Auto merge of #47171 - estebank:numeric-literal-suggestion, r=nikomatsakis

Provide suggestion when trying to use method on numeric literal

New output:

```
error[E0688]: can't call method `powi` on ambiguous numeric type `{float}`
  --> $DIR/method-on-ambiguous-numeric-type.rs:12:17
   |
12 |     let x = 2.0.powi(2);
   |                 ^^^^
help: you must specify a concrete type for this numeric value, like `f32`
   |
12 |     let x = 2.0_f32.powi(2);
   |             ^^^^^^^
```

Previous output:

```
error[E0599]: no method named `powi` found for type `{float}` in the current scope
  --> src/main.rs:12:17
   |
12 |     let x = 2.0.powi(2);
   |                 ^^^^
   |
   = help: items from traits can only be used if the trait is in scope
help: the following trait is implemented but not in scope, perhaps add a `use` for it:
   |
11 | use core::num::Float;
   |
```

Fix #40985.

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

@@ -195,6 +195,66 @@ pub fn report_method_error(&self,
                     }
                 };
                 let mut err = if !actual.references_error() {
+                    // Suggest clamping down the type if the method that is being attempted to
+                    // be used exists at all, and the type is an ambiuous numeric type
+                    // ({integer}/{float}).
+                    let mut candidates = all_traits(self.tcx)
+                        .filter(|info| {
+                            self.associated_item(info.def_id, item_name, Namespace::Value).is_some()
+                        });
+                    if let (true, false, Some(expr), Some(_)) = (actual.is_numeric(),
+                                                                 actual.has_concrete_skeleton(),
+                                                                 rcvr_expr,
+                                                                 candidates.next()) {
+                        let mut err = struct_span_err!(
+                            tcx.sess,
+                            span,
+                            E0689,
+                            "can't call {} `{}` on ambiguous numeric type `{}`",
+                            type_str,
+                            item_name,
+                            ty_string
+                        );
+                        let concrete_type = if actual.is_integral() {
+                            "i32"
+                        } else {
+                            "f32"
+                        };
+                        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 {
                         struct_span_err!(
                             tcx.sess,
                             span,
@@ -204,6 +264,7 @@ pub fn report_method_error(&self,
                             item_name,
                             ty_string
                         )
+                    }
                 } else {
                     tcx.sess.diagnostic().struct_dummy()
                 };
@@ -305,12 +366,16 @@ pub fn report_method_error(&self,
                                       bound_list));
                 }
 
+                if actual.is_numeric() && actual.is_fresh() {
+
+                } else {
                     self.suggest_traits_to_import(&mut err,
                                                   span,
                                                   rcvr_ty,
                                                   item_name,
                                                   rcvr_expr,
                                                   out_of_scope_traits);
+                }
 
                 if let Some(lev_candidate) = lev_candidate {
                     err.help(&format!("did you mean `{}`?", lev_candidate.name));

