Test cases for handling mutable references

src/test/ui/closures/2229_closure_analysis/diagnostics/cant-mutate-imm-borrow.rs

@@ -0,0 +1,21 @@
+// Test that if we deref an immutable borrow to access a Place,
+// then we can't mutate the final place.
+
+#![feature(capture_disjoint_fields)]
+//~^ WARNING: the feature `capture_disjoint_fields` is incomplete
+
+fn main() {
+    let mut x = (format!(""), format!("X2"));
+    let mut y = (&x, "Y");
+    let z = (&mut y, "Z");
+
+    // `x.0` is mutable but we access `x` via `z.0.0`, which is an immutable reference and
+    // therefore can't be mutated.
+    let mut c = || {
+    //~^ ERROR: cannot borrow `z.0.0.0` as mutable, as it is behind a `&` reference
+        z.0.0.0 = format!("X1");
+        //~^ ERROR: cannot assign to `z`, as it is not declared as mutable
+    };
+
+    c();
+}

src/test/ui/closures/2229_closure_analysis/diagnostics/cant-mutate-imm-borrow.stderr

@@ -0,0 +1,31 @@
+warning: the feature `capture_disjoint_fields` is incomplete and may not be safe to use and/or cause compiler crashes
+  --> $DIR/cant-mutate-imm-borrow.rs:4:12
+   |
+LL | #![feature(capture_disjoint_fields)]
+   |            ^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: `#[warn(incomplete_features)]` on by default
+   = note: see issue #53488 <https://github.com/rust-lang/rust/issues/53488> for more information
+
+error[E0594]: cannot assign to `z`, as it is not declared as mutable
+  --> $DIR/cant-mutate-imm-borrow.rs:16:9
+   |
+LL |     let z = (&mut y, "Z");
+   |         - help: consider changing this to be mutable: `mut z`
+...
+LL |         z.0.0.0 = format!("X1");
+   |         ^^^^^^^ cannot assign
+
+error[E0596]: cannot borrow `z.0.0.0` as mutable, as it is behind a `&` reference
+  --> $DIR/cant-mutate-imm-borrow.rs:14:17
+   |
+LL |     let mut c = || {
+   |                 ^^ cannot borrow as mutable
+LL |
+LL |         z.0.0.0 = format!("X1");
+   |         - mutable borrow occurs due to use of `z.0.0.0` in closure
+
+error: aborting due to 2 previous errors; 1 warning emitted
+
+Some errors have detailed explanations: E0594, E0596.
+For more information about an error, try `rustc --explain E0594`.

src/test/ui/closures/2229_closure_analysis/diagnostics/mut_ref.rs

@@ -0,0 +1,40 @@
+// Test that we can't mutate a place if we need to deref an imm-borrow
+// to reach it.
+
+#![feature(capture_disjoint_fields)]
+//~^ WARNING: the feature `capture_disjoint_fields` is incomplete
+
+fn imm_mut_ref() {
+    let mut x = String::new();
+    let y = String::new();
+    let mref_x = &mut x;
+    let ref_mref_x = &mref_x;
+
+    let c = || {
+    //~^ ERROR: cannot borrow `**ref_mref_x` as mutable, as it is behind a `&` reference
+        **ref_mref_x = y;
+        //~^ERROR: cannot assign to `ref_mref_x`, as it is not declared as mutable
+    };
+
+    c();
+}
+
+fn mut_imm_ref() {
+    let x = String::new();
+    let y = String::new();
+    let mut ref_x = &x;
+    let mref_ref_x = &mut ref_x;
+
+    let c = || {
+    //~^ ERROR: cannot borrow `**mref_ref_x` as mutable, as it is behind a `&` reference
+        **mref_ref_x = y;
+        //~^ERROR: cannot assign to `mref_ref_x`, as it is not declared as mutable
+    };
+
+    c();
+}
+
+fn main() {
+    imm_mut_ref();
+    mut_imm_ref();
+}

