Auto merge of #72412 - VFLashM:issue-72408-nested-closures-exponential, r=tmandry

Issue 72408 nested closures exponential

This fixes #72408.

Nested closures were resulting in exponential compilation time.

This PR is enhancing asymptotic complexity, but also increasing the constant, so I would love to see perf run results.

src/test/ui/closures/issue-72408-nested-closures-exponential.rs

@@ -0,0 +1,59 @@
+// build-pass
+
+// Closures include captured types twice in a type tree.
+//
+// Wrapping one closure with another leads to doubling
+// the amount of types in the type tree.
+//
+// This test ensures that rust can handle
+// deeply nested type trees with a lot
+// of duplicated subtrees.
+
+fn dup(f: impl Fn(i32) -> i32) -> impl Fn(i32) -> i32 {
+    move |a| f(a * 2)
+}
+
+fn main() {
+    let f = |a| a;
+
+    let f = dup(f);
+    let f = dup(f);
+    let f = dup(f);
+    let f = dup(f);
+    let f = dup(f);
+
+    let f = dup(f);
+    let f = dup(f);
+    let f = dup(f);
+    let f = dup(f);
+    let f = dup(f);
+
+    let f = dup(f);
+    let f = dup(f);
+    let f = dup(f);
+    let f = dup(f);
+    let f = dup(f);
+
+    let f = dup(f);
+    let f = dup(f);
+    let f = dup(f);
+    let f = dup(f);
+    let f = dup(f);
+
+    // Compiler dies around here if it tries
+    // to walk the tree exhaustively.
+
+    let f = dup(f);
+    let f = dup(f);
+    let f = dup(f);
+    let f = dup(f);
+    let f = dup(f);
+
+    let f = dup(f);
+    let f = dup(f);
+    let f = dup(f);
+    let f = dup(f);
+    let f = dup(f);
+
+    println!("Type size was at least {}", f(1));
+}

src/test/ui/infinite/infinite-instantiation.stderr

@@ -1,4 +1,4 @@
-error: reached the recursion limit while instantiating `function::<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<usize>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>`
+error: reached the recursion limit while instantiating `function::<Option<Option<Option<...>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>`
   --> $DIR/infinite-instantiation.rs:21:9
    |
 LL |         function(counter - 1, t.to_option());

src/test/ui/issues/issue-22638.rs

@@ -51,9 +51,9 @@ struct D (Box<A>);
 
 impl D {
     pub fn matches<F: Fn()>(&self, f: &F) {
-        //~^ ERROR reached the type-length limit while instantiating `D::matches::<[closure
         let &D(ref a) = self;
         a.matches(f)
+        //~^ ERROR reached the recursion limit while instantiating `A::matches::<[closure
     }
 }
 

src/test/ui/issues/issue-22638.stderr

@@ -1,10 +1,14 @@
-error: reached the type-length limit while instantiating `D::matches::$CLOSURE`
-  --> $DIR/issue-22638.rs:53:5
+error: reached the recursion limit while instantiating `A::matches::$CLOSURE`
+  --> $DIR/issue-22638.rs:55:9
+   |
+LL |         a.matches(f)
+   |         ^^^^^^^^^^^^
+   |
+note: `A::matches` defined here
+  --> $DIR/issue-22638.rs:14:5
    |
 LL |     pub fn matches<F: Fn()>(&self, f: &F) {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = note: consider adding a `#![type_length_limit="30408681"]` attribute to your crate
 
 error: aborting due to previous error
 

src/test/ui/issues/issue-37311-type-length-limit/issue-37311.rs

@@ -12,8 +12,8 @@ trait Foo {
 
 impl<T> Foo for T {
     #[allow(unconditional_recursion)]
-    fn recurse(&self) { //~ ERROR reached the type-length limit
-        (self, self).recurse();
+    fn recurse(&self) {
+        (self, self).recurse(); //~ ERROR reached the recursion limit
     }
 }
 

