From 7fafbfb6bbce54c3b397167b04f9698cef87e26f Mon Sep 17 00:00:00 2001
From: Tom Alexander <tom@fizz.buzz>
Date: Wed, 16 Aug 2023 17:37:19 -0400
Subject: [PATCH] Do not consume whitespace in the final plain list item.

---
 src/parser/plain_list.rs | 41 ++++++++++++++++++++++++++++++++--------
 1 file changed, 33 insertions(+), 8 deletions(-)

diff --git a/src/parser/plain_list.rs b/src/parser/plain_list.rs
index 73110481..4d6e5cfb 100644
--- a/src/parser/plain_list.rs
+++ b/src/parser/plain_list.rs
@@ -42,18 +42,27 @@ pub fn plain_list<'r, 's>(context: Context<'r, 's>, input: &'s str) -> Res<&'s s
             class: ExitClass::Beta,
             exit_matcher: &plain_list_end,
         }));
+    // children stores tuple of (input string, parsed object) so we can re-parse the final item
     let mut children = Vec::new();
     let mut first_item_indentation: Option<usize> = None;
     let mut remaining = input;
 
+    // The final list item does not consume trailing blank lines (which instead get consumed by the list). We have three options here:
+    //
+    // 1. Parse all items while consuming trailing whitespace, then edit the final item to remove trailing whitespace.
+    // 2. Parse all items without consuming trailing whitespace, then edit all but the final one to add in the trailing whitespace.
+    // 3. Re-parse the final item with consume trailing whitespace disabled.
+    //
+    // While #3 is the most slow, it also seems to cleanest and involves the least manual mutation of already-parsed objects so I am going with #3 for now, but we should revisit #1 or #2 when the parser is more developed.
+
     loop {
         let list_item = parser_with_context!(plain_list_item)(&parser_context)(remaining);
         match list_item {
             Ok((remain, item))
                 if item.indentation == *first_item_indentation.get_or_insert(item.indentation) =>
             {
+                children.push((remaining, item));
                 remaining = remain;
-                children.push(item);
             }
             Ok(_) | Err(_) => {
                 break;
@@ -66,16 +75,31 @@ pub fn plain_list<'r, 's>(context: Context<'r, 's>, input: &'s str) -> Res<&'s s
         }
     }
 
-    if children.is_empty() {
-        return Err(nom::Err::Error(CustomError::MyError(MyError(
-            "Plain lists require at least one element.",
-        ))));
-    }
+    let (final_child_start, _final_item_first_parse) = match children.pop() {
+        Some(final_child) => final_child,
+        None => {
+            return Err(nom::Err::Error(CustomError::MyError(MyError(
+                "Plain lists require at least one element.",
+            ))));
+        }
+    };
+    let final_item_context =
+        parser_context.with_additional_node(ContextElement::ConsumeTrailingWhitespace(false));
+    let (remaining, reparsed_final_item) =
+        parser_with_context!(plain_list_item)(&final_item_context)(final_child_start)?;
+    children.push((final_child_start, reparsed_final_item));
 
-    // TODO: trailing whitespace
+    let (remaining, _trailing_ws) =
+        maybe_consume_trailing_whitespace_if_not_exiting(context, remaining)?;
 
     let source = get_consumed(input, remaining);
-    Ok((remaining, PlainList { source, children }))
+    Ok((
+        remaining,
+        PlainList {
+            source,
+            children: children.into_iter().map(|(_start, item)| item).collect(),
+        },
+    ))
 }
 
 #[cfg_attr(feature = "tracing", tracing::instrument(ret, level = "debug"))]
@@ -109,6 +133,7 @@ pub fn plain_list_item<'r, 's>(
 
     let (remaining, _ws) = space1(remaining)?;
     let parser_context = context
+        .with_additional_node(ContextElement::ConsumeTrailingWhitespace(true))
         .with_additional_node(ContextElement::ListItem(indent_level))
         .with_additional_node(ContextElement::ExitMatcherNode(ExitMatcherNode {
             class: ExitClass::Beta,