From 8542dd02a8c00bba435efe0bed20bc9bb22e7ec5 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Esteban=20K=C3=BCber?= <esteban@kuber.com.ar>
Date: Tue, 7 Jun 2022 13:39:21 -0700
Subject: [PATCH] Use more targeted suggestion when confusing i8 with std::i8

---
 compiler/rustc_typeck/src/astconv/mod.rs      | 19 +++++++--------
 .../rustc_typeck/src/check/method/suggest.rs  | 24 ++++++++-----------
 .../suggest-std-when-using-type.stderr        |  4 ++--
 3 files changed, 21 insertions(+), 26 deletions(-)

diff --git a/compiler/rustc_typeck/src/astconv/mod.rs b/compiler/rustc_typeck/src/astconv/mod.rs
index bcff2ae512909..b1e180c701f50 100644
--- a/compiler/rustc_typeck/src/astconv/mod.rs
+++ b/compiler/rustc_typeck/src/astconv/mod.rs
@@ -1575,18 +1575,17 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         name: Symbol,
     ) -> ErrorGuaranteed {
         let mut err = struct_span_err!(self.tcx().sess, span, E0223, "ambiguous associated type");
-        if let (true, Ok(snippet)) = (
-            self.tcx()
-                .resolutions(())
-                .confused_type_with_std_module
-                .keys()
-                .any(|full_span| full_span.contains(span)),
-            self.tcx().sess.source_map().span_to_snippet(span),
-        ) {
+        if self
+            .tcx()
+            .resolutions(())
+            .confused_type_with_std_module
+            .keys()
+            .any(|full_span| full_span.contains(span))
+        {
             err.span_suggestion(
-                span,
+                span.shrink_to_lo(),
                 "you are looking for the module in `std`, not the primitive type",
-                format!("std::{}", snippet),
+                "std::".to_string(),
                 Applicability::MachineApplicable,
             );
         } else {
diff --git a/compiler/rustc_typeck/src/check/method/suggest.rs b/compiler/rustc_typeck/src/check/method/suggest.rs
index 0e198907c8d50..4071c389266d3 100644
--- a/compiler/rustc_typeck/src/check/method/suggest.rs
+++ b/compiler/rustc_typeck/src/check/method/suggest.rs
@@ -327,26 +327,22 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     );
                 }
                 if let Some(span) = tcx.resolutions(()).confused_type_with_std_module.get(&span) {
-                    if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(*span) {
-                        err.span_suggestion(
-                            *span,
-                            "you are looking for the module in `std`, \
-                                     not the primitive type",
-                            format!("std::{}", snippet),
-                            Applicability::MachineApplicable,
-                        );
-                    }
+                    err.span_suggestion(
+                        span.shrink_to_lo(),
+                        "you are looking for the module in `std`, not the primitive type",
+                        "std::".to_string(),
+                        Applicability::MachineApplicable,
+                    );
                 }
                 if let ty::RawPtr(_) = &actual.kind() {
                     err.note(
                         "try using `<*const T>::as_ref()` to get a reference to the \
-                                      type behind the pointer: https://doc.rust-lang.org/std/\
-                                      primitive.pointer.html#method.as_ref",
+                         type behind the pointer: https://doc.rust-lang.org/std/\
+                         primitive.pointer.html#method.as_ref",
                     );
                     err.note(
-                        "using `<*const T>::as_ref()` on a pointer \
-                                      which is unaligned or points to invalid \
-                                      or uninitialized memory is undefined behavior",
+                        "using `<*const T>::as_ref()` on a pointer which is unaligned or points \
+                         to invalid or uninitialized memory is undefined behavior",
                     );
                 }
 
diff --git a/src/test/ui/suggestions/suggest-std-when-using-type.stderr b/src/test/ui/suggestions/suggest-std-when-using-type.stderr
index 4255281d9a7ac..2840fa121a75f 100644
--- a/src/test/ui/suggestions/suggest-std-when-using-type.stderr
+++ b/src/test/ui/suggestions/suggest-std-when-using-type.stderr
@@ -7,7 +7,7 @@ LL |     let pi = f32::consts::PI;
 help: you are looking for the module in `std`, not the primitive type
    |
 LL |     let pi = std::f32::consts::PI;
-   |              ~~~~~~~~~~~~~~~~
+   |              +++++
 
 error[E0599]: no function or associated item named `from_utf8` found for type `str` in the current scope
   --> $DIR/suggest-std-when-using-type.rs:5:14
@@ -18,7 +18,7 @@ LL |         str::from_utf8(bytes)
 help: you are looking for the module in `std`, not the primitive type
    |
 LL |         std::str::from_utf8(bytes)
-   |         ~~~~~~~~~~~~~~~~~~~
+   |         +++++
 
 error: aborting due to 2 previous errors