unify(output, tokenstream) {
-                tcx.sess.emit_err(errors::ProcMacroTypeError {
-                    span: hir_sig.decl.output.span(),
-                    found: output,
-                    kind,
-                    expected_signature,
-                });
-                self.abort.set(true);
-            }
-
-            if sig.inputs().len() < expected_input_count {
-                tcx.sess.emit_err(errors::ProcMacroMissingArguments {
-                    expected_input_count,
-                    span: hir_sig.span,
-                    kind,
-                    expected_signature,
-                });
-                self.abort.set(true);
-            }
-
-            // Check that the inputs are correct, if there are enough.
-            if sig.inputs().len() >= expected_input_count {
-                for (arg, input) in
-                    sig.inputs().iter().zip(hir_sig.decl.inputs).take(expected_input_count)
-                {
-                    if !drcx.types_may_unify(*arg, tokenstream) {
-                        tcx.sess.emit_err(errors::ProcMacroTypeError {
-                            span: input.span,
-                            found: *arg,
-                            kind,
-                            expected_signature,
-                        });
-                        self.abort.set(true);
-                    }
-                }
-            }
-
-            // Check that there are not too many arguments
-            let body_id = tcx.hir().body_owned_by(id.def_id);
-            let excess = tcx.hir().body(body_id).params.get(expected_input_count..);
-            if let Some(excess @ [begin @ end] | excess @ [begin, .., end]) = excess {
-                tcx.sess.emit_err(errors::ProcMacroDiffArguments {
-                    span: begin.span.to(end.span),
-                    count: excess.len(),
-                    kind,
-                    expected_signature,
-                });
-                self.abort.set(true);
-            }
-        }
     }
 }
 

compiler/rustc_passes/src/errors.rs

@@ -1546,52 +1546,11 @@ pub struct ChangeFieldsToBeOfUnitType {
 }
 
 #[derive(Diagnostic)]
-#[diag(passes_proc_macro_typeerror)]
+#[diag(passes_proc_macro_bad_sig)]
-#[note]
+pub(crate) struct ProcMacroBadSig {
-pub(crate) struct ProcMacroTypeError<'tcx> {
     #[primary_span]
-    #[label]
     pub span: Span,
-    pub found: Ty<'tcx>,
     pub kind: ProcMacroKind,
-    pub expected_signature: &'static str,
-}
-
-#[derive(Diagnostic)]
-#[diag(passes_proc_macro_diff_arg_count)]
-pub(crate) struct ProcMacroDiffArguments {
-    #[primary_span]
-    #[label]
-    pub span: Span,
-    pub count: usize,
-    pub kind: ProcMacroKind,
-    pub expected_signature: &'static str,
-}
-
-#[derive(Diagnostic)]
-#[diag(passes_proc_macro_missing_args)]
-pub(crate) struct ProcMacroMissingArguments {
-    #[primary_span]
-    #[label]
-    pub span: Span,
-    pub expected_input_count: usize,
-    pub kind: ProcMacroKind,
-    pub expected_signature: &'static str,
-}
-
-#[derive(Diagnostic)]
-#[diag(passes_proc_macro_invalid_abi)]
-pub(crate) struct ProcMacroInvalidAbi {
-    #[primary_span]
-    pub span: Span,
-    pub abi: &'static str,
-}
-
-#[derive(Diagnostic)]
-#[diag(passes_proc_macro_unsafe)]
-pub(crate) struct ProcMacroUnsafe {
-    #[primary_span]
-    pub span: Span,
 }
 