src/test/ui/issues/issue-37311-type-length-limit/issue-37311.stderr

@@ -1,10 +1,14 @@
-error: reached the type-length limit while instantiating `<(&(&(&(&(&(&(&(&(&(&(&(&(&(&(&(...))))))))))))))) as Foo>::recurse`
+error: reached the recursion limit while instantiating `<(&(&(&(&(&(&(&(&(&(&(&(&(&(&(&(.....), ...), ...) as Foo>::recurse`
+  --> $DIR/issue-37311.rs:16:9
+   |
+LL |         (self, self).recurse();
+   |         ^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: `<T as Foo>::recurse` defined here
   --> $DIR/issue-37311.rs:15:5
    |
 LL |     fn recurse(&self) {
    |     ^^^^^^^^^^^^^^^^^
-   |
-   = note: consider adding a `#![type_length_limit="2097149"]` attribute to your crate
 
 error: aborting due to previous error
 

src/test/ui/issues/issue-67552.stderr

@@ -1,4 +1,4 @@
-error: reached the recursion limit while instantiating `rec::<&mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut &mut Empty>`
+error: reached the recursion limit while instantiating `rec::<&mut &mut &mut &mut &mut &... &mut &mut &mut &mut &mut Empty>`
   --> $DIR/issue-67552.rs:27:9
    |
 LL |         rec(identity(&mut it))

src/test/ui/issues/issue-8727.stderr

@@ -9,7 +9,7 @@ LL |     generic::<Option<T>>();
    = note: `#[warn(unconditional_recursion)]` on by default
    = help: a `loop` may express intention better if this is on purpose
 
-error: reached the recursion limit while instantiating `generic::<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<Option<i32>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>`
+error: reached the recursion limit while instantiating `generic::<Option<Option<Option<O...>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>`
   --> $DIR/issue-8727.rs:7:5
    |
 LL |     generic::<Option<T>>();

src/test/ui/recursion/issue-38591-non-regular-dropck-recursion.stderr

@@ -1,4 +1,4 @@
-error: reached the recursion limit while instantiating `drop_in_place::<S<fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(u32))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))>> - shim(Some(S<fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(u32))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))>))`
+error: reached the recursion limit while instantiating `drop_in_place::<S<fn(fn(fn(fn(fn...)))))))))))))))))))))))))))))>))`
   --> $SRC_DIR/core/src/ptr/mod.rs:LL:COL
    |
 LL | / pub unsafe fn drop_in_place<T: ?Sized>(to_drop: *mut T) {

src/test/ui/recursion/recursion.stderr

@@ -1,4 +1,4 @@
-error: reached the recursion limit while instantiating `test::<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Cons<Nil>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>`
+error: reached the recursion limit while instantiating `test::<Cons<Cons<Cons<Cons<Cons<...>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>`
   --> $DIR/recursion.rs:17:11
    |
 LL |     _ => {test (n-1, i+1, Cons {head:2*i+1, tail:first}, Cons{head:i*i, tail:second})}

src/test/ui/type_length_limit.rs

@@ -4,7 +4,7 @@
 // Test that the type length limit can be changed.
 
 #![allow(dead_code)]
-#![type_length_limit="256"]
+#![type_length_limit="4"]
 
 macro_rules! link {
     ($id:ident, $t:ty) => {

src/test/ui/type_length_limit.stderr

@@ -1,10 +1,10 @@
-error: reached the type-length limit while instantiating `std::mem::drop::<Option<((((((G,... G), (G, G, G), (G, G, G))))))>>`
+error: reached the type-length limit while instantiating `std::mem::drop::<Option<((((...,....., ...), ..., ...), ..., ...)>>`
   --> $SRC_DIR/core/src/mem/mod.rs:LL:COL
    |
 LL | pub fn drop<T>(_x: T) {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: consider adding a `#![type_length_limit="1094"]` attribute to your crate
+   = note: consider adding a `#![type_length_limit="8"]` attribute to your crate
 
 error: aborting due to previous error