Do not use casting for suggestion to add type to numeric literal

Author: estebank

src/librustc/hir/mod.rs

@@ -241,7 +241,7 @@ pub struct LifetimeDef {
 }
 
 /// A "Path" is essentially Rust's notion of a name; for instance:
-/// std::cmp::PartialEq  .  It's represented as a sequence of identifiers,
+/// `std::cmp::PartialEq`. It's represented as a sequence of identifiers,
 /// along with a bunch of supporting information.
 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash)]
 pub struct Path {

src/librustc_typeck/check/method/suggest.rs

@@ -215,20 +215,43 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                             item_name,
                             ty_string
                         );
-                        let snippet = tcx.sess.codemap().span_to_snippet(expr.span)
-                            .unwrap_or("4".to_string());
                         let concrete_type = if actual.is_integral() {
-                            "u32"
+                            "i32"
                         } else {
                             "f32"
                         };
-                        err.span_suggestion(expr.span,
-                                            &format!("you must specify a concrete type for \
-                                                      this numeric value, like `{}`",
-                                                     concrete_type),
-                                            format!("({} as {})",
-                                                    snippet,
-                                                    concrete_type));
+                        match expr.node {
+                            hir::ExprLit(_) => {  // numeric literal
+                                let snippet = tcx.sess.codemap().span_to_snippet(expr.span)
+                                    .unwrap_or("<numeric literal>".to_string());
+                                // FIXME: use the literal for missing snippet
+
+                                err.span_suggestion(expr.span,
+                                                    &format!("you must specify a concrete type for \
+                                                              this numeric value, like `{}`",
+                                                             concrete_type),
+                                                    format!("{}_{}",
+                                                            snippet,
+                                                            concrete_type));
+                            }
+                            hir::ExprPath(ref qpath) => {  // local binding
+                                if let &hir::QPath::Resolved(_, ref path) = &qpath {
+                                    if let hir::def::Def::Local(node_id) = path.def {
+                                        let span = tcx.hir.span(node_id);
+                                        let snippet = tcx.sess.codemap().span_to_snippet(span)
+                                            .unwrap();
+                                        err.span_suggestion(span,
+                                                            &format!("you must specify a type for \
+                                                                      this binding, like `{}`",
+                                                                     concrete_type),
+                                                            format!("{}: {}",
+                                                                    snippet,
+                                                                    concrete_type));
+                                    }
+                                }
+                            }
+                            _ => {}
+                        }
                         err.emit();
                         return;
                     } else {

src/librustc_typeck/diagnostics.rs

@@ -4661,9 +4661,10 @@ x.powi(2);  // same error as above
 Because of this, you must give the numeric literal or binding a type:
 
 ```
-let _ = (2.0 as f32).powi(2);
+let _ = 2.0_f32.powi(2);
 let x: f32 = 2.0;
 let _ = x.powi(2);
+let _ = (2.0 as f32).powi(2);
 ```
 "##,
 }

src/test/ui/issue-41652/issue_41652.stderr

@@ -3,10 +3,10 @@ error[E0689]: can't call method `f` on ambiguous numeric type `{integer}`
    |
 19 |         3.f()
    |           ^
-help: you must specify a concrete type for this numeric value, like `u32`
+help: you must specify a concrete type for this numeric value, like `i32`
    |
-19 |         (3 as u32).f()
-   |         ^^^^^^^^^^
+19 |         3_i32.f()
+   |         ^^^^^
 
 error: aborting due to previous error
 

src/test/ui/macros/macro-backtrace-invalid-internals.stderr

@@ -35,8 +35,8 @@ error[E0689]: can't call method `powi` on ambiguous numeric type `{float}`
    |     -------------------- in this macro invocation
 help: you must specify a concrete type for this numeric value, like `f32`
    |
-51 |           (2.0 as f32).powi(2) //~ ERROR can't call method `powi` on ambiguous numeric type `{float}`
-   |           ^^^^^^^^^^^^
+51 |           2.0_f32.powi(2) //~ ERROR can't call method `powi` on ambiguous numeric type `{float}`
+   |           ^^^^^^^
 
 error[E0599]: no method named `fake` found for type `{integer}` in the current scope
   --> $DIR/macro-backtrace-invalid-internals.rs:33:13
@@ -75,8 +75,8 @@ error[E0689]: can't call method `powi` on ambiguous numeric type `{float}`
    |             ------------------- in this macro invocation
 help: you must specify a concrete type for this numeric value, like `f32`
    |
-57 |           (2.0 as f32).powi(2) //~ ERROR can't call method `powi` on ambiguous numeric type `{float}`
-   |           ^^^^^^^^^^^^
+57 |           2.0_f32.powi(2) //~ ERROR can't call method `powi` on ambiguous numeric type `{float}`
+   |           ^^^^^^^
 
 error: aborting due to 8 previous errors
 

src/test/ui/suggestions/method-on-ambiguous-numeric-type.rs

@@ -11,5 +11,8 @@
 fn main() {
     let x = 2.0.powi(2);
     //~^ ERROR can't call method `powi` on ambiguous numeric type `{float}`
+    let y = 2.0;
+    let x = y.powi(2);
+    //~^ ERROR can't call method `powi` on ambiguous numeric type `{float}`
     println!("{:?}", x);
 }

src/test/ui/suggestions/method-on-ambiguous-numeric-type.stderr

@@ -5,8 +5,18 @@ error[E0689]: can't call method `powi` on ambiguous numeric type `{float}`
    |                 ^^^^
 help: you must specify a concrete type for this numeric value, like `f32`
    |
-12 |     let x = (2.0 as f32).powi(2);
-   |             ^^^^^^^^^^^^
+12 |     let x = 2.0_f32.powi(2);
+   |             ^^^^^^^
 
-error: aborting due to previous error
+error[E0689]: can't call method `powi` on ambiguous numeric type `{float}`
+  --> $DIR/method-on-ambiguous-numeric-type.rs:15:15
+   |
+15 |     let x = y.powi(2);
+   |               ^^^^
+help: you must specify a type for this binding, like `f32`
+   |
+14 |     let y: f32 = 2.0;
+   |         ^^^^^^
+
+error: aborting due to 2 previous errors