 #[derive(Diagnostic)]

tests/ui/proc-macro/bad-projection.rs

@@ -0,0 +1,15 @@
+// force-host
+// no-prefer-dynamic
+
+#![crate_type = "proc-macro"]
+#![allow(warnings)]
+
+extern crate proc_macro;
+
+trait Project {
+    type Assoc;
+}
+
+#[proc_macro]
+pub fn uwu() -> <() as Project>::Assoc {}
+//~^ ERROR the trait bound `(): Project` is not satisfied

tests/ui/proc-macro/bad-projection.stderr

@@ -0,0 +1,9 @@
+error[E0277]: the trait bound `(): Project` is not satisfied
+  --> $DIR/bad-projection.rs:14:17
+   |
+LL | pub fn uwu() -> <() as Project>::Assoc {}
+   |                 ^^^^^^^^^^^^^^^^^^^^^^ the trait `Project` is not implemented for `()`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.

tests/ui/proc-macro/proc-macro-abi.rs

@@ -9,19 +9,19 @@
 
 #[proc_macro]
 pub extern "C" fn abi(a: TokenStream) -> TokenStream {
-    //~^ ERROR proc macro functions may not be `extern "C"`
+    //~^ ERROR function-like proc macro has incorrect signature
     a
 }
 
 #[proc_macro]
 pub extern "system" fn abi2(a: TokenStream) -> TokenStream {
-    //~^ ERROR proc macro functions may not be `extern "system"`
+    //~^ ERROR function-like proc macro has incorrect signature
     a
 }
 
 #[proc_macro]
 pub extern fn abi3(a: TokenStream) -> TokenStream {
-    //~^ ERROR proc macro functions may not be `extern "C"`
+    //~^ ERROR function-like proc macro has incorrect signature
     a
 }
 

tests/ui/proc-macro/proc-macro-abi.stderr

@@ -1,20 +1,29 @@
-error: proc macro functions may not be `extern "C"`
+error: function-like proc macro has incorrect signature
   --> $DIR/proc-macro-abi.rs:11:1
    |
 LL | pub extern "C" fn abi(a: TokenStream) -> TokenStream {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected "Rust" fn, found "C" fn
+   |
+   = note: expected signature `fn(proc_macro::TokenStream) -> proc_macro::TokenStream`
+              found signature `extern "C" fn(proc_macro::TokenStream) -> proc_macro::TokenStream`
 
-error: proc macro functions may not be `extern "system"`
+error: function-like proc macro has incorrect signature
   --> $DIR/proc-macro-abi.rs:17:1
    |
 LL | pub extern "system" fn abi2(a: TokenStream) -> TokenStream {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected "Rust" fn, found "system" fn
+   |
+   = note: expected signature `fn(proc_macro::TokenStream) -> proc_macro::TokenStream`
+              found signature `extern "system" fn(proc_macro::TokenStream) -> proc_macro::TokenStream`
 
-error: proc macro functions may not be `extern "C"`
+error: function-like proc macro has incorrect signature
   --> $DIR/proc-macro-abi.rs:23:1
    |
 LL | pub extern fn abi3(a: TokenStream) -> TokenStream {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected "Rust" fn, found "C" fn
+   |
+   = note: expected signature `fn(proc_macro::TokenStream) -> proc_macro::TokenStream`
+              found signature `extern "C" fn(proc_macro::TokenStream) -> proc_macro::TokenStream`
 
 error: aborting due to 3 previous errors
 

tests/ui/proc-macro/signature-proc-macro-attribute.rs

@@ -8,25 +8,23 @@
 
 #[proc_macro_attribute]
 pub fn bad_input(input: String) -> TokenStream {
-    //~^ ERROR mismatched attribute proc macro signature
+    //~^ ERROR attribute proc macro has incorrect signature
     ::proc_macro::TokenStream::new()
 }
 
 #[proc_macro_attribute]
 pub fn bad_output(input: TokenStream) -> String {
-    //~^ ERROR mismatched attribute proc macro signature
+    //~^ ERROR attribute proc macro has incorrect signature
-    //~| ERROR mismatched attribute proc macro signature
     String::from("blah")
 }
 
