gccrs: avoid ICE when canonical path record is missing

This fixes an Internal Compiler Error (ICE) in canonical path resolution
triggered by const-generic expressions containing inline item
definitions (e.g. structs inside const blocks).

Previously, CanonicalPathCtx::get_path unconditionally accessed a
canonical path record via get_record, asserting that such a record
always exists. However, some AST nodes (e.g. inline items inside const
expressions) are not guaranteed to have canonical paths, leading to an
ICE.

Update canonical path lookup to be optional and handle the absence of a
record explicitly, avoiding the assertion failure.

gcc/rust/ChangeLog:

	* resolve/rust-name-resolution-context.h
	(CanonicalPathCtx::get_path): Move implementation to source file.
	(CanonicalPathCtx::get_path_opt): New helper returning an optional
	canonical path.

	* resolve/rust-name-resolution-context.cc
	(CanonicalPathCtx::get_path): Use optional canonical path lookup
	and return empty path instead of asserting on missing records.

Signed-off-by: shreyas-omkar <shreyashegdeplus06@gmail.com>

Author: shreyas-omkar

gcc/rust/resolve/rust-name-resolution-context.cc

@@ -184,6 +184,15 @@ CanonicalPathRecordTraitImpl::as_path (const NameResolutionContext &ctx)
       impl_id, trait_path_record.as_path (ctx), type_record.as_path (ctx)));
 }
 
+Resolver::CanonicalPath
+CanonicalPathCtx::get_path (NodeId id) const
+{
+  if (auto rec = get_record_opt (id))
+    return (*rec)->as_path (*nr_ctx);
+
+  return Resolver::CanonicalPath::create_empty ();
+}
+
 NameResolutionContext::NameResolutionContext ()
   : mappings (Analysis::Mappings::get ()), canonical_ctx (*this)
 {}

gcc/rust/resolve/rust-name-resolution-context.h

@@ -359,10 +359,7 @@ class CanonicalPathCtx
     : current_record (nullptr), nr_ctx (&ctx)
   {}
 
-  Resolver::CanonicalPath get_path (NodeId id) const
-  {
-    return get_record (id).as_path (*nr_ctx);
-  }
+  Resolver::CanonicalPath get_path (NodeId id) const;
 
   CanonicalPathRecord &get_record (NodeId id) const
   {
@@ -380,6 +377,14 @@ class CanonicalPathCtx
       return it->second.get ();
   }
 
+  tl::optional<Resolver::CanonicalPath> get_path_opt (NodeId id) const
+  {
+    auto rec = get_record_opt (id);
+    if (!rec)
+      return tl::nullopt;
+    return (*rec)->as_path (*nr_ctx);
+  }
+
   void insert_record (NodeId id, const Identifier &ident)
   {
     insert_record (id, ident.as_string ());

gcc/testsuite/rust/compile/issue-4143.rs

@@ -0,0 +1,19 @@
+// { dg-do compile }
+// { dg-options "-frust-incomplete-and-experimental-compiler-do-not-use" }
+// { dg-prune-output "failed to locate crate" }
+// { dg-prune-output "unknown crate" }
+
+// ICE regression test for canonical path lookup
+// Inline items inside const generic block expressions
+// must not require canonical paths.
+
+struct Expr<const N: u32>;
+
+trait Trait0 {
+    fn required(_: Expr<{
+        struct Type;
+        0
+    }>);
+}
+
+fn main() {}