src/test/ui/closures/2229_closure_analysis/diagnostics/mut_ref.stderr

@@ -0,0 +1,52 @@
+warning: the feature `capture_disjoint_fields` is incomplete and may not be safe to use and/or cause compiler crashes
+  --> $DIR/mut_ref.rs:4:12
+   |
+LL | #![feature(capture_disjoint_fields)]
+   |            ^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: `#[warn(incomplete_features)]` on by default
+   = note: see issue #53488 <https://github.com/rust-lang/rust/issues/53488> for more information
+
+error[E0594]: cannot assign to `ref_mref_x`, as it is not declared as mutable
+  --> $DIR/mut_ref.rs:15:9
+   |
+LL |     let ref_mref_x = &mref_x;
+   |         ---------- help: consider changing this to be mutable: `mut ref_mref_x`
+...
+LL |         **ref_mref_x = y;
+   |         ^^^^^^^^^^^^ cannot assign
+
+error[E0596]: cannot borrow `**ref_mref_x` as mutable, as it is behind a `&` reference
+  --> $DIR/mut_ref.rs:13:13
+   |
+LL |     let ref_mref_x = &mref_x;
+   |                      ------- help: consider changing this to be a mutable reference: `&mut mref_x`
+LL | 
+LL |     let c = || {
+   |             ^^ `ref_mref_x` is a `&` reference, so the data it refers to cannot be borrowed as mutable
+LL |
+LL |         **ref_mref_x = y;
+   |           ---------- mutable borrow occurs due to use of `**ref_mref_x` in closure
+
+error[E0594]: cannot assign to `mref_ref_x`, as it is not declared as mutable
+  --> $DIR/mut_ref.rs:30:9
+   |
+LL |     let mref_ref_x = &mut ref_x;
+   |         ---------- help: consider changing this to be mutable: `mut mref_ref_x`
+...
+LL |         **mref_ref_x = y;
+   |         ^^^^^^^^^^^^ cannot assign
+
+error[E0596]: cannot borrow `**mref_ref_x` as mutable, as it is behind a `&` reference
+  --> $DIR/mut_ref.rs:28:13
+   |
+LL |     let c = || {
+   |             ^^ cannot borrow as mutable
+LL |
+LL |         **mref_ref_x = y;
+   |           ---------- mutable borrow occurs due to use of `**mref_ref_x` in closure
+
+error: aborting due to 4 previous errors; 1 warning emitted
+
+Some errors have detailed explanations: E0594, E0596.
+For more information about an error, try `rustc --explain E0594`.

src/test/ui/closures/2229_closure_analysis/run_pass/mut_ref.rs

@@ -0,0 +1,56 @@
+// run-pass
+
+// Test that we can mutate a place through a mut-borrow
+// that is captured by the closure
+
+#![feature(capture_disjoint_fields)]
+//~^ WARNING: the feature `capture_disjoint_fields` is incomplete
+
+// Check that we can mutate when one deref is required
+fn mut_ref_1() {
+    let mut x = String::new();
+    let rx = &mut x;
+
+    let mut c = || {
+        *rx = String::new();
+    };
+
+    c();
+}
+
+// Similar example as mut_ref_1, we don't deref the imm-borrow here,
+// and so we are allowed to mutate.
+fn mut_ref_2() {
+    let x = String::new();
+    let y = String::new();
+    let mut ref_x = &x;
+    let m_ref_x = &mut ref_x;
+
+    let mut c = || {
+        *m_ref_x = &y;
+    };
+
+    c();
+}
+
+// Check that we can mutate when multiple derefs of mut-borrows are required to reach
+// the target place.
+// It works because all derefs are mutable, if either of them was an immutable
+// borrow, then we would not be able to deref.
+fn mut_mut_ref() {
+    let mut x = String::new();
+    let mut mref_x = &mut x;
+    let m_mref_x = &mut mref_x;
+
+    let mut c = || {
+        **m_mref_x = String::new();
+    };
+
+    c();
+}
+
+fn main() {
+    mut_ref_1();
+    mut_ref_2();
+    mut_mut_ref();
+}

src/test/ui/closures/2229_closure_analysis/run_pass/mut_ref.stderr

@@ -0,0 +1,11 @@
+warning: the feature `capture_disjoint_fields` is incomplete and may not be safe to use and/or cause compiler crashes
+  --> $DIR/mut_ref.rs:6:12
+   |
+LL | #![feature(capture_disjoint_fields)]
+   |            ^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: `#[warn(incomplete_features)]` on by default
+   = note: see issue #53488 <https://github.com/rust-lang/rust/issues/53488> for more information
+
+warning: 1 warning emitted
+

src/test/ui/closures/2229_closure_analysis/run_pass/mut_ref_struct_mem.rs

@@ -0,0 +1,23 @@
+// run-pass
+
+// Test that we can mutate a place through a mut-borrow
+// that is captured by the closure
+//
+// More specifically we test that the if the mutable reference isn't root variable of a capture
+// but rather accessed while acessing the precise capture.
+
+#![feature(capture_disjoint_fields)]
+//~^ WARNING: the feature `capture_disjoint_fields` is incomplete
+
+fn main() {
+    let mut t = (10, 10);
+
+    let t1 = (&mut t, 10);
+
+    let mut c = || {
+        // Mutable because (*t.0) is mutable
+        t1.0.0 += 10;
+    };
+
+    c();
+}

src/test/ui/closures/2229_closure_analysis/run_pass/mut_ref_struct_mem.stderr

@@ -0,0 +1,11 @@
+warning: the feature `capture_disjoint_fields` is incomplete and may not be safe to use and/or cause compiler crashes
+  --> $DIR/mut_ref_struct_mem.rs:9:12
+   |
+LL | #![feature(capture_disjoint_fields)]
+   |            ^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: `#[warn(incomplete_features)]` on by default
+   = note: see issue #53488 <https://github.com/rust-lang/rust/issues/53488> for more information
+
+warning: 1 warning emitted
+