 #[proc_macro_attribute]
 pub fn bad_everything(input: String) -> String {
-    //~^ ERROR mismatched attribute proc macro signature
+    //~^ ERROR attribute proc macro has incorrect signature
-    //~| ERROR mismatched attribute proc macro signature
     input
 }
 
 #[proc_macro_attribute]
 pub fn too_many(a: TokenStream, b: TokenStream, c: String) -> TokenStream {
-    //~^ ERROR mismatched attribute proc macro signature
+    //~^ ERROR attribute proc macro has incorrect signature
 }

tests/ui/proc-macro/signature-proc-macro-attribute.stderr

@@ -1,42 +1,38 @@
-error: mismatched attribute proc macro signature
+error: attribute proc macro has incorrect signature
   --> $DIR/signature-proc-macro-attribute.rs:10:1
    |
 LL | pub fn bad_input(input: String) -> TokenStream {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ attribute proc macro must have two arguments of type `proc_macro::TokenStream`
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ incorrect number of function parameters
-
-error: mismatched attribute proc macro signature
-  --> $DIR/signature-proc-macro-attribute.rs:16:42
    |
-LL | pub fn bad_output(input: TokenStream) -> String {
+   = note: expected signature `fn(proc_macro::TokenStream, proc_macro::TokenStream) -> proc_macro::TokenStream`
-   |                                          ^^^^^^ found std::string::String, expected type `proc_macro::TokenStream`
+              found signature `fn(std::string::String) -> proc_macro::TokenStream`
-   |
-   = note: attribute proc macros must have a signature of `fn(TokenStream, TokenStream) -> TokenStream`
 
-error: mismatched attribute proc macro signature
+error: attribute proc macro has incorrect signature
   --> $DIR/signature-proc-macro-attribute.rs:16:1
    |
 LL | pub fn bad_output(input: TokenStream) -> String {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ attribute proc macro must have two arguments of type `proc_macro::TokenStream`
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ incorrect number of function parameters
+   |
+   = note: expected signature `fn(proc_macro::TokenStream, proc_macro::TokenStream) -> proc_macro::TokenStream`
+              found signature `fn(proc_macro::TokenStream) -> std::string::String`
 
-error: mismatched attribute proc macro signature
+error: attribute proc macro has incorrect signature
-  --> $DIR/signature-proc-macro-attribute.rs:23:41
+  --> $DIR/signature-proc-macro-attribute.rs:22:1
    |
 LL | pub fn bad_everything(input: String) -> String {
-   |                                         ^^^^^^ found std::string::String, expected type `proc_macro::TokenStream`
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ incorrect number of function parameters
    |
-   = note: attribute proc macros must have a signature of `fn(TokenStream, TokenStream) -> TokenStream`
+   = note: expected signature `fn(proc_macro::TokenStream, proc_macro::TokenStream) -> proc_macro::TokenStream`
+              found signature `fn(std::string::String) -> std::string::String`
 
-error: mismatched attribute proc macro signature
+error: attribute proc macro has incorrect signature
-  --> $DIR/signature-proc-macro-attribute.rs:23:1
+  --> $DIR/signature-proc-macro-attribute.rs:28:1
-   |
-LL | pub fn bad_everything(input: String) -> String {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ attribute proc macro must have two arguments of type `proc_macro::TokenStream`
-
-error: mismatched attribute proc macro signature
-  --> $DIR/signature-proc-macro-attribute.rs:30:49
    |
 LL | pub fn too_many(a: TokenStream, b: TokenStream, c: String) -> TokenStream {
-   |                                                 ^^^^^^^^^ found unexpected argument
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ incorrect number of function parameters
+   |
+   = note: expected signature `fn(proc_macro::TokenStream, proc_macro::TokenStream) -> proc_macro::TokenStream`
+              found signature `fn(proc_macro::TokenStream, proc_macro::TokenStream, std::string::String) -> proc_macro::TokenStream`
 
