Do not attempt to compute size of a type with escaping lifetimes

A type with escaping bound vars cannot be wrapped in a dummy binder
during size computation.

Author: samueltardieu

clippy_lints/src/zero_sized_map_values.rs

@@ -56,6 +56,9 @@ impl LateLintPass<'_> for ZeroSizedMapValues {
             // cannot check if it is `Sized` or not, such as an incomplete associated type in a
             // type alias. See an example in `issue14822()` of `tests/ui/zero_sized_hashmap_values.rs`.
             && !ty.has_non_region_param()
+            // Ensure that no region escapes to avoid an assertion error when computing the layout.
+            // See an example in `issue15429()` of `tests/ui/zero_sized_hashmap_values.rs`.
+            && !ty.has_escaping_bound_vars()
             && let Ok(layout) = cx.layout_of(ty)
             && layout.is_zst()
         {

tests/ui/zero_sized_hashmap_values.rs

@@ -92,6 +92,14 @@ fn issue14822() {
     //~^ zero_sized_map_values
 }
 
+fn issue15429() {
+    struct E<'a>(&'a [E<'a>]);
+
+    // The assertion error happens when the type being evaluated has escaping bound vars
+    // as it cannot be wrapped in a dummy binder during size computation.
+    type F = dyn for<'a> FnOnce(HashMap<u32, E<'a>>) -> u32;
+}
+
 fn main() {
     let _: HashMap<String, ()> = HashMap::new();
     //~^ zero_sized_map_values

tests/ui/zero_sized_hashmap_values.stderr

@@ -89,23 +89,23 @@ LL |     type D = HashMap<u32, S<E>>;
    = help: consider using a set instead
 
 error: map with zero-sized value type
-  --> tests/ui/zero_sized_hashmap_values.rs:96:34
+  --> tests/ui/zero_sized_hashmap_values.rs:104:34
    |
 LL |     let _: HashMap<String, ()> = HashMap::new();
    |                                  ^^^^^^^
    |
    = help: consider using a set instead
 
 error: map with zero-sized value type
-  --> tests/ui/zero_sized_hashmap_values.rs:96:12
+  --> tests/ui/zero_sized_hashmap_values.rs:104:12
    |
 LL |     let _: HashMap<String, ()> = HashMap::new();
    |            ^^^^^^^^^^^^^^^^^^^
    |
    = help: consider using a set instead
 
 error: map with zero-sized value type
-  --> tests/ui/zero_sized_hashmap_values.rs:102:12
+  --> tests/ui/zero_sized_hashmap_values.rs:110:12
    |
 LL |     let _: HashMap<_, _> = std::iter::empty::<(String, ())>().collect();
    |            ^^^^^^^^^^^^^