Implement method signature suggestion for trait mismatches error

Author: reddevilmidzy

compiler/rustc_hir_analysis/src/check/compare_impl_item.rs

@@ -18,7 +18,7 @@ use rustc_middle::ty::{
     TypeSuperFoldable, TypeVisitable, TypeVisitableExt, TypeVisitor, TypingMode, Upcast,
 };
 use rustc_middle::{bug, span_bug};
-use rustc_span::{DUMMY_SP, Span};
+use rustc_span::{BytePos, DUMMY_SP, Span};
 use rustc_trait_selection::error_reporting::InferCtxtErrorExt;
 use rustc_trait_selection::infer::InferCtxtExt;
 use rustc_trait_selection::regions::InferCtxtRegionExt;
@@ -1742,6 +1742,64 @@ fn compare_number_of_method_arguments<'tcx>(
             ),
         );
 
+        let sm = tcx.sess.source_map();
+        let find_param_bounds = |snippet: &str| -> Option<(usize, usize)> {
+            let start = snippet.find('(')?;
+            let mut depth = 1usize;
+            let bytes = snippet.as_bytes();
+            let mut i = start + 1;
+            while i < bytes.len() {
+                match bytes[i] as char {
+                    '(' => depth += 1,
+                    ')' => {
+                        depth -= 1;
+                        if depth == 0 {
+                            return Some((start + 1, i));
+                        }
+                    }
+                    _ => {}
+                }
+                i += 1;
+            }
+            None
+        };
+
+        let impl_inputs_span = (!impl_m_sig.span.is_dummy())
+            .then(|| {
+                sm.span_to_snippet(impl_m_sig.span).ok().and_then(|snippet| {
+                    find_param_bounds(&snippet).map(|(lo_rel, hi_rel)| {
+                        let lo = impl_m_sig.span.lo() + BytePos(lo_rel as u32);
+                        let hi = impl_m_sig.span.lo() + BytePos(hi_rel as u32);
+                        impl_m_sig.span.with_lo(lo).with_hi(hi)
+                    })
+                })
+            })
+            .flatten();
+
+        let suggestion = trait_m
+            .def_id
+            .as_local()
+            .and_then(|def_id| {
+                let (trait_sig, _) = tcx.hir_expect_trait_item(def_id).expect_fn();
+                sm.span_to_snippet(trait_sig.span).ok().and_then(|snippet| {
+                    find_param_bounds(&snippet)
+                        .map(|(lo_rel, hi_rel)| snippet[lo_rel..hi_rel].to_string())
+                })
+            })
+            .or_else(|| {
+                let signature = trait_m.signature(tcx);
+                find_param_bounds(&signature).map(|(lo, hi)| signature[lo..hi].trim().to_string())
+            });
+
+        if let (Some(span), Some(suggestion)) = (impl_inputs_span, suggestion) {
+            err.span_suggestion_verbose(
+                span,
+                "modify the signature to match the trait definition",
+                suggestion,
+                Applicability::MaybeIncorrect,
+            );
+        }
+
         return Err(err.emit_unless_delay(delay));
     }
 

tests/ui/error-codes/E0050.stderr

@@ -6,6 +6,11 @@ LL |     fn foo(&self, x: u8) -> bool;
 ...
 LL |     fn foo(&self) -> bool { true }
    |            ^^^^^ expected 2 parameters, found 1
+   |
+help: modify the signature to match the trait definition
+   |
+LL |     fn foo(&self, x: u8) -> bool { true }
+   |                 +++++++
 
 error[E0050]: method `bar` has 1 parameter but the declaration in trait `Foo::bar` has 4
   --> $DIR/E0050.rs:11:12
@@ -15,6 +20,11 @@ LL |     fn bar(&self, x: u8, y: u8, z: u8);
 ...
 LL |     fn bar(&self) { }
    |            ^^^^^ expected 4 parameters, found 1
+   |
+help: modify the signature to match the trait definition
+   |
+LL |     fn bar(&self, x: u8, y: u8, z: u8) { }
+   |                 +++++++++++++++++++++
 
 error[E0050]: method `less` has 4 parameters but the declaration in trait `Foo::less` has 1
   --> $DIR/E0050.rs:12:13
@@ -24,6 +34,12 @@ LL |     fn less(&self);
 ...
 LL |     fn less(&self, x: u8, y: u8, z: u8) { }
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^ expected 1 parameter, found 4
+   |
+help: modify the signature to match the trait definition
+   |
+LL -     fn less(&self, x: u8, y: u8, z: u8) { }
+LL +     fn less(&self) { }
+   |
 
 error: aborting due to 3 previous errors
 

tests/ui/impl-trait/in-trait/method-signature-matches.too_few.stderr

@@ -6,6 +6,11 @@ LL |     fn come_on_a_little_more_effort(_: (), _: (), _: ()) -> impl Sized;
 ...
 LL |     fn come_on_a_little_more_effort() {}
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected 3 parameters, found 0
+   |
+help: modify the signature to match the trait definition
+   |
+LL |     fn come_on_a_little_more_effort(_: (), _: (), _: ()) {}
+   |                                     +++++++++++++++++++
 
 error: aborting due to 1 previous error
 

tests/ui/impl-trait/in-trait/method-signature-matches.too_many.stderr

@@ -6,6 +6,12 @@ LL |     fn calm_down_please() -> impl Sized;
 ...
 LL |     fn calm_down_please(_: (), _: (), _: ()) {}
    |                            ^^^^^^^^^^^^^^^^ expected 0 parameters, found 3
+   |
+help: modify the signature to match the trait definition
+   |
+LL -     fn calm_down_please(_: (), _: (), _: ()) {}
+LL +     fn calm_down_please() {}
+   |
 
 error: aborting due to 1 previous error
 

tests/ui/traits/impl-different-num-params.stderr

@@ -6,6 +6,11 @@ LL |     fn bar(&self, x: usize) -> Self;
 ...
 LL |     fn bar(&self) -> isize {
    |            ^^^^^ expected 2 parameters, found 1
+   |
+help: modify the signature to match the trait definition
+   |
+LL |     fn bar(&self, x: usize) -> isize {
+   |                 ++++++++++
 
 error: aborting due to 1 previous error