[gcc/devel/rust/master] Improve error message for failure in Method resolution

[Thomas Schwinge <tschwinge@gcc.gnu.org>]

https://gcc.gnu.org/g:d31c1bdaa8f0c08ec5517a0819b590e5650795ee

commit d31c1bdaa8f0c08ec5517a0819b590e5650795ee
Author: Philip Herron <philip.herron@embecosm.com>
Date:   Fri Jan 21 20:49:55 2022 +0000

    Improve error message for failure in Method resolution
    
    Use the locus for the method name segment and print its name as part of the
    error message improves the quality of the error handling in method
    resolution.
    
    Fixes #861

Diff:
---
 gcc/rust/typecheck/rust-hir-type-check-expr.h | 15 ++++-----------
 gcc/testsuite/rust/compile/method1.rs         |  2 +-
 2 files changed, 5 insertions(+), 12 deletions(-)

diff --git a/gcc/rust/typecheck/rust-hir-type-check-expr.h b/gcc/rust/typecheck/rust-hir-type-check-expr.h
index 1ac49463062..0ac924fa26e 100644
--- a/gcc/rust/typecheck/rust-hir-type-check-expr.h
+++ b/gcc/rust/typecheck/rust-hir-type-check-expr.h
@@ -299,17 +299,10 @@ public:
       = MethodResolution::Select (candidates, receiver_tyty, adjustments);
     if (resolved_candidate == nullptr)
       {
-	if (candidates.size () > 1)
-	  {
-	    // not sure if this is the correct error here
-	    ReportMultipleCandidateError::Report (
-	      candidates, expr.get_method_name ().get_segment (),
-	      expr.get_method_name ().get_locus ());
-	  }
-	else
-	  {
-	    rust_error_at (expr.get_locus (), "failed to resolve method");
-	  }
+	rust_error_at (
+	  expr.get_method_name ().get_locus (),
+	  "failed to resolve method for %<%s%>",
+	  expr.get_method_name ().get_segment ().as_string ().c_str ());
 	return;
       }
 
diff --git a/gcc/testsuite/rust/compile/method1.rs b/gcc/testsuite/rust/compile/method1.rs
index cce4ecfb683..18652406085 100644
--- a/gcc/testsuite/rust/compile/method1.rs
+++ b/gcc/testsuite/rust/compile/method1.rs
@@ -8,6 +8,6 @@ pub fn main() {
     a = Foo(123);
 
     a.test();
-    // { dg-error "failed to resolve method" "" { target *-*-* } .-1 }
+    // { dg-error "failed to resolve method for .test." "" { target *-*-* } .-1 }
     // { dg-error {failed to type resolve expression} "" { target *-*-* } .-2 }
 }