Get span_to_snippet and rewrite it more idiomatically

Author: Kivooeo

compiler/rustc_hir_typeck/src/expr.rs

@@ -3278,24 +3278,21 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     }
 
     fn suggest_first_deref_field(&self, err: &mut Diag<'_>, base: &hir::Expr<'_>, field: Ident) {
-        let full_span = base.span.to(field.span);
-
-        let base_snippet = self
-            .tcx
-            .sess
-            .source_map()
-            .span_to_snippet(base.span)
-            .unwrap_or_else(|_| "ptr".to_string());
-
-        let replacement = format!("(*{}).{}", base_snippet, field.name);
-
-        err.span_label(full_span, "unknown field access via raw pointer");
-
-        err.span_suggestion_verbose(
-            full_span,
-            "use `.` on a dereferenced raw pointer instead",
-            replacement,
-            Applicability::MachineApplicable,
+        err.span_label(field.span, "unknown field");
+        let val = if let Ok(base) = self.tcx.sess.source_map().span_to_snippet(base.span)
+            && base.len() < 20
+        {
+            format!("{base}")
+        } else {
+            "the value".to_string()
+        };
+        err.multipart_suggestion(
+            format!("`{val}` is a raw pointer; try dereferencing it"),
+            vec![
+                (base.span.shrink_to_lo(), "(*".into()),
+                (base.span.to(field.span.shrink_to_lo()), format!("{val}).")),
+            ],
+            Applicability::MaybeIncorrect,
         );
     }
 

tests/ui/issues/issue-11004.stderr

@@ -2,29 +2,23 @@ error[E0609]: no field `x` on type `*mut A`
   --> $DIR/issue-11004.rs:7:21
    |
 LL |     let x : i32 = n.x;
-   |                   --^
-   |                   |
-   |                   unknown field access via raw pointer
+   |                     ^ unknown field
    |
-help: use `.` on a dereferenced raw pointer instead
-   |
-LL -     let x : i32 = n.x;
-LL +     let x : i32 = (*n).x;
+help: `n` is a raw pointer; try dereferencing it
    |
+LL |     let x : i32 = (*n).x;
+   |                   ++ +
 
 error[E0609]: no field `y` on type `*mut A`
   --> $DIR/issue-11004.rs:8:21
    |
 LL |     let y : f64 = n.y;
-   |                   --^
-   |                   |
-   |                   unknown field access via raw pointer
-   |
-help: use `.` on a dereferenced raw pointer instead
+   |                     ^ unknown field
    |
-LL -     let y : f64 = n.y;
-LL +     let y : f64 = (*n).y;
+help: `n` is a raw pointer; try dereferencing it
    |
+LL |     let y : f64 = (*n).y;
+   |                   ++ +
 
 error: aborting due to 2 previous errors
 

tests/ui/suggestions/parenthesized-deref-suggestion.stderr

@@ -2,14 +2,12 @@ error[E0609]: no field `opts` on type `*const Session`
   --> $DIR/parenthesized-deref-suggestion.rs:7:30
    |
 LL |     (sess as *const Session).opts;
-   |     -------------------------^^^^
-   |     |
-   |     unknown field access via raw pointer
+   |                              ^^^^ unknown field
    |
-help: use `.` on a dereferenced raw pointer instead
+help: `the value` is a raw pointer; try dereferencing it
    |
 LL -     (sess as *const Session).opts;
-LL +     (*(sess as *const Session)).opts;
+LL +     (*the value).opts;
    |
 
 error[E0609]: no field `0` on type `[u32; 1]`

tests/ui/unsafe/unsafe-fn-autoderef.stderr

@@ -2,15 +2,12 @@ error[E0609]: no field `f` on type `*const Rec`
   --> $DIR/unsafe-fn-autoderef.rs:19:14
    |
 LL |     return p.f;
-   |            --^
-   |            |
-   |            unknown field access via raw pointer
+   |              ^ unknown field
    |
-help: use `.` on a dereferenced raw pointer instead
-   |
-LL -     return p.f;
-LL +     return (*p).f;
+help: `p` is a raw pointer; try dereferencing it
    |
+LL |     return (*p).f;
+   |            ++ +
 
 error: aborting due to 1 previous error