src/librustc_typeck/diagnostics.rs

@@ -4641,6 +4641,32 @@ fn foo<U: Iterator>(&self, _: &U) { } // error method `foo` has incompatible
 ```
 "##,
 
+E0689: r##"
+This error indicates that the numeric value for the method being passed exists
+but the type of the numeric value or binding could not be identified.
+
+The error happens on numeric literals:
+
+```compile_fail,E0689
+2.0.powi(2);
+```
+
+and on numeric bindings without an identified concrete type:
+
+```compile_fail,E0689
+let x = 2.0;
+x.powi(2);  // same error as above
+```
+
+Because of this, you must give the numeric literal or binding a type:
+
+```
+let _ = 2.0_f32.powi(2);
+let x: f32 = 2.0;
+let _ = x.powi(2);
+let _ = (2.0 as f32).powi(2);
+```
+"##,
 }
 
 register_diagnostics! {

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

@@ -17,7 +17,7 @@
 impl issue_41652_b::Tr for S {
     fn f() {
         3.f()
-        //~^ ERROR no method named `f` found for type `{integer}` in the current scope
+        //~^ ERROR can't call method `f` on ambiguous numeric type `{integer}`
     }
 }
 

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

-error[E0599]: no method named `f` found for type `{integer}` in the current scope
+error[E0689]: can't call method `f` on ambiguous numeric type `{integer}`
   --> $DIR/issue_41652.rs:19:11
    |
 19 |         3.f()
    |           ^
+help: you must specify a concrete type for this numeric value, like `i32`
    |
-   = note: found the following associated functions; to be used as methods, functions must have a `self` parameter
-   = help: try with `{integer}::f`
-note: candidate #1 is defined in the trait `issue_41652_b::Tr`
-  --> $DIR/auxiliary/issue_41652_b.rs:14:5
-   |
-14 | /     fn f()
-15 | |         where Self: Sized;
-   | |__________________________^
-   = help: to disambiguate the method call, write `issue_41652_b::Tr::f(3)` instead
+19 |         3_i32.f()
+   |         ^^^^^
 
 error: aborting due to previous error
 

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

@@ -46,12 +46,26 @@
      }
 }
 
+macro_rules! real_method_stmt {
+     () => {
+          2.0.powi(2) //~ ERROR can't call method `powi` on ambiguous numeric type `{float}`
+     }
+}
+
+macro_rules! real_method_expr {
+     () => {
+          2.0.powi(2) //~ ERROR can't call method `powi` on ambiguous numeric type `{float}`
+     }
+}
+
 fn main() {
     fake_method_stmt!();
     fake_field_stmt!();
     fake_anon_field_stmt!();
+    real_method_stmt!();
 
     let _ = fake_method_expr!();
     let _ = fake_field_expr!();
     let _ = fake_anon_field_expr!();
+    let _ = real_method_expr!();
 }

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

@@ -4,7 +4,7 @@ error[E0599]: no method named `fake` found for type `{integer}` in the current s
 15 |           1.fake() //~ ERROR no method
    |             ^^^^
 ...
-50 |     fake_method_stmt!();
+62 |     fake_method_stmt!();
    |     -------------------- in this macro invocation
 
 error[E0610]: `{integer}` is a primitive type and therefore doesn't have fields
@@ -13,7 +13,7 @@ error[E0610]: `{integer}` is a primitive type and therefore doesn't have fields
 21 |           1.fake //~ ERROR doesn't have fields
    |             ^^^^
 ...
-51 |     fake_field_stmt!();
+63 |     fake_field_stmt!();
    |     ------------------- in this macro invocation
 
 error[E0609]: no field `0` on type `{integer}`
@@ -22,16 +22,29 @@ error[E0609]: no field `0` on type `{integer}`
 27 |           (1).0 //~ ERROR no field
    |           ^^^^^
 ...
-52 |     fake_anon_field_stmt!();
+64 |     fake_anon_field_stmt!();
    |     ------------------------ in this macro invocation
 
+error[E0689]: can't call method `powi` on ambiguous numeric type `{float}`
+  --> $DIR/macro-backtrace-invalid-internals.rs:51:15
+   |
+51 |           2.0.powi(2) //~ ERROR can't call method `powi` on ambiguous numeric type `{float}`
+   |               ^^^^
+...
+65 |     real_method_stmt!();
+   |     -------------------- in this macro invocation
+help: you must specify a concrete type for this numeric value, like `f32`
+   |
+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
    |
 33 |           1.fake() //~ ERROR no method
    |             ^^^^
 ...
-54 |     let _ = fake_method_expr!();
+67 |     let _ = fake_method_expr!();
    |             ------------------- in this macro invocation
 
 error[E0610]: `{integer}` is a primitive type and therefore doesn't have fields
@@ -40,7 +53,7 @@ error[E0610]: `{integer}` is a primitive type and therefore doesn't have fields
 39 |           1.fake //~ ERROR doesn't have fields
    |             ^^^^
 ...
-55 |     let _ = fake_field_expr!();
+68 |     let _ = fake_field_expr!();
    |             ------------------ in this macro invocation
 
 error[E0609]: no field `0` on type `{integer}`
@@ -49,8 +62,21 @@ error[E0609]: no field `0` on type `{integer}`
 45 |           (1).0 //~ ERROR no field
    |           ^^^^^
 ...
-56 |     let _ = fake_anon_field_expr!();
+69 |     let _ = fake_anon_field_expr!();
    |             ----------------------- in this macro invocation
 
-error: aborting due to 6 previous errors
+error[E0689]: can't call method `powi` on ambiguous numeric type `{float}`
+  --> $DIR/macro-backtrace-invalid-internals.rs:57:15
+   |
+57 |           2.0.powi(2) //~ ERROR can't call method `powi` on ambiguous numeric type `{float}`
+   |               ^^^^
+...
+70 |     let _ = real_method_expr!();
+   |             ------------------- in this macro invocation
+help: you must specify a concrete type for this numeric value, like `f32`
+   |
+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

+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+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

+error[E0689]: can't call method `powi` on ambiguous numeric type `{float}`
+  --> $DIR/method-on-ambiguous-numeric-type.rs:12:17
+   |
+12 |     let x = 2.0.powi(2);
+   |                 ^^^^
+help: you must specify a concrete type for this numeric value, like `f32`
+   |
+12 |     let x = 2.0_f32.powi(2);
+   |             ^^^^^^^
+
+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
+