Improve the error message when resolution of methods/items finds no matching impl.

Author: quantheory

src/librustc_typeck/check/method/mod.rs

@@ -40,7 +40,7 @@ pub enum MethodError {
     // Did not find an applicable method, but we did find various
     // static methods that may apply, as well as a list of
     // not-in-scope traits which may work.
-    NoMatch(Vec<CandidateSource>, Vec<ast::DefId>),
+    NoMatch(Vec<CandidateSource>, Vec<ast::DefId>, probe::Mode),
 
     // Multiple methods might apply.
     Ambiguity(Vec<CandidateSource>),

src/librustc_typeck/check/method/probe.rs

@@ -136,7 +136,7 @@ pub fn probe<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
     let steps = if mode == Mode::MethodCall {
         match create_steps(fcx, span, self_ty) {
             Some(steps) => steps,
-            None => return Err(MethodError::NoMatch(Vec::new(), Vec::new())),
+            None => return Err(MethodError::NoMatch(Vec::new(), Vec::new(), mode)),
         }
     } else {
         vec![CandidateStep {
@@ -866,7 +866,7 @@ impl<'a,'tcx> ProbeContext<'a,'tcx> {
                     }
                 }
             }).collect(),
-            Some(Err(MethodError::NoMatch(_, others))) => {
+            Some(Err(MethodError::NoMatch(_, others, _))) => {
                 assert!(others.is_empty());
                 vec![]
             }
@@ -877,7 +877,7 @@ impl<'a,'tcx> ProbeContext<'a,'tcx> {
             None => vec![],
         };
 
-        Err(MethodError::NoMatch(static_candidates, out_of_scope_traits))
+        Err(MethodError::NoMatch(static_candidates, out_of_scope_traits, self.mode))
     }
 
     fn pick_core(&mut self) -> Option<PickResult<'tcx>> {

src/librustc_typeck/check/method/suggest.rs

@@ -28,6 +28,7 @@ use std::cell;
 use std::cmp::Ordering;
 
 use super::{MethodError, CandidateSource, impl_item, trait_item};
+use super::probe::Mode;
 
 pub fn report_error<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
                               span: Span,
@@ -42,17 +43,19 @@ pub fn report_error<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
     }
 
     match error {
-        MethodError::NoMatch(static_sources, out_of_scope_traits) => {
+        MethodError::NoMatch(static_sources, out_of_scope_traits, mode) => {
             let cx = fcx.tcx();
             let item_ustring = item_name.user_string(cx);
 
             fcx.type_error_message(
                 span,
                 |actual| {
-                    format!("type `{}` does not implement any \
-                             item in scope named `{}`",
-                            actual,
-                            item_ustring)
+                    format!("no {} named `{}` found for type `{}` \
+                             in the current scope",
+                            if mode == Mode::MethodCall { "method" }
+                            else { "associated item" },
+                            item_ustring,
+                            actual)
                 },
                 rcvr_ty,
                 None);

src/test/compile-fail/auto-ref-slice-plus-ref.rs

@@ -15,11 +15,11 @@ fn main() {
     // vectors to slices then automatically create a self reference.
 
     let mut a = vec!(0);
-    a.test_mut(); //~ ERROR does not implement any item in scope named `test_mut`
-    a.test(); //~ ERROR does not implement any item in scope named `test`
+    a.test_mut(); //~ ERROR no method named `test_mut` found
+    a.test(); //~ ERROR no method named `test` found
 
-    ([1]).test(); //~ ERROR does not implement any item in scope named `test`
-    (&[1]).test(); //~ ERROR does not implement any item in scope named `test`
+    ([1]).test(); //~ ERROR no method named `test` found
+    (&[1]).test(); //~ ERROR no method named `test` found
 }
 
 trait MyIter {

src/test/compile-fail/class-cast-to-trait.rs

@@ -60,5 +60,5 @@ fn cat(in_x : usize, in_y : isize, in_name: String) -> cat {
 
 fn main() {
   let nyan: Box<noisy> = box cat(0, 2, "nyan".to_string()) as Box<noisy>;
-  nyan.eat(); //~ ERROR does not implement any item in scope named `eat`
+  nyan.eat(); //~ ERROR no method named `eat` found
 }

src/test/compile-fail/coherence_inherent.rs

@@ -38,7 +38,7 @@ mod NoImport {
     use Lib::TheStruct;
 
     fn call_the_fn(s: &TheStruct) {
-        s.the_fn(); //~ ERROR does not implement any item in scope named `the_fn`
+        s.the_fn(); //~ ERROR no method named `the_fn` found
     }
 }
 

src/test/compile-fail/coherence_inherent_cc.rs

@@ -30,7 +30,7 @@ mod NoImport {
     use coherence_inherent_cc_lib::TheStruct;
 
     fn call_the_fn(s: &TheStruct) {
-        s.the_fn(); //~ ERROR does not implement any item in scope named `the_fn`
+        s.the_fn(); //~ ERROR no method named `the_fn` found
     }
 }
 

src/test/compile-fail/copy-a-resource.rs

@@ -26,6 +26,6 @@ fn foo(i:isize) -> foo {
 fn main() {
     let x = foo(10);
     let _y = x.clone();
-    //~^ ERROR does not implement any item in scope
+    //~^ ERROR no method named `clone` found
     println!("{:?}", x);
 }

src/test/compile-fail/issue-10465.rs

@@ -24,7 +24,7 @@ pub mod b {
         use b::B;
 
         fn foo(b: &B) {
-            b.foo(); //~ ERROR: does not implement any item in scope named
+            b.foo(); //~ ERROR: no method named `foo` found
         }
     }
 

src/test/compile-fail/issue-13853.rs

@@ -31,7 +31,7 @@ impl Node for Stuff {
 }
 
 fn iterate<N: Node, G: Graph<N>>(graph: &G) {
-    for node in graph.iter() { //~ ERROR does not implement any item in scope named
+    for node in graph.iter() { //~ ERROR no method named `iter` found
         node.zomg();  //~ error: the type of this value must be known in this context
     }
 }