Introduce the tab_width setting and give tabs a greater value when counting indentation level.

src/context/global_settings.rs

@@ -2,6 +2,7 @@ use std::collections::BTreeSet;
 
 use super::FileAccessInterface;
 use super::LocalFileAccessInterface;
+use crate::types::IndentationLevel;
 use crate::types::Object;
 
 // TODO: Ultimately, I think we'll need most of this: https://orgmode.org/manual/In_002dbuffer-Settings.html
@@ -16,6 +17,11 @@ pub struct GlobalSettings<'g, 's> {
     ///
     /// Corresponds to the org-list-allow-alphabetical elisp variable.
     pub org_list_allow_alphabetical: bool,
+
+    /// How many spaces a tab should be equal to.
+    ///
+    /// Corresponds to the tab-width elisp variable.
+    pub tab_width: IndentationLevel,
 }
 
 impl<'g, 's> GlobalSettings<'g, 's> {
@@ -28,6 +34,7 @@ impl<'g, 's> GlobalSettings<'g, 's> {
             in_progress_todo_keywords: BTreeSet::new(),
             complete_todo_keywords: BTreeSet::new(),
             org_list_allow_alphabetical: false,
+            tab_width: 8,
         }
     }
 }

src/parser/plain_list.rs

@@ -22,6 +22,7 @@ use super::element_parser::element;
 use super::object_parser::standard_set_object;
 use super::org_source::OrgSource;
 use super::util::include_input;
+use super::util::indentation_level;
 use super::util::non_whitespace_character;
 use crate::context::parser_with_context;
 use crate::context::ContextElement;
@@ -39,6 +40,7 @@ use crate::parser::util::maybe_consume_trailing_whitespace_if_not_exiting;
 use crate::parser::util::org_space;
 use crate::parser::util::start_of_line;
 use crate::types::CheckboxType;
+use crate::types::IndentationLevel;
 use crate::types::Object;
 use crate::types::PlainList;
 use crate::types::PlainListItem;
@@ -87,7 +89,7 @@ pub(crate) fn plain_list<'b, 'g, 'r, 's>(
     let parser_context = parser_context.with_additional_node(&contexts[2]);
     // 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 first_item_indentation: Option<IndentationLevel> = 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:
@@ -148,9 +150,7 @@ fn plain_list_item<'b, 'g, 'r, 's>(
     input: OrgSource<'s>,
 ) -> Res<OrgSource<'s>, PlainListItem<'s>> {
     start_of_line(input)?;
-    let (remaining, leading_whitespace) = space0(input)?;
-    // It is fine that we get the indent level using the number of bytes rather than the number of characters because nom's space0 only matches space and tab (0x20 and 0x09)
-    let indent_level = leading_whitespace.len();
+    let (remaining, (indent_level, _leading_whitespace)) = indentation_level(context, input)?;
     let (remaining, bull) = verify(
         parser_with_context!(bullet)(context),
         |bull: &OrgSource<'_>| Into::<&str>::into(bull) != "*" || indent_level > 0,
@@ -287,7 +287,7 @@ fn plain_list_end<'b, 'g, 'r, 's>(
     )))(input)
 }
 
-const fn plain_list_item_end(indent_level: usize) -> impl ContextMatcher {
+const fn plain_list_item_end(indent_level: IndentationLevel) -> impl ContextMatcher {
     let line_indented_lte_matcher = line_indented_lte(indent_level);
     move |context, input: OrgSource<'_>| {
         _plain_list_item_end(context, input, &line_indented_lte_matcher)
@@ -310,20 +310,23 @@ fn _plain_list_item_end<'b, 'g, 'r, 's>(
     )))(input)
 }
 
-const fn line_indented_lte(indent_level: usize) -> impl ContextMatcher {
+const fn line_indented_lte(indent_level: IndentationLevel) -> impl ContextMatcher {
     move |context, input: OrgSource<'_>| _line_indented_lte(context, input, indent_level)
 }
 
 #[cfg_attr(feature = "tracing", tracing::instrument(ret, level = "debug"))]
 fn _line_indented_lte<'b, 'g, 'r, 's>(
-    _context: RefContext<'b, 'g, 'r, 's>,
+    context: RefContext<'b, 'g, 'r, 's>,
     input: OrgSource<'s>,
-    indent_level: usize,
+    indent_level: IndentationLevel,
 ) -> Res<OrgSource<'s>, OrgSource<'s>> {
     let matched = recognize(verify(
-        tuple((space0::<OrgSource<'_>, _>, non_whitespace_character)),
+        tuple((
+            parser_with_context!(indentation_level)(context),
+            non_whitespace_character,
+        )),
         // It is fine that we get the indent level using the number of bytes rather than the number of characters because nom's space0 only matches space and tab (0x20 and 0x09)
-        |(_space0, _anychar)| _space0.len() <= indent_level,
+        |((indentation_level, _leading_whitespace), _anychar)| *indentation_level <= indent_level,
     ))(input)?;
 
     Ok(matched)

src/parser/util.rs

@@ -20,6 +20,7 @@ use crate::context::RefContext;
 use crate::error::CustomError;
 use crate::error::MyError;
 use crate::error::Res;
+use crate::types::IndentationLevel;
 
 pub(crate) const WORD_CONSTITUENT_CHARACTERS: &str =