Fix ICE while computing type layout (#14837)

If a type is incomplete, for example if generic parameters are not
available yet, although they are not escaping, its layout may not be
computable. Calling `TyCtxt::layout_of()` would create a delayed bug in
the compiler.

changelog: [`zero_sized_map_values`]: fix ICE

Fixes #14822

r? @Jarcho

Author: Jarcho

clippy_lints/src/zero_sized_map_values.rs

@@ -51,9 +51,11 @@ impl LateLintPass<'_> for ZeroSizedMapValues {
             && (is_type_diagnostic_item(cx, ty, sym::HashMap) || is_type_diagnostic_item(cx, ty, sym::BTreeMap))
             && let ty::Adt(_, args) = ty.kind()
             && let ty = args.type_at(1)
-            // Fixes https://github.com/rust-lang/rust-clippy/issues/7447 because of
-            // https://github.com/rust-lang/rust/blob/master/compiler/rustc_middle/src/ty/sty.rs#L968
-            && !ty.has_escaping_bound_vars()
+            // Ensure that no type information is missing, to avoid a delayed bug in the compiler if this is not the case.
+            // This might happen when computing a reference/pointer metadata on a type for which we
+            // 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()
             && let Ok(layout) = cx.layout_of(ty)
             && layout.is_zst()
         {

tests/ui/crashes/ice-6840.rs

@@ -2,6 +2,7 @@
 //! This is a reproducer for the ICE 6840: https://github.com/rust-lang/rust-clippy/issues/6840.
 //! The ICE is caused by `TyCtxt::layout_of` and `is_normalizable` not being strict enough
 #![allow(dead_code)]
+#![deny(clippy::zero_sized_map_values)] // For ICE 14822
 use std::collections::HashMap;
 
 pub trait Rule {

tests/ui/zero_sized_hashmap_values.rs

@@ -71,6 +71,27 @@ fn test2(map: HashMap<String, usize>, key: &str) -> HashMap<String, usize> {
     todo!();
 }
 
+fn issue14822() {
+    trait Trait {
+        type T;
+    }
+    struct S<T: Trait>(T::T);
+
+    // The `delay_bug` happens when evaluating the pointer metadata of `S<T>` which depends on
+    // whether `T::T` is `Sized`. Since the type alias doesn't have a trait bound of `T: Trait`
+    // evaluating `T::T: Sized` ultimately fails with `NoSolution`.
+    type A<T> = HashMap<u32, *const S<T>>;
+    type B<T> = HashMap<u32, S<T>>;
+
+    enum E {}
+    impl Trait for E {
+        type T = ();
+    }
+    type C = HashMap<u32, *const S<E>>;
+    type D = HashMap<u32, S<E>>;
+    //~^ zero_sized_map_values
+}
+
 fn main() {
     let _: HashMap<String, ()> = HashMap::new();
     //~^ zero_sized_map_values

tests/ui/zero_sized_hashmap_values.stderr

@@ -81,28 +81,36 @@ LL | fn test(map: HashMap<String, ()>, key: &str) -> HashMap<String, ()> {
    = help: consider using a set instead
 
 error: map with zero-sized value type
-  --> tests/ui/zero_sized_hashmap_values.rs:75:34
+  --> tests/ui/zero_sized_hashmap_values.rs:91:14
+   |
+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
    |
 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:75:12
+  --> tests/ui/zero_sized_hashmap_values.rs:96:12
    |
 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:81:12
+  --> tests/ui/zero_sized_hashmap_values.rs:102:12
    |
 LL |     let _: HashMap<_, _> = std::iter::empty::<(String, ())>().collect();
    |            ^^^^^^^^^^^^^
    |
    = help: consider using a set instead
 
-error: aborting due to 13 previous errors
+error: aborting due to 14 previous errors