(c2rust-analyze) Add complete dataflow constraints for `CastKind::P…

…ointer` (previously incomplete).

More tests have also been added to `string_casts.rs`
exercising as many of the `PointerCast`s as possible,
but many of these crash later on, so they're disabled.

c2rust-analyze/src/dataflow/type_check.rs

@@ -13,6 +13,7 @@ use rustc_middle::mir::{
 };
 use rustc_middle::ty::adjustment::PointerCast;
 use rustc_middle::ty::{SubstsRef, Ty, TyKind};
+use std::iter;
 
 /// Visitor that walks over the MIR, computing types of rvalues/operands/places and generating
 /// constraints as a side effect.
@@ -135,8 +136,30 @@ impl<'tcx> TypeChecker<'tcx, '_> {
                     PointerCast::ArrayToPointer => {}
                     PointerCast::Unsize => {}
                 }
-                self.do_assign_pointer_ids(to_lty.label, from_lty.label)
-                // TODO add other dataflow constraints
+
+                // We would normally do `self.do_assign`,
+                // but we can't do a normal `self.do_equivalence_nested` (inside `self.do_assign`),
+                // so we do the `self.do_assign_pointer_ids` from `self.do_assign`,
+                // and then do the body of `self.do_equivalence_nested`,
+                // but after the extra outer layers are stripped.
+
+                self.do_assign_pointer_ids(to_lty.label, from_lty.label);
+
+                // Each of these ptr casts needs at least the outer layer stripped (e.x. `&`, `*mut`, `fn`),
+                // but then after that, these ptr casts below
+                // needs more layers stripped to reach the types that are equivalent.
+                let strip_from = |lty: LTy<'tcx>| match ptr_cast {
+                    PointerCast::ArrayToPointer => lty.args[0],
+                    PointerCast::Unsize => lty.args[0],
+                    _ => lty,
+                };
+                let strip_to = |lty: LTy<'tcx>| match ptr_cast {
+                    PointerCast::Unsize => lty.args[0],
+                    _ => lty,
+                };
+                for (&from_lty, &to_lty) in iter::zip(from_lty.args, to_lty.args) {
+                    self.do_unify(strip_from(from_lty), strip_to(to_lty));
+                }
             }
             CastKind::Misc => {
                 match is_transmutable_ptr_cast(from_ty, to_ty) {

c2rust-analyze/tests/analyze/string_casts.rs

@@ -33,3 +33,57 @@ pub fn cast_from_literal() {
 pub fn cast_from_literal_explicit() {
     std::ptr::addr_of!(*b"\0") as *const u8 as *const core::ffi::c_char;
 }
+
+/// [`PointerCast::ReifyFnPointer`]
+/// Can't figure out how to create a [`PointerCast::ReifyFnPointer`].
+#[cfg(any())]
+pub fn cast_fn_item_to_fn_ptr(f: impl Fn(u8) -> i8) {
+    f as fn(u8) -> i8;
+}
+
+/// [`PointerCast::UnsafeFnPointer`]
+/// 
+/// ```shell
+/// thread 'rustc' panicked at 'not yet implemented', c2rust-analyze/src/labeled_ty.rs:372:17
+/// ```
+#[cfg(any())]
+pub fn cast_fn_ptr_to_unsafe_fn_ptr(f: fn(u8) -> i8) {
+    f as unsafe fn(u8) -> i8;
+}
+
+/// [`PointerCast::ClosureFnPointer`]
+/// Unhandled very early on.
+#[cfg(any())]
+pub fn cast_closure_to_fn_ptr() {
+    (|b: u8| b as i8) as fn(u8) -> i8;
+}
+
+/// [`PointerCast::MutToConstPointer`]
+/// 
+/// ```shell
+/// thread 'rustc' panicked at 'not yet implemented', c2rust-analyze/src/labeled_ty.rs:372:17
+/// ```
+#[cfg(any())]
+pub fn cast_mut_to_const_ptr(p: *mut i32) {
+    p as *const i32;
+}
+
+/// Meant to be [`PointerCast::ArrayToPointer`], but is [`CastKind::Misc`].
+pub fn cast_array_ptr_to_ptr(p: *const [i32; 1]) {
+    p as *const i32;
+}
+
+/// [`PointerCast::Unsize`]
+///
+/// ```shell
+/// thread 'rustc' panicked at 'expected to find only one Assign statement, but got multiple', c2rust-analyze/src/rewrite/expr/hir_op.rs:126:21
+/// ```
+#[cfg(any())]
+pub fn cast_unsize_direct(a: &[i32; 1]) {
+    a as &[i32];
+}
+
+/// [`PointerCast::Unsize`]
+pub fn cast_unsize_indirect(a: &[i32; 1]) {
+    let _ = a.as_ptr();
+}