suggest iter_mut() where trying to modify elements from .iter()

9 files changed, 233 insertions, 0 deletions

diff --git a/tests/ui/borrowck/issue-115259-suggest-iter-mut.fixed b/tests/ui/borrowck/issue-115259-suggest-iter-mut.fixed
new file mode 100644
index 00000000000..4653fe7375d
--- /dev/null
+++ b/tests/ui/borrowck/issue-115259-suggest-iter-mut.fixed
@@ -0,0 +1,20 @@
+// run-rustfix
+#![allow(unused_mut)]
+#![allow(dead_code)]
+
+pub trait Layer {
+    fn process(&mut self) -> u32;
+}
+
+pub struct State {
+    layers: Vec<Box<dyn Layer>>,
+}
+
+impl State {
+    pub fn process(&mut self) -> u32 {
+        self.layers.iter_mut().fold(0, |result, mut layer| result + layer.process())
+        //~^ ERROR cannot borrow `**layer` as mutable, as it is behind a `&` reference
+    }
+}
+
+fn main() {}
diff --git a/tests/ui/borrowck/issue-115259-suggest-iter-mut.rs b/tests/ui/borrowck/issue-115259-suggest-iter-mut.rs
new file mode 100644
index 00000000000..e0f6ab1321f
--- /dev/null
+++ b/tests/ui/borrowck/issue-115259-suggest-iter-mut.rs
@@ -0,0 +1,20 @@
+// run-rustfix
+#![allow(unused_mut)]
+#![allow(dead_code)]
+
+pub trait Layer {
+    fn process(&mut self) -> u32;
+}
+
+pub struct State {
+    layers: Vec<Box<dyn Layer>>,
+}
+
+impl State {
+    pub fn process(&mut self) -> u32 {
+        self.layers.iter().fold(0, |result, mut layer| result + layer.process())
+        //~^ ERROR cannot borrow `**layer` as mutable, as it is behind a `&` reference
+    }
+}
+
+fn main() {}
diff --git a/tests/ui/borrowck/issue-115259-suggest-iter-mut.stderr b/tests/ui/borrowck/issue-115259-suggest-iter-mut.stderr
new file mode 100644
index 00000000000..7e0fc2cf298
--- /dev/null
+++ b/tests/ui/borrowck/issue-115259-suggest-iter-mut.stderr
@@ -0,0 +1,16 @@
+error[E0596]: cannot borrow `**layer` as mutable, as it is behind a `&` reference
+  --> $DIR/issue-115259-suggest-iter-mut.rs:15:65
+   |
+LL |         self.layers.iter().fold(0, |result, mut layer| result + layer.process())
+   |                                             ---------           ^^^^^ `layer` is a `&` reference, so the data it refers to cannot be borrowed as mutable
+   |                                             |
+   |                                             consider changing this binding's type to be: `&mut Box<dyn Layer>`
+   |
+help: you may want to use `iter_mut` here
+   |
+LL |         self.layers.iter_mut().fold(0, |result, mut layer| result + layer.process())
+   |                     ~~~~~~~~
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0596`.
diff --git a/tests/ui/borrowck/issue-62387-suggest-iter-mut-2.fixed b/tests/ui/borrowck/issue-62387-suggest-iter-mut-2.fixed
new file mode 100644
index 00000000000..f02374d8e11
--- /dev/null
+++ b/tests/ui/borrowck/issue-62387-suggest-iter-mut-2.fixed
@@ -0,0 +1,36 @@
+// run-rustfix
+#![allow(unused_mut)]
+#![allow(dead_code)]
+use std::path::PathBuf;
+
+#[derive(Clone)]
+struct Container {
+    things: Vec<PathBuf>,
+}
+
+impl Container {
+    fn things(&mut self) -> &[PathBuf] {
+        &self.things
+    }
+}
+
+// contains containers
+struct ContainerContainer {
+    contained: Vec<Container>,
+}
+
+impl ContainerContainer {
+    fn contained(&self) -> &[Container] {
+        &self.contained
+    }
+
+    fn all_the_things(&mut self) -> &[PathBuf] {
+        let mut vec = self.contained.clone();
+        let _a =
+            vec.iter_mut().flat_map(|container| container.things()).cloned().collect::<Vec<PathBuf>>();
+        //~^ ERROR cannot borrow `*container` as mutable, as it is behind a `&` reference
+        unimplemented!();
+    }
+}
+
+fn main() {}
diff --git a/tests/ui/borrowck/issue-62387-suggest-iter-mut-2.rs b/tests/ui/borrowck/issue-62387-suggest-iter-mut-2.rs
new file mode 100644
index 00000000000..2d0b837a946
--- /dev/null
+++ b/tests/ui/borrowck/issue-62387-suggest-iter-mut-2.rs
@@ -0,0 +1,36 @@
+// run-rustfix
+#![allow(unused_mut)]
+#![allow(dead_code)]
+use std::path::PathBuf;
+
+#[derive(Clone)]
+struct Container {
+    things: Vec<PathBuf>,
+}
+
+impl Container {
+    fn things(&mut self) -> &[PathBuf] {
+        &self.things
+    }
+}
+
+// contains containers
+struct ContainerContainer {
+    contained: Vec<Container>,
+}
+
+impl ContainerContainer {
+    fn contained(&self) -> &[Container] {
+        &self.contained
+    }
+
+    fn all_the_things(&mut self) -> &[PathBuf] {
+        let mut vec = self.contained.clone();
+        let _a =
+            vec.iter().flat_map(|container| container.things()).cloned().collect::<Vec<PathBuf>>();
+        //~^ ERROR cannot borrow `*container` as mutable, as it is behind a `&` reference
+        unimplemented!();
+    }
+}
+
+fn main() {}
diff --git a/tests/ui/borrowck/issue-62387-suggest-iter-mut-2.stderr b/tests/ui/borrowck/issue-62387-suggest-iter-mut-2.stderr
new file mode 100644
index 00000000000..19f194100a1
--- /dev/null
+++ b/tests/ui/borrowck/issue-62387-suggest-iter-mut-2.stderr
@@ -0,0 +1,16 @@
+error[E0596]: cannot borrow `*container` as mutable, as it is behind a `&` reference
+  --> $DIR/issue-62387-suggest-iter-mut-2.rs:30:45
+   |
+LL |             vec.iter().flat_map(|container| container.things()).cloned().collect::<Vec<PathBuf>>();
+   |                                  ---------  ^^^^^^^^^ `container` is a `&` reference, so the data it refers to cannot be borrowed as mutable
+   |                                  |
+   |                                  consider changing this binding's type to be: `&mut Container`
+   |
+help: you may want to use `iter_mut` here
+   |
+LL |             vec.iter_mut().flat_map(|container| container.things()).cloned().collect::<Vec<PathBuf>>();
+   |                 ~~~~~~~~
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0596`.
