Raise an error if recursion depth exceeds a maximum value

This is preferable to having the assembler crash with a stack overflow
error, because the user can now see which invocation caused the
overflow.

1 files changed, 6 insertions, 0 deletions

diff --git a/src/stages/intermediate.rs b/src/stages/intermediate.rs
index 07773a0..8cabe26 100644
--- a/src/stages/intermediate.rs
+++ b/src/stages/intermediate.rs
@@ -438,6 +438,12 @@ impl IntermediateParser {
                             unreachable!("Uncaught duplicate macro argument name '{name}'");
                         };
                     }
+                    // Test the current recursion depth.
+                    if self.environment_stack.len() == MAX_RECURSION_DEPTH {
+                        let error = IntermediateError::MaxRecursionDepthExceeded;
+                        self.errors.push(Tracked::from(error, source.clone()));
+                        return None;
+                    }
                     // Invoke the macro once.
                     let env = Environment { arguments: argument_map, id: next_id!() };
                     self.environment_stack.push(env);