macros: add compile_error! macro

addresses Rust-GCC#927

Signed-off-by: Zixing Liu <[email protected]>

gcc/rust/expand/rust-macro-builtins.cc

@@ -236,4 +236,20 @@ MacroBuiltin::include_str (Location invoc_locus, AST::MacroInvocData &invoc)
   return AST::ASTFragment ({node});
 }
 
+/* Expand builtin macro compile_error!("error"), which forces a compile error
+   during the compile time. */
+AST::ASTFragment
+MacroBuiltin::compile_error (Location invoc_locus, AST::MacroInvocData &invoc)
+{
+  auto lit_expr
+    = parse_single_string_literal (invoc.get_delim_tok_tree (), invoc_locus);
+  if (lit_expr == nullptr)
+    return AST::ASTFragment::create_error ();
+
+  std::string error_string = lit_expr->as_string ();
+  rust_error_at (invoc_locus, "%s", error_string.c_str ());
+
+  return AST::ASTFragment::create_error ();
+}
+
 } // namespace Rust

gcc/rust/expand/rust-macro-builtins.h

@@ -77,6 +77,9 @@ class MacroBuiltin
 
   static AST::ASTFragment include_str (Location invoc_locus,
 				       AST::MacroInvocData &invoc);
+
+  static AST::ASTFragment compile_error (Location invoc_locus,
+					 AST::MacroInvocData &invoc);
 };
 } // namespace Rust
 

gcc/rust/util/rust-hir-map.cc

@@ -753,6 +753,7 @@ Mappings::insert_macro_def (AST::MacroRulesDefinition *macro)
       {"column", MacroBuiltin::column},
       {"include_bytes", MacroBuiltin::include_bytes},
       {"include_str", MacroBuiltin::include_str},
+      {"compile_error", MacroBuiltin::compile_error},
     };
 
   auto builtin = builtin_macros.find (macro->get_rule_name ());

gcc/testsuite/rust/compile/builtin_macro_compile_error.rs

@@ -0,0 +1,12 @@
+macro_rules! compile_error {
+  () => {{}};
+}
+
+fn main () {
+  let message = "error message";
+  compile_error! (message); // { dg-error "argument must be a string literal" "" }
+  compile_error! (); // { dg-error "macro takes 1 argument" "" }
+  compile_error! ("a", "b"); // { dg-error "macro takes 1 argument" "" }
+  compile_error! ("expected error message"); // { dg-error "expected error message" }
+  compile_error! ("expected error message",); // { dg-error "expected error message" }
+}