diff --git a/tests/ui/borrowck/issue-62387-suggest-iter-mut.fixed b/tests/ui/borrowck/issue-62387-suggest-iter-mut.fixed
new file mode 100644
index 00000000000..8bf2625de6d
--- /dev/null
+++ b/tests/ui/borrowck/issue-62387-suggest-iter-mut.fixed
@@ -0,0 +1,30 @@
+// run-rustfix
+#![allow(unused_mut)]
+#![allow(dead_code)]
+
+#[derive(Debug)]
+struct A {
+    a: i32,
+}
+
+impl A {
+    fn double(&mut self) {
+        self.a += self.a
+    }
+}
+
+fn baz() {
+    let mut v = [A { a: 4 }];
+    v.iter_mut().for_each(|a| a.double());
+    //~^ ERROR cannot borrow `*a` as mutable, as it is behind a `&` reference
+    println!("{:?}", v);
+}
+
+fn bar() {
+    let mut v = [A { a: 4 }];
+    v.iter_mut().rev().rev().for_each(|a| a.double());
+    //~^ ERROR cannot borrow `*a` as mutable, as it is behind a `&` reference
+    println!("{:?}", v);
+}
+
+fn main() {}
diff --git a/tests/ui/borrowck/issue-62387-suggest-iter-mut.rs b/tests/ui/borrowck/issue-62387-suggest-iter-mut.rs
new file mode 100644
index 00000000000..39bc30bf294
--- /dev/null
+++ b/tests/ui/borrowck/issue-62387-suggest-iter-mut.rs
@@ -0,0 +1,30 @@
+// run-rustfix
+#![allow(unused_mut)]
+#![allow(dead_code)]
+
+#[derive(Debug)]
+struct A {
+    a: i32,
+}
+
+impl A {
+    fn double(&mut self) {
+        self.a += self.a
+    }
+}
+
+fn baz() {
+    let mut v = [A { a: 4 }];
+    v.iter().for_each(|a| a.double());
+    //~^ ERROR cannot borrow `*a` as mutable, as it is behind a `&` reference
+    println!("{:?}", v);
+}
+
+fn bar() {
+    let mut v = [A { a: 4 }];
+    v.iter().rev().rev().for_each(|a| a.double());
+    //~^ ERROR cannot borrow `*a` as mutable, as it is behind a `&` reference
+    println!("{:?}", v);
+}
+
+fn main() {}
diff --git a/tests/ui/borrowck/issue-62387-suggest-iter-mut.stderr b/tests/ui/borrowck/issue-62387-suggest-iter-mut.stderr
new file mode 100644
index 00000000000..fd58e433020
--- /dev/null
+++ b/tests/ui/borrowck/issue-62387-suggest-iter-mut.stderr
@@ -0,0 +1,29 @@
+error[E0596]: cannot borrow `*a` as mutable, as it is behind a `&` reference
+  --> $DIR/issue-62387-suggest-iter-mut.rs:18:27
+   |
+LL |     v.iter().for_each(|a| a.double());
+   |                        -  ^ `a` is a `&` reference, so the data it refers to cannot be borrowed as mutable
+   |                        |
+   |                        consider changing this binding's type to be: `&mut A`
+   |
+help: you may want to use `iter_mut` here
+   |
+LL |     v.iter_mut().for_each(|a| a.double());
+   |       ~~~~~~~~
+
+error[E0596]: cannot borrow `*a` as mutable, as it is behind a `&` reference
+  --> $DIR/issue-62387-suggest-iter-mut.rs:25:39
+   |
+LL |     v.iter().rev().rev().for_each(|a| a.double());
+   |                                    -  ^ `a` is a `&` reference, so the data it refers to cannot be borrowed as mutable
+   |                                    |
+   |                                    consider changing this binding's type to be: `&mut A`
+   |
+help: you may want to use `iter_mut` here
+   |
+LL |     v.iter_mut().rev().rev().for_each(|a| a.double());
+   |       ~~~~~~~~
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0596`.