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_record unconditionally asserted that
a canonical path record exists for a NodeId. However, not all AST nodes
(e.g. inline items in const expressions) are guaranteed to have canonical
paths, leading to an ICE.

Introduce optional canonical path lookup and update callers to handle
the absence of a canonical path explicitly, avoiding the assertion
failure.

gcc/rust/ChangeLog:

	* resolve/rust-name-resolution-context.h
	(CanonicalPathCtx::get_path_opt): New helper returning an optional
	canonical path.
	* resolve/rust-name-resolution-context.cc: Use optional canonical
	path lookup instead of asserting on missing records.	* testsuite/rust/compile/issue-4143.rs: New regression test.

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() {}