[gccrs COMMIT 1/2] gccrs: Stop method selection when we hit generic params

[gerris.rs@gmail.com]

From: Philip Herron <herron.philip@googlemail.com>

Generics like this need to match directly via their associated type bound
predicates which will already be checked. Otherwise the unify machinery for
types_compatable will wrongly match by injecting infer_vars.

Fixes Rust-GCC/gccrs#4859

gcc/rust/ChangeLog:

	* typecheck/rust-hir-dot-operator.cc (MethodResolver::select): stop on ParamTypes

gcc/testsuite/ChangeLog:

	* rust/compile/issue-4859.rs: New test.

Signed-off-by: Philip Herron <herron.philip@googlemail.com>
---
This change was merged into the gccrs repository and is posted here for
upstream visibility and potential drive-by review, as requested by GCC
release managers.
Each commit email contains a link to its details on github from where you can
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Commit on github: https://github.com/Rust-GCC/gccrs/commit/5d08520e4784bf5898d077c984c4e93577987e1b

The commit has been mentioned in the following issue(s):
 - Rust-GCC/gccrs#4859: https://github.com/Rust-GCC/gccrs/issues/4859

The commit has been mentioned in the following pull-request(s):
 - https://github.com/Rust-GCC/gccrs/pull/4870

 gcc/rust/typecheck/rust-hir-dot-operator.cc |  5 +++
 gcc/testsuite/rust/compile/issue-4859.rs    | 35 +++++++++++++++++++++
 2 files changed, 40 insertions(+)
 create mode 100644 gcc/testsuite/rust/compile/issue-4859.rs

diff --git a/gcc/rust/typecheck/rust-hir-dot-operator.cc b/gcc/rust/typecheck/rust-hir-dot-operator.cc
index 8fd7f1d00..06d9aa88e 100644
--- a/gcc/rust/typecheck/rust-hir-dot-operator.cc
+++ b/gcc/rust/typecheck/rust-hir-dot-operator.cc
@@ -482,6 +482,11 @@ MethodResolver::select (TyTy::BaseType &receiver)
   if (try_select_predicate_candidates (receiver))
     return true;
 
+  // A receiver that is still a bare unresolved generic type parameter can only
+  // ever satisfy a method through its own trait bounds
+  if (receiver.destructure ()->get_kind () == TyTy::TypeKind::PARAM)
+    return false;
+
   // Assemble candidates
   std::vector<impl_item_candidate> inherent_impl_fns;
   if (specified_trait == nullptr)
diff --git a/gcc/testsuite/rust/compile/issue-4859.rs b/gcc/testsuite/rust/compile/issue-4859.rs
new file mode 100644
index 000000000..0be1db8e9
--- /dev/null
+++ b/gcc/testsuite/rust/compile/issue-4859.rs
@@ -0,0 +1,35 @@
+#![feature(no_core, lang_items)]
+#![no_core]
+#[lang = "sized"]
+pub trait Sized {}
+#[lang = "deref"]
+pub trait Deref {
+    type Target: ?Sized;
+    fn deref(&self) -> &Self::Target;
+}
+pub struct VaList {
+    pub inner: i32,
+}
+impl Deref for VaList {
+    type Target = i32;
+    fn deref(&self) -> &i32 {
+        &self.inner
+    }
+}
+pub struct Pin<P> {
+    pub pointer: P,
+}
+impl<P: Deref> Pin<P> {
+    pub const unsafe fn new_unchecked(pointer: P) -> Pin<P> {
+        Pin { pointer }
+    }
+    pub fn as_ref(&self) -> Pin<&P::Target> {
+        unsafe { Pin::new_unchecked(&*self.pointer) }
+    }
+}
+impl<T: ?Sized> Deref for &T {
+    type Target = T;
+    fn deref(&self) -> &T {
+        *self
+    }
+}

base-commit: 4c3e9d122ea17aec02fcad266c36e958ddaa0b12
-- 
2.55.0