Suggest borrowing arguments in generic positions when trait bounds are satisfied

This subsumes the suggestions to borrow arguments with `AsRef`/`Borrow` bounds and those to borrow
arguments with `Fn` and `FnMut` bounds. It works for other traits implemented on references as well,
such as `std::io::Read`, `std::io::Write`, and `core::fmt::Write`.
Incidentally, by making the logic for suggesting borrowing closures general, this removes some
spurious suggestions to mutably borrow `FnMut` closures in assignments, as well as an unhelpful
suggestion to add a `Clone` constraint to an `impl Fn` argument.

Author: dianne

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -11,10 +11,6 @@ note: closure cannot be moved more than once as it is not `Copy` due to moving t
  |
 LL | if let MultiVariant::Point(ref mut x, _) = point {
  | ^^^^^
-help: consider mutably borrowing `c`
- |
-LL | let a = &mut c;
- | ++++
 
 error: aborting due to 1 previous error
 

tests/ui/closures/2229_closure_analysis/diagnostics/closure-origin-multi-variant-diagnostics.stderr

@@ -11,10 +11,6 @@ note: closure cannot be moved more than once as it is not `Copy` due to moving t
  |
 LL | let SingleVariant::Point(ref mut x, _) = point;
  | ^^^^^
-help: consider mutably borrowing `c`
- |
-LL | let b = &mut c;
- | ++++
 
 error: aborting due to 1 previous error
 

tests/ui/closures/2229_closure_analysis/diagnostics/closure-origin-single-variant-diagnostics.stderr

@@ -11,10 +11,6 @@ note: closure cannot be moved more than once as it is not `Copy` due to moving t
  |
 LL | x.y.a += 1;
  | ^^^^^
-help: consider mutably borrowing `hello`
- |
-LL | let b = &mut hello;
- | ++++
 
 error: aborting due to 1 previous error
 

tests/ui/closures/2229_closure_analysis/diagnostics/closure-origin-struct-diagnostics.stderr

@@ -11,10 +11,6 @@ note: closure cannot be moved more than once as it is not `Copy` due to moving t
  |
 LL | x.0 += 1;
  | ^^^
-help: consider mutably borrowing `hello`
- |
-LL | let b = &mut hello;
- | ++++
 
 error: aborting due to 1 previous error
 

tests/ui/closures/2229_closure_analysis/diagnostics/closure-origin-tuple-diagnostics-1.stderr

@@ -1,23 +1,20 @@
 //! auxiliary definitons for suggest-borrow-for-generic-arg.rs, to ensure the suggestion works on
 //! functions defined in other crates.
 
-use std::borrow::{Borrow,BorrowMut};
-use std::convert::{AsMut,AsRef};
-pubstructBar;
+use std::io::{self,Read,Write};
+use std::iter::Sum;
 
-implAsRef<Bar>forBar{
-fnas_ref(&self) -> &Bar{
-self
-}
+pubfnwrite_stuff<W:Write>(mutwriter:W) -> io::Result<()>{
+writeln!(writer,"stuff")
 }
 
-implAsMut<Bar>forBar{
-fnas_mut(&mutself) -> &mutBar{
-self
-}
+pubfnread_and_discard<R:Read>(mutreader:R) -> io::Result<()>{
+letmut buf = Vec::new();
+ reader.read_to_end(&mut buf).map(|_| ())
 }
 
-pubfnfoo<T:AsRef<Bar>>(_:T){}
-pubfnqux<T:AsMut<Bar>>(_:T){}
-pubfnbat<T:Borrow<T>>(_:T){}
-pubfnbaz<T:BorrowMut<T>>(_:T){}
+pubfnsum_three<I:IntoIterator>(iter:I) -> <IasIntoIterator>::Item
+where <IasIntoIterator>::Item:Sum
+{
+ iter.into_iter().take(3).sum()
+}

tests/ui/moves/auxiliary/suggest-borrow-for-generic-arg-aux.rs

@@ -1,4 +1,4 @@
-fntakes_fn(f:implFn()){//~ HELP if `impl Fn()` implemented `Clone`
+fntakes_fn(f:implFn()){
 loop{
 takes_fnonce(f);
 //~^ ERROR use of moved value

