Tests illustrating the bug fixes for #27282 and #24535.

Author: pnkfelix

src/test/run-pass/issue-24535-allow-mutable-borrow-in-match-guard.rs

@@ -0,0 +1,68 @@
+// 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.
+
+// This test illustrates that under NLL, we can remove our overly
+// conservative approach for disallowing mutations of match inputs.
+
+// See further discussion on rust-lang/rust#24535 and
+// rust-lang/rfcs#1006.
+
+// compile-flags: -Z disable-ast-check-for-mutation-in-guard
+
+#![feature(nll)]
+
+fn main() {
+    rust_issue_24535();
+    rfcs_issue_1006_1();
+    rfcs_issue_1006_2();
+}
+
+fn rust_issue_24535() {
+    fn compare(a: &u8, b: &mut u8) -> bool {
+        a == b
+    }
+
+    let a = 3u8;
+
+    match a {
+        0 => panic!("nope"),
+        3 if compare(&a, &mut 3) => (),
+        _ => panic!("nope"),
+    }
+}
+
+fn rfcs_issue_1006_1() {
+    let v = vec!["1".to_string(), "2".to_string(), "3".to_string()];
+    match Some(&v) {
+        Some(iv) if iv.iter().any(|x| &x[..]=="2") => true,
+        _ => panic!("nope"),
+    };
+}
+
+fn rfcs_issue_1006_2() {
+    #[inline(always)]
+    fn check<'a, I: Iterator<Item=&'a i32>>(mut i: I) -> bool {
+        i.any(|&x| x == 2)
+    }
+
+    let slice = [1, 2, 3];
+
+    match 42 {
+        _ if slice.iter().any(|&x| x == 2) => { true },
+        _ => { panic!("nope"); }
+    };
+
+    // (This match is just illustrating how easy it was to circumvent
+    // the checking performed for the previous `match`.)
+    match 42 {
+        _ if check(slice.iter()) => { true },
+        _ => { panic!("nope"); }
+    };
+}

src/test/ui/issue-27282-move-match-input-into-guard.rs

@@ -0,0 +1,33 @@
+// 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.
+
+// Issue 27282: Example 2: This sidesteps the AST checks disallowing
+// mutable borrows in match guards by hiding the mutable borrow in a
+// guard behind a move (of the mutably borrowed match input) within a
+// closure.
+//
+// This example is not rejected by AST borrowck (and then reliably
+// reaches the panic code when executed, despite the compiler warning
+// about that match arm being unreachable.
+
+#![feature(nll)]
+
+fn main() {
+    let b = &mut true;
+    match b {
+        &mut false => {},
+        _ if { (|| { let bar = b; *bar = false; })();
+                     //~^ ERROR cannot move out of `b` because it is borrowed [E0505]
+                     false } => { },
+        &mut true => { println!("You might think we should get here"); },
+        //~^ ERROR use of moved value: `*b` [E0382]
+        _ => panic!("surely we could never get here, since rustc warns it is unreachable."),
+    }
+}

src/test/ui/issue-27282-move-match-input-into-guard.stderr

@@ -0,0 +1,32 @@
+error[E0505]: cannot move out of `b` because it is borrowed
+  --> $DIR/issue-27282-move-match-input-into-guard.rs:26:16
+   |
+LL |        match b {
+   |   _____-
+   |  |_____|
+   | ||
+LL | ||         &mut false => {},
+LL | ||         _ if { (|| { let bar = b; *bar = false; })();
+   | ||                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ move out of `b` occurs here
+LL | ||                      //~^ ERROR cannot move out of `b` because it is borrowed [E0505]
+...  ||
+LL | ||         _ => panic!("surely we could never get here, since rustc warns it is unreachable."),
+LL | ||     }
+   | ||     -
+   | ||_____|
+   | |______borrow of `b` occurs here
+   |        borrow later used here
+
+error[E0382]: use of moved value: `*b`
+  --> $DIR/issue-27282-move-match-input-into-guard.rs:29:14
+   |
+LL |         _ if { (|| { let bar = b; *bar = false; })();
+   |                ----------------------------------- value moved here
+...
+LL |         &mut true => { println!("You might think we should get here"); },
+   |              ^^^^ value used here after move
+
+error: aborting due to 2 previous errors
+
+Some errors occurred: E0382, E0505.
+For more information about an error, try `rustc --explain E0382`.

src/test/ui/issue-27282-move-ref-mut-into-guard.rs

@@ -0,0 +1,28 @@
+// 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.
+
+// Issue 27282: Example 1: This sidesteps the AST checks disallowing
+// mutable borrows in match guards by hiding the mutable borrow in a
+// guard behind a move (of the ref mut pattern id) within a closure.
+//
+// This example is not rejected by AST borrowck (and then reliably
+// segfaults when executed).
+
+#![feature(nll)]
+
+fn main() {
+    match Some(&4) {
+        None => {},
+        ref mut foo
+            if { (|| { let bar = foo; bar.take() })(); false } => {},
+        //~^ ERROR cannot move out of borrowed content [E0507]
+        Some(s) => std::process::exit(*s),
+    }
+}

src/test/ui/issue-27282-move-ref-mut-into-guard.stderr

@@ -0,0 +1,9 @@
+error[E0507]: cannot move out of borrowed content
+  --> $DIR/issue-27282-move-ref-mut-into-guard.rs:24:18
+   |
+LL |             if { (|| { let bar = foo; bar.take() })(); false } => {},
+   |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot move out of borrowed content
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0507`.

src/test/ui/issue-27282-reborrow-ref-mut-in-guard.rs

@@ -0,0 +1,32 @@
+// 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.
+
+// Issue 27282: This is a variation on issue-27282-move-ref-mut-into-guard.rs
+//
+// It reborrows instead of moving the `ref mut` pattern borrow. This
+// means that our conservative check for mutation in guards will
+// reject it. But I want to make sure that we continue to reject it
+// (under NLL) even when that conservaive check goes away.
+
+// compile-flags: -Z disable-ast-check-for-mutation-in-guard
+
+#![feature(nll)]
+
+fn main() {
+    let mut b = &mut true;
+    match b {
+        &mut false => {},
+        ref mut r if { (|| { let bar = &mut *r; **bar = false; })();
+                             //~^ ERROR cannot borrow immutable item `*r` as mutable
+                             false } => { &mut *r; },
+        &mut true => { println!("You might think we should get here"); },
+        _ => panic!("surely we could never get here, since rustc warns it is unreachable."),
+    }
+}

src/test/ui/issue-27282-reborrow-ref-mut-in-guard.stderr

@@ -0,0 +1,9 @@
+error[E0596]: cannot borrow immutable item `*r` as mutable
+  --> $DIR/issue-27282-reborrow-ref-mut-in-guard.rs:26:24
+   |
+LL |         ref mut r if { (|| { let bar = &mut *r; **bar = false; })();
+   |                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot borrow as mutable
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0596`.