-error: aborting due to 6 previous errors
+error: aborting due to 4 previous errors
 

tests/ui/proc-macro/signature-proc-macro-derive.rs

@@ -8,24 +8,23 @@
 
 #[proc_macro_derive(Blah)]
 pub fn bad_input(input: String) -> TokenStream {
-    //~^ ERROR mismatched derive proc macro signature
+    //~^ ERROR derive proc macro has incorrect signature
     TokenStream::new()
 }
 
 #[proc_macro_derive(Bleh)]
 pub fn bad_output(input: TokenStream) -> String {
-    //~^ ERROR mismatched derive proc macro signature
+    //~^ ERROR derive proc macro has incorrect signature
     String::from("blah")
 }
 
 #[proc_macro_derive(Bluh)]
 pub fn bad_everything(input: String) -> String {
-    //~^ ERROR mismatched derive proc macro signature
+    //~^ ERROR derive proc macro has incorrect signature
-    //~| ERROR mismatched derive proc macro signature
     input
 }
 
 #[proc_macro_derive(Blih)]
 pub fn too_many(a: TokenStream, b: TokenStream, c: String) -> TokenStream {
-    //~^ ERROR mismatched derive proc macro signature
+    //~^ ERROR derive proc macro has incorrect signature
 }

tests/ui/proc-macro/signature-proc-macro-derive.stderr

@@ -1,40 +1,38 @@
-error: mismatched derive proc macro signature
+error: derive proc macro has incorrect signature
-  --> $DIR/signature-proc-macro-derive.rs:10:25
+  --> $DIR/signature-proc-macro-derive.rs:10:1
    |
 LL | pub fn bad_input(input: String) -> TokenStream {
-   |                         ^^^^^^ found std::string::String, expected type `proc_macro::TokenStream`
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `proc_macro::TokenStream`, found `std::string::String`
    |
-   = note: derive proc macros must have a signature of `fn(TokenStream) -> TokenStream`
+   = note: expected signature `fn(proc_macro::TokenStream) -> proc_macro::TokenStream`
+              found signature `fn(std::string::String) -> proc_macro::TokenStream`
 
-error: mismatched derive proc macro signature
+error: derive proc macro has incorrect signature
-  --> $DIR/signature-proc-macro-derive.rs:16:42
+  --> $DIR/signature-proc-macro-derive.rs:16:1
    |
 LL | pub fn bad_output(input: TokenStream) -> String {
-   |                                          ^^^^^^ found std::string::String, expected type `proc_macro::TokenStream`
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `proc_macro::TokenStream`, found `std::string::String`
    |
-   = note: derive proc macros must have a signature of `fn(TokenStream) -> TokenStream`
+   = note: expected signature `fn(proc_macro::TokenStream) -> proc_macro::TokenStream`
+              found signature `fn(proc_macro::TokenStream) -> std::string::String`
 
-error: mismatched derive proc macro signature
+error: derive proc macro has incorrect signature
-  --> $DIR/signature-proc-macro-derive.rs:22:41
+  --> $DIR/signature-proc-macro-derive.rs:22:1
    |
 LL | pub fn bad_everything(input: String) -> String {
-   |                                         ^^^^^^ found std::string::String, expected type `proc_macro::TokenStream`
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `proc_macro::TokenStream`, found `std::string::String`
    |
-   = note: derive proc macros must have a signature of `fn(TokenStream) -> TokenStream`
+   = note: expected signature `fn(proc_macro::TokenStream) -> proc_macro::TokenStream`
+              found signature `fn(std::string::String) -> std::string::String`
 