tests/ui/moves/borrow-closures-instead-of-move.rs

@@ -8,21 +8,6 @@ LL | loop {
 LL | takes_fnonce(f);
  | ^ value moved here, in previous iteration of loop
  |
-note: consider changing this parameter type in function `takes_fnonce` to borrow instead if owning the value isn't necessary
- --> $DIR/borrow-closures-instead-of-move.rs:34:20
- |
-LL | fn takes_fnonce(_: impl FnOnce()) {}
- | ------------ ^^^^^^^^^^^^^ this parameter takes ownership of the value
- | |
- | in this function
-help: if `impl Fn()` implemented `Clone`, you could clone the value
- --> $DIR/borrow-closures-instead-of-move.rs:1:16
- |
-LL | fn takes_fn(f: impl Fn()) {
- | ^^^^^^^^^ consider constraining this type parameter with `Clone`
-LL | loop {
-LL | takes_fnonce(f);
- | - you could clone this value
 help: consider borrowing `f`
  |
 LL | takes_fnonce(&f);
@@ -40,13 +25,6 @@ LL | takes_fnonce(m);
 LL | takes_fnonce(m);
  | ^ value used here after move
  |
-note: consider changing this parameter type in function `takes_fnonce` to borrow instead if owning the value isn't necessary
- --> $DIR/borrow-closures-instead-of-move.rs:34:20
- |
-LL | fn takes_fnonce(_: impl FnOnce()) {}
- | ------------ ^^^^^^^^^^^^^ this parameter takes ownership of the value
- | |
- | in this function
 help: if `impl FnMut()` implemented `Clone`, you could clone the value
  --> $DIR/borrow-closures-instead-of-move.rs:9:20
  |

tests/ui/moves/borrow-closures-instead-of-move.stderr

@@ -24,10 +24,6 @@ LL | fn conspirator<F>(mut f: F) where F: FnMut(&mut R, bool) {
  | ^ consider constraining this type parameter with `Clone`
 LL | let mut r = R {c: Box::new(f)};
  | - you could clone this value
-help: consider mutably borrowing `f`
- |
-LL | let mut r = R {c: Box::new(&mut f)};
- | ++++
 
 error: aborting due to 2 previous errors
 

tests/ui/moves/moves-based-on-type-no-recursive-stack-closure.stderr

@@ -1,22 +1,46 @@
-//! Test suggetions to borrow generic arguments instead of moving when all predicates hold after
-//! substituting in the reference type.
+//! Test suggetions to borrow generic arguments instead of moving. Tests for other instances of this
+//! can be found in `moved-value-on-as-ref-arg.rs` and `borrow-closures-instead-of-move.rs`
 //@ run-rustfix
-//@ aux-build:suggest-borrow-for-generic-arg-aux.rs
+//@ aux-crate:aux=suggest-borrow-for-generic-arg-aux.rs
+//@ edition: 2021
 
 #![allow(unused_mut)]
-extern crate suggest_borrow_for_generic_arg_aux as aux;
+use std::io::{self, Write};
 
-pub fn main() {
- let bar = aux::Bar;
- aux::foo(&bar); //~ HELP consider borrowing `bar`
- let _baa = bar; //~ ERROR use of moved value
- let mut bar = aux::Bar;
- aux::qux(&mut bar); //~ HELP consider mutably borrowing `bar`
- let _baa = bar; //~ ERROR use of moved value
- let bar = aux::Bar;
- aux::bat(&bar); //~ HELP consider borrowing `bar`
- let _baa = bar; //~ ERROR use of moved value
- let mut bar = aux::Bar;
- aux::baz(&mut bar); //~ HELP consider mutably borrowing `bar`
- let _baa = bar; //~ ERROR use of moved value
+// test for `std::io::Write` (#131413)
+fn test_write() -> io::Result<()> {
+ let mut stdout = io::stdout();
+ aux::write_stuff(&stdout)?; //~ HELP consider borrowing `stdout`
+ writeln!(stdout, "second line")?; //~ ERROR borrow of moved value: `stdout`
+
+ let mut buf = Vec::new();
+ aux::write_stuff(&mut buf.clone())?; //~ HELP consider mutably borrowing `buf`
+ //~^ HELP consider cloning the value
+ writeln!(buf, "second_line") //~ ERROR borrow of moved value: `buf`
+}
+
+/// test for `std::io::Read` (#131413)
+fn test_read() -> io::Result<()> {
+ let stdin = io::stdin();
+ aux::read_and_discard(&stdin)?; //~ HELP consider borrowing `stdin`
+ aux::read_and_discard(stdin)?; //~ ERROR use of moved value: `stdin`
+
+ let mut bytes = std::collections::VecDeque::from([1, 2, 3, 4, 5, 6]);
+ aux::read_and_discard(&mut bytes.clone())?; //~ HELP consider mutably borrowing `bytes`
+ //~^ HELP consider cloning the value
+ aux::read_and_discard(bytes) //~ ERROR use of moved value: `bytes`
+}
+
+/// test that suggestions work with projection types in the callee's signature
+fn test_projections() {
+ let mut iter = [1, 2, 3, 4, 5, 6].into_iter();
+ let _six: usize = aux::sum_three(&mut iter.clone()); //~ HELP consider mutably borrowing `iter`
+ //~^ HELP consider cloning the value
+ let _fifteen: usize = aux::sum_three(iter); //~ ERROR use of moved value: `iter`
+}
+
+fn main() {
+ test_write().unwrap();
+ test_read().unwrap();
+ test_projections();
 }