Auto merge of #54490 - wesleywiser:rewrite_it_in_mir, r=oli-obk

Rewrite the `UnconditionalRecursion` lint to use MIR

Part of #51002

r? @eddyb

src/test/ui/did_you_mean/issue-31424.nll.stderr

@@ -7,8 +7,20 @@ LL |         (&mut self).bar(); //~ ERROR cannot borrow
    |         cannot borrow as mutable
    |         try removing `&mut` here
 
+warning: function cannot return without recursing
+  --> $DIR/issue-31424.rs:22:5
+   |
+LL |     fn bar(self: &mut Self) {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^ cannot return without recursing
+LL |         //~^ WARN function cannot return without recursing
+LL |         (&mut self).bar(); //~ ERROR cannot borrow
+   |         ----------------- recursive call site
+   |
+   = note: #[warn(unconditional_recursion)] on by default
+   = help: a `loop` may express intention better if this is on purpose
+
 error[E0596]: cannot borrow `self` as mutable, as it is not declared as mutable
-  --> $DIR/issue-31424.rs:23:9
+  --> $DIR/issue-31424.rs:24:9
    |
 LL |         (&mut self).bar(); //~ ERROR cannot borrow
    |         ^^^^^^^^^^^

src/test/ui/did_you_mean/issue-31424.rs

@@ -20,6 +20,7 @@ impl Struct {
     // In this case we could keep the suggestion, but to distinguish the
     // two cases is pretty hard. It's an obscure case anyway.
     fn bar(self: &mut Self) {
+        //~^ WARN function cannot return without recursing
         (&mut self).bar(); //~ ERROR cannot borrow
     }
 }

src/test/ui/did_you_mean/issue-31424.stderr

@@ -7,8 +7,20 @@ LL |         (&mut self).bar(); //~ ERROR cannot borrow
    |               cannot reborrow mutably
    |               try removing `&mut` here
 
+warning: function cannot return without recursing
+  --> $DIR/issue-31424.rs:22:5
+   |
+LL |     fn bar(self: &mut Self) {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^ cannot return without recursing
+LL |         //~^ WARN function cannot return without recursing
+LL |         (&mut self).bar(); //~ ERROR cannot borrow
+   |         ----------------- recursive call site
+   |
+   = note: #[warn(unconditional_recursion)] on by default
+   = help: a `loop` may express intention better if this is on purpose
+
 error[E0596]: cannot borrow immutable argument `self` as mutable
-  --> $DIR/issue-31424.rs:23:15
+  --> $DIR/issue-31424.rs:24:15
    |
 LL |         (&mut self).bar(); //~ ERROR cannot borrow
    |               ^^^^ cannot borrow mutably

src/test/ui/nll/issue-51191.rs

@@ -14,6 +14,7 @@ struct Struct;
 
 impl Struct {
     fn bar(self: &mut Self) {
+        //~^ WARN function cannot return without recursing
         (&mut self).bar();
         //~^ ERROR cannot borrow `self` as mutable, as it is not declared as mutable [E0596]
     }

src/test/ui/nll/issue-51191.stderr

@@ -1,5 +1,17 @@
+warning: function cannot return without recursing
+  --> $DIR/issue-51191.rs:16:5
+   |
+LL |     fn bar(self: &mut Self) {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^ cannot return without recursing
+LL |         //~^ WARN function cannot return without recursing
+LL |         (&mut self).bar();
+   |         ----------------- recursive call site
+   |
+   = note: #[warn(unconditional_recursion)] on by default
+   = help: a `loop` may express intention better if this is on purpose
+
 error[E0596]: cannot borrow `self` as mutable, as it is not declared as mutable
-  --> $DIR/issue-51191.rs:17:9
+  --> $DIR/issue-51191.rs:18:9
    |
 LL |         (&mut self).bar();
    |         ^^^^^^^^^^^
@@ -8,7 +20,7 @@ LL |         (&mut self).bar();
    |         try removing `&mut` here
 