-error: mismatched derive proc macro signature
+error: derive proc macro has incorrect signature
-  --> $DIR/signature-proc-macro-derive.rs:22:30
+  --> $DIR/signature-proc-macro-derive.rs:28:1
-   |
-LL | pub fn bad_everything(input: String) -> String {
-   |                              ^^^^^^ found std::string::String, expected type `proc_macro::TokenStream`
-   |
-   = note: derive proc macros must have a signature of `fn(TokenStream) -> TokenStream`
-
-error: mismatched derive proc macro signature
-  --> $DIR/signature-proc-macro-derive.rs:29:33
    |
 LL | pub fn too_many(a: TokenStream, b: TokenStream, c: String) -> TokenStream {
-   |                                 ^^^^^^^^^^^^^^^^^^^^^^^^^ found unexpected arguments
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ incorrect number of function parameters
+   |
+   = note: expected signature `fn(proc_macro::TokenStream) -> proc_macro::TokenStream`
+              found signature `fn(proc_macro::TokenStream, proc_macro::TokenStream, std::string::String) -> proc_macro::TokenStream`
 
-error: aborting due to 5 previous errors
+error: aborting due to 4 previous errors
 

tests/ui/proc-macro/signature-proc-macro.rs

@@ -8,24 +8,23 @@
 
 #[proc_macro]
 pub fn bad_input(input: String) -> TokenStream {
-    //~^ ERROR mismatched function-like proc macro signature
+    //~^ ERROR function-like proc macro has incorrect signature
     ::proc_macro::TokenStream::new()
 }
 
 #[proc_macro]
 pub fn bad_output(input: TokenStream) -> String {
-    //~^ ERROR mismatched function-like proc macro signature
+    //~^ ERROR function-like proc macro has incorrect signature
     String::from("blah")
 }
 
 #[proc_macro]
 pub fn bad_everything(input: String) -> String {
-    //~^ ERROR mismatched function-like proc macro signature
+    //~^ ERROR function-like proc macro has incorrect signature
-    //~| ERROR mismatched function-like proc macro signature
     input
 }
 
 #[proc_macro]
 pub fn too_many(a: TokenStream, b: TokenStream, c: String) -> TokenStream {
-    //~^ ERROR mismatched function-like proc macro signature
+    //~^ ERROR function-like proc macro has incorrect signature
 }

tests/ui/proc-macro/signature-proc-macro.stderr

@@ -1,40 +1,38 @@
-error: mismatched function-like proc macro signature
+error: function-like proc macro has incorrect signature
-  --> $DIR/signature-proc-macro.rs:10:25
+  --> $DIR/signature-proc-macro.rs:10:1
    |
 LL | pub fn bad_input(input: String) -> TokenStream {
-   |                         ^^^^^^ found std::string::String, expected type `proc_macro::TokenStream`
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `proc_macro::TokenStream`, found `std::string::String`
    |
-   = note: function-like proc macros must have a signature of `fn(TokenStream) -> TokenStream`
+   = note: expected signature `fn(proc_macro::TokenStream) -> proc_macro::TokenStream`
+              found signature `fn(std::string::String) -> proc_macro::TokenStream`
 
-error: mismatched function-like proc macro signature
+error: function-like proc macro has incorrect signature
-  --> $DIR/signature-proc-macro.rs:16:42
+  --> $DIR/signature-proc-macro.rs:16:1
    |
 LL | pub fn bad_output(input: TokenStream) -> String {
-   |                                          ^^^^^^ found std::string::String, expected type `proc_macro::TokenStream`
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `proc_macro::TokenStream`, found `std::string::String`
    |
-   = note: function-like proc macros must have a signature of `fn(TokenStream) -> TokenStream`
+   = note: expected signature `fn(proc_macro::TokenStream) -> proc_macro::TokenStream`
+              found signature `fn(proc_macro::TokenStream) -> std::string::String`
 
-error: mismatched function-like proc macro signature
+error: function-like proc macro has incorrect signature
-  --> $DIR/signature-proc-macro.rs:22:41
+  --> $DIR/signature-proc-macro.rs:22:1
    |
 LL | pub fn bad_everything(input: String) -> String {
-   |                                         ^^^^^^ found std::string::String, expected type `proc_macro::TokenStream`
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `proc_macro::TokenStream`, found `std::string::String`
    |
-   = note: function-like proc macros must have a signature of `fn(TokenStream) -> TokenStream`
+   = note: expected signature `fn(proc_macro::TokenStream) -> proc_macro::TokenStream`
+              found signature `fn(std::string::String) -> std::string::String`
 
