session: Add basic prelude injection

gcc/rust/Make-lang.in

@@ -247,6 +247,7 @@ GRS_OBJS = \
 	rust/rust-desugar-question-mark.o \
 	rust/rust-desugar-apit.o \
 	rust/rust-desugar-try-block.o \
+	rust/rust-std-prelude.o \
     $(END)
 # removed object files from here
 

gcc/rust/resolve/rust-std-prelude.cc

@@ -0,0 +1,61 @@
+// Copyright (C) 2025 Free Software Foundation, Inc.
+
+// This file is part of GCC.
+
+// GCC is free software; you can redistribute it and/or modify it under
+// the terms of the GNU General Public License as published by the Free
+// Software Foundation; either version 3, or (at your option) any later
+// version.
+
+// GCC is distributed in the hope that it will be useful, but WITHOUT ANY
+// WARRANTY; without even the implied warranty of MERCHANTABILITY or
+// FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+// for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with GCC; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+#include "rust-std-prelude.h"
+#include "input.h"
+#include "rust-ast-builder.h"
+#include "rust-ast.h"
+#include "rust-item.h"
+
+namespace Rust {
+namespace AST {
+
+void
+StdPrelude::inject (AST::Crate &crate)
+{
+  // The actual logic is quite complicated, as this depends on editions and on
+  // whether or not we're compiling in #[no_std] mode or not. For now, we just
+  // want core's prelude, so that's what we'll inject
+
+  auto loc = UNKNOWN_LOCATION;
+
+  auto prelude_import
+    = Attribute (SimplePath::from_str ("prelude_import", loc), nullptr);
+  std::vector<Attribute> attributes = {prelude_import};
+
+  // core::prelude::rust_2018::*
+  auto core = SimplePathSegment ("core", loc);
+  auto prelude = SimplePathSegment ("prelude", loc);
+  auto rust_2018 = SimplePathSegment ("rust_2018", loc);
+
+  auto path = SimplePath ({core, prelude, rust_2018});
+
+  auto use
+    = std::make_unique<UseTreeGlob> (UseTreeGlob::PathType::PATH_PREFIXED, path,
+				     loc);
+
+  auto final_import
+    = std::make_unique<UseDeclaration> (std::move (use),
+					Visibility::create_private (),
+					std::move (attributes), loc);
+
+  crate.items.insert (crate.items.begin (), std::move (final_import));
+}
+
+} // namespace AST
+} // namespace Rust

gcc/rust/resolve/rust-std-prelude.h

@@ -0,0 +1,39 @@
+// Copyright (C) 2025 Free Software Foundation, Inc.
+
+// This file is part of GCC.
+
+// GCC is free software; you can redistribute it and/or modify it under
+// the terms of the GNU General Public License as published by the Free
+// Software Foundation; either version 3, or (at your option) any later
+// version.
+
+// GCC is distributed in the hope that it will be useful, but WITHOUT ANY
+// WARRANTY; without even the implied warranty of MERCHANTABILITY or
+// FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+// for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with GCC; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+#ifndef RUST_PRELUDE_INJECT_H
+#define RUST_PRELUDE_INJECT_H
+
+#include "rust-ast.h"
+
+namespace Rust {
+namespace AST {
+
+class StdPrelude
+{
+public:
+  /**
+   * Inject the standard library prelude into a given crate
+   */
+  static void inject (AST::Crate &crate);
+};
+
+} // namespace AST
+} // namespace Rust
+
+#endif // ! RUST_PRELUDE_INJECT_H

gcc/rust/rust-session-manager.cc

@@ -21,6 +21,7 @@
 #include "rust-desugar-for-loops.h"
 #include "rust-desugar-question-mark.h"
 #include "rust-desugar-apit.h"
+#include "rust-std-prelude.h"
 #include "rust-diagnostics.h"
 #include "rust-expression-yeast.h"
 #include "rust-hir-pattern-analysis.h"
@@ -974,6 +975,8 @@ Session::expansion (AST::Crate &crate, Resolver2_0::NameResolutionContext &ctx)
 {
   rust_debug ("started expansion");
 
+  // AST::StdPrelude::inject (crate);
+
   /* rustc has a modification to windows PATH temporarily here, which may end
    * up being required */