 error[E0596]: cannot borrow `self` as mutable, as it is not declared as mutable
-  --> $DIR/issue-51191.rs:22:9
+  --> $DIR/issue-51191.rs:23:9
    |
 LL |     fn imm(self) {
    |            ---- help: consider changing this to be mutable: `mut self`
@@ -16,19 +28,19 @@ LL |         (&mut self).bar();
    |         ^^^^^^^^^^^ cannot borrow as mutable
 
 error[E0596]: cannot borrow `self` as mutable, as it is not declared as mutable
-  --> $DIR/issue-51191.rs:31:9
+  --> $DIR/issue-51191.rs:32:9
    |
 LL |         (&mut self).bar();
    |         ^^^^^^^^^^^ cannot borrow as mutable
 
 error[E0596]: cannot borrow data in a `&` reference as mutable
-  --> $DIR/issue-51191.rs:31:9
+  --> $DIR/issue-51191.rs:32:9
    |
 LL |         (&mut self).bar();
    |         ^^^^^^^^^^^ cannot borrow as mutable
 
 error[E0596]: cannot borrow `self` as mutable, as it is not declared as mutable
-  --> $DIR/issue-51191.rs:37:9
+  --> $DIR/issue-51191.rs:38:9
    |
 LL |         (&mut self).bar();
    |         ^^^^^^^^^^^

src/test/ui/regions/region-bound-on-closure-outlives-call.nll.stderr

@@ -1,5 +1,17 @@
+warning: function cannot return without recursing
+  --> $DIR/region-bound-on-closure-outlives-call.rs:11:1
+   |
+LL | fn call_rec<F>(mut f: F) -> usize where F: FnMut(usize) -> usize {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot return without recursing
+LL |     //~^ WARN function cannot return without recursing
+LL |     (|x| f(x))(call_rec(f)) //~ ERROR cannot move out of `f`
+   |                ----------- recursive call site
+   |
+   = note: #[warn(unconditional_recursion)] on by default
+   = help: a `loop` may express intention better if this is on purpose
+
 error[E0505]: cannot move out of `f` because it is borrowed
-  --> $DIR/region-bound-on-closure-outlives-call.rs:12:25
+  --> $DIR/region-bound-on-closure-outlives-call.rs:13:25
    |
 LL |     (|x| f(x))(call_rec(f)) //~ ERROR cannot move out of `f`
    |     ----------          ^ move out of `f` occurs here

src/test/ui/regions/region-bound-on-closure-outlives-call.rs

@@ -9,6 +9,7 @@
 // except according to those terms.
 
 fn call_rec<F>(mut f: F) -> usize where F: FnMut(usize) -> usize {
+    //~^ WARN function cannot return without recursing
     (|x| f(x))(call_rec(f)) //~ ERROR cannot move out of `f`
 }
 

src/test/ui/regions/region-bound-on-closure-outlives-call.stderr

@@ -1,5 +1,17 @@
+warning: function cannot return without recursing
+  --> $DIR/region-bound-on-closure-outlives-call.rs:11:1
+   |
+LL | fn call_rec<F>(mut f: F) -> usize where F: FnMut(usize) -> usize {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot return without recursing
+LL |     //~^ WARN function cannot return without recursing
+LL |     (|x| f(x))(call_rec(f)) //~ ERROR cannot move out of `f`
+   |                ----------- recursive call site
+   |
+   = note: #[warn(unconditional_recursion)] on by default
+   = help: a `loop` may express intention better if this is on purpose
+
 error[E0505]: cannot move out of `f` because it is borrowed
-  --> $DIR/region-bound-on-closure-outlives-call.rs:12:25
+  --> $DIR/region-bound-on-closure-outlives-call.rs:13:25
    |
 LL |     (|x| f(x))(call_rec(f)) //~ ERROR cannot move out of `f`
    |      ---                ^ move out of `f` occurs here