-error: mismatched function-like proc macro signature
+error: function-like proc macro has incorrect signature
-  --> $DIR/signature-proc-macro.rs:22:30
+  --> $DIR/signature-proc-macro.rs:28:1
-   |
-LL | pub fn bad_everything(input: String) -> String {
-   |                              ^^^^^^ found std::string::String, expected type `proc_macro::TokenStream`
-   |
-   = note: function-like proc macros must have a signature of `fn(TokenStream) -> TokenStream`
-
-error: mismatched function-like proc macro signature
-  --> $DIR/signature-proc-macro.rs:29:33
    |
 LL | pub fn too_many(a: TokenStream, b: TokenStream, c: String) -> TokenStream {
-   |                                 ^^^^^^^^^^^^^^^^^^^^^^^^^ found unexpected arguments
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ incorrect number of function parameters
+   |
+   = note: expected signature `fn(proc_macro::TokenStream) -> proc_macro::TokenStream`
+              found signature `fn(proc_macro::TokenStream, proc_macro::TokenStream, std::string::String) -> proc_macro::TokenStream`
 
-error: aborting due to 5 previous errors
+error: aborting due to 4 previous errors
 

tests/ui/proc-macro/signature.rs

@@ -8,10 +8,6 @@
 
 #[proc_macro_derive(A)]
 pub unsafe extern "C" fn foo(a: i32, b: u32) -> u32 {
-    //~^ ERROR: mismatched derive proc macro signature
+    //~^ ERROR: derive proc macro has incorrect signature
-    //~| mismatched derive proc macro signature
-    //~| mismatched derive proc macro signature
-    //~| proc macro functions may not be `extern
-    //~| proc macro functions may not be `unsafe
     loop {}
 }

tests/ui/proc-macro/signature.stderr

@@ -1,36 +1,11 @@
-error: proc macro functions may not be `extern "C"`
+error: derive proc macro has incorrect signature
   --> $DIR/signature.rs:10:1
    |
 LL | pub unsafe extern "C" fn foo(a: i32, b: u32) -> u32 {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected normal fn, found unsafe fn
-
-error: proc macro functions may not be `unsafe`
-  --> $DIR/signature.rs:10:1
    |
-LL | pub unsafe extern "C" fn foo(a: i32, b: u32) -> u32 {
+   = note: expected signature `fn(proc_macro::TokenStream) -> proc_macro::TokenStream`
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+              found signature `unsafe extern "C" fn(i32, u32) -> u32`
 
-error: mismatched derive proc macro signature
+error: aborting due to previous error
-  --> $DIR/signature.rs:10:49
-   |
-LL | pub unsafe extern "C" fn foo(a: i32, b: u32) -> u32 {
-   |                                                 ^^^ found u32, expected type `proc_macro::TokenStream`
-   |
-   = note: derive proc macros must have a signature of `fn(TokenStream) -> TokenStream`
-
-error: mismatched derive proc macro signature
-  --> $DIR/signature.rs:10:33
-   |
-LL | pub unsafe extern "C" fn foo(a: i32, b: u32) -> u32 {
-   |                                 ^^^ found i32, expected type `proc_macro::TokenStream`
-   |
-   = note: derive proc macros must have a signature of `fn(TokenStream) -> TokenStream`
-
-error: mismatched derive proc macro signature
-  --> $DIR/signature.rs:10:38
-   |
-LL | pub unsafe extern "C" fn foo(a: i32, b: u32) -> u32 {
-   |                                      ^^^^^^ found unexpected argument
-
-error: aborting due to 5 previous errors