Check that the preceding line for a line break is non-empty.

src/parser/line_break.rs

@@ -9,6 +9,7 @@ use crate::error::CustomError;
 use crate::error::MyError;
 use crate::error::Res;
 use crate::parser::util::get_consumed;
+use crate::parser::util::get_current_line_before_position;
 use crate::parser::util::get_one_before;
 use crate::parser::LineBreak;
 
@@ -28,7 +29,6 @@ fn pre<'r, 's>(context: Context<'r, 's>, input: &'s str) -> Res<&'s str, ()> {
     let preceding_character = get_one_before(document_root, input)
         .map(|slice| slice.chars().next())
         .flatten();
-    // TODO: Must be at the end of a non-empty line so instead of getting one character before, we need to grab the entire line.
     match preceding_character {
         // If None, we are at the start of the file
         None | Some('\\') => {
@@ -38,5 +38,22 @@ fn pre<'r, 's>(context: Context<'r, 's>, input: &'s str) -> Res<&'s str, ()> {
         }
         _ => {}
     };
+    let current_line = get_current_line_before_position(document_root, input);
+    match current_line {
+        Some(line) => {
+            let is_non_empty_line = line.chars().any(|c| !c.is_whitespace());
+            if !is_non_empty_line {
+                return Err(nom::Err::Error(CustomError::MyError(MyError(
+                    "Not a valid pre line for line break.",
+                ))));
+            }
+        }
+        None => {
+            return Err(nom::Err::Error(CustomError::MyError(MyError(
+                "No preceding line for line break.",
+            ))));
+        }
+    }
+
     Ok((input, ()))
 }

src/parser/util.rs

@@ -59,6 +59,32 @@ pub fn get_one_before<'s>(document: &'s str, current_position: &'s str) -> Optio
     Some(&document[previous_character_offset..offset])
 }
 
+/// Get the line current_position is on up until current_position
+pub fn get_current_line_before_position<'s>(
+    document: &'s str,
+    current_position: &'s str,
+) -> Option<&'s str> {
+    assert!(is_slice_of(document, current_position));
+    if document.as_ptr() as usize == current_position.as_ptr() as usize {
+        return None;
+    }
+    let offset = current_position.as_ptr() as usize - document.as_ptr() as usize;
+    let mut previous_character_offset = offset;
+    loop {
+        let new_offset = document.floor_char_boundary(previous_character_offset - 1);
+        let new_line = &document[new_offset..offset];
+        let leading_char = new_line
+            .chars()
+            .next()
+            .expect("Impossible to not have at least 1 character to read.");
+        if "\r\n".contains(leading_char) || new_offset == 0 {
+            break;
+        }
+        previous_character_offset = new_offset;
+    }
+    Some(&document[previous_character_offset..offset])
+}
+
 /// Check if the child string slice is a slice of the parent string slice.
 fn is_slice_of(parent: &str, child: &str) -> bool {
     let parent_start = parent.as_ptr() as usize;

toy_language.txt

@@ -1,2 +1,3 @@
-before src_foo{ipsum} after
-src_bar[lorem]{ipsum}
+foo bar baz
+
+lorem ipsum