From 54c66fb4d6eb71b576da7ed9a0af4845e10c36be Mon Sep 17 00:00:00 2001
From: Tom Alexander <tom@fizz.buzz>
Date: Mon, 2 Oct 2023 19:07:12 -0400
Subject: [PATCH] Change get_property to allow absent values.

We're returning an Option<> anyway so might as well handle absent values.
---
 src/compare/util.rs | 17 ++++++++---------
 1 file changed, 8 insertions(+), 9 deletions(-)

diff --git a/src/compare/util.rs b/src/compare/util.rs
index afaedf3..4c2578d 100644
--- a/src/compare/util.rs
+++ b/src/compare/util.rs
@@ -172,9 +172,7 @@ fn maybe_token_to_usize(
 
 /// Get a named property from the emacs token.
 ///
-/// Returns Ok(None) if value is nil.
-///
-/// Returns error if the attribute is not specified on the token at all.
+/// Returns Ok(None) if value is nil or absent.
 pub(crate) fn get_property<'b, 's, 'x>(
     emacs: &'b Token<'s>,
     key: &'x str,
@@ -185,14 +183,15 @@ pub(crate) fn get_property<'b, 's, 'x>(
         .nth(1)
         .ok_or("Should have an attributes child.")?;
     let attributes_map = attributes_child.as_map()?;
-    let prop = attributes_map
-        .get(key)
-        .ok_or(format!("Missing {} attribute.", key))?;
-    match prop.as_atom() {
-        Ok("nil") => return Ok(None),
+    let prop = attributes_map.get(key).map(|token| *token);
+    match prop
+        .map(|token| token.as_atom())
+        .map_or(Ok(None), |r| r.map(Some))?
+    {
+        Some("nil") => return Ok(None),
         _ => {}
     };
-    Ok(Some(*prop))
+    Ok(prop)
 }
 
 /// Get a named property containing an unquoted atom from the emacs token.