Add option_env! support

gcc/rust/ChangeLog:
	* expand/rust-macro-builtins-utility.cc: Add macro expansion for
	option_env with eager expansion
	* expand/rust-macro-builtins.cc: Add option_env to builtin list
	* expand/rust-macro-builtins.h: Add option_env handler to header
	file
	* resolve/rust-late-name-resolver-2.0.cc: Prevent NR2.0 from
	recursing into lang-item segments

gcc/testsuite/ChangeLog:
	* rust/compile/macros/builtin/option_env1.rs: Add success case for option_env
	* rust/compile/macros/builtin/option_env2.rs: Add failure case for option_env
	* rust/execute/torture/builtin_macro_option_env.rs: Add
	execution case for option_env

4 files changed, 85 insertions, 1 deletions

diff --git a/gcc/rust/expand/rust-macro-builtins-utility.cc b/gcc/rust/expand/rust-macro-builtins-utility.cc
index ff64879..28829a1 100644
--- a/gcc/rust/expand/rust-macro-builtins-utility.cc
+++ b/gcc/rust/expand/rust-macro-builtins-utility.cc
@@ -17,6 +17,7 @@
 // <http://www.gnu.org/licenses/>.
 
 #include "rust-fmt.h"
+#include "rust-ast-builder.h"
 #include "rust-macro-builtins.h"
 #include "rust-macro-builtins-helpers.h"
 
@@ -226,6 +227,83 @@ MacroBuiltin::env_handler (location_t invoc_locus, AST::MacroInvocData &invoc,
   return AST::Fragment ({node}, std::move (tok));
 }
 
+/* Expand builtin macro option_env!(), which inspects an environment variable at
+   compile time. */
+tl::optional<AST::Fragment>
+MacroBuiltin::option_env_handler (location_t invoc_locus,
+				  AST::MacroInvocData &invoc,
+				  AST::InvocKind semicolon)
+{
+  auto invoc_token_tree = invoc.get_delim_tok_tree ();
+  MacroInvocLexer lex (invoc_token_tree.to_token_stream ());
+  Parser<MacroInvocLexer> parser (lex);
+
+  auto last_token_id = macro_end_token (invoc_token_tree, parser);
+  std::unique_ptr<AST::LiteralExpr> lit_expr = nullptr;
+  bool has_error = false;
+
+  auto start = lex.get_offs ();
+  auto expanded_expr = try_expand_many_expr (parser, last_token_id,
+					     invoc.get_expander (), has_error);
+  auto end = lex.get_offs ();
+
+  auto tokens = lex.get_token_slice (start, end);
+
+  if (has_error)
+    return AST::Fragment::create_error ();
+
+  auto pending = check_for_eager_invocations (expanded_expr);
+  if (!pending.empty ())
+    return make_eager_builtin_invocation (BuiltinMacro::OptionEnv, invoc_locus,
+					  invoc_token_tree,
+					  std::move (pending));
+
+  if (expanded_expr.size () != 1)
+    {
+      rust_error_at (invoc_locus, "%<option_env!%> takes 1 argument");
+      return AST::Fragment::create_error ();
+    }
+
+  if (expanded_expr.size () > 0)
+    if (!(lit_expr
+	  = try_extract_string_literal_from_fragment (invoc_locus,
+						      expanded_expr[0])))
+      return AST::Fragment::create_error ();
+
+  parser.skip_token (last_token_id);
+
+  auto env_value = getenv (lit_expr->as_string ().c_str ());
+  AST::Builder b (invoc_locus);
+
+  if (env_value == nullptr)
+    {
+      auto none_expr = std::unique_ptr<AST::Expr> (
+	new AST::PathInExpression (LangItem::Kind::OPTION_NONE, {},
+				   invoc_locus));
+
+      auto node = AST::SingleASTNode (std::move (none_expr));
+      std::vector<AST::SingleASTNode> nodes;
+      nodes.push_back (node);
+
+      return AST::Fragment (nodes, std::vector<std::unique_ptr<AST::Token>> ());
+    }
+  std::vector<std::unique_ptr<AST::Expr>> args;
+  args.push_back (b.literal_string (env_value));
+
+  std::unique_ptr<AST::Expr> some_expr
+    = b.call (std::unique_ptr<AST::Expr> (
+		new AST::PathInExpression (LangItem::Kind::OPTION_SOME, {},
+					   invoc_locus)),
+	      std::move (args));
+
+  auto node = AST::SingleASTNode (std::move (some_expr));
+
+  std::vector<AST::SingleASTNode> nodes;
+  nodes.push_back (node);
+
+  return AST::Fragment (nodes, std::vector<std::unique_ptr<AST::Token>> ());
+}
+
 tl::optional<AST::Fragment>
 MacroBuiltin::cfg_handler (location_t invoc_locus, AST::MacroInvocData &invoc,
 			   AST::InvocKind semicolon)
diff --git a/gcc/rust/expand/rust-macro-builtins.cc b/gcc/rust/expand/rust-macro-builtins.cc
index 07a1f3c..59b8f6a 100644
--- a/gcc/rust/expand/rust-macro-builtins.cc
+++ b/gcc/rust/expand/rust-macro-builtins.cc
@@ -120,8 +120,8 @@ std::unordered_map<std::string, AST::MacroTranscriberFunc>
     {"format_args_nl", format_args_maker (AST::FormatArgs::Newline::Yes)},
     {"asm", inline_asm_maker (AST::AsmKind::Inline)},
     {"global_asm", inline_asm_maker (AST::AsmKind::Global)},
+    {"option_env", MacroBuiltin::option_env_handler},
     /* Unimplemented macro builtins */
-    {"option_env", MacroBuiltin::sorry},
     {"concat_idents", MacroBuiltin::sorry},
     {"module_path", MacroBuiltin::sorry},
     {"log_syntax", MacroBuiltin::sorry},
diff --git a/gcc/rust/expand/rust-macro-builtins.h b/gcc/rust/expand/rust-macro-builtins.h
index b0c4a64..1d17b43 100644
--- a/gcc/rust/expand/rust-macro-builtins.h
+++ b/gcc/rust/expand/rust-macro-builtins.h
@@ -159,6 +159,10 @@ public:
 						  AST::MacroInvocData &invoc,
 						  AST::InvocKind semicolon);
 
+  static tl::optional<AST::Fragment>
+  option_env_handler (location_t invoc_locus, AST::MacroInvocData &invoc,
+		      AST::InvocKind semicolon);
+
   static tl::optional<AST::Fragment> cfg_handler (location_t invoc_locus,
 						  AST::MacroInvocData &invoc,
 						  AST::InvocKind semicolon);
diff --git a/gcc/rust/resolve/rust-late-name-resolver-2.0.cc b/gcc/rust/resolve/rust-late-name-resolver-2.0.cc
index b0364d1..ec20e9a 100644
--- a/gcc/rust/resolve/rust-late-name-resolver-2.0.cc
+++ b/gcc/rust/resolve/rust-late-name-resolver-2.0.cc
@@ -254,6 +254,8 @@ Late::visit (AST::PathInExpression &expr)
   // TODO: How do we have a nice error with `can't capture dynamic environment
   // in a function item` error here?
   // do we emit it in `get<Namespace::Labels>`?
+  if (expr.is_lang_item ())
+    return;
 
   auto resolved
     = ctx.values.resolve_path (expr.get_segments ()).or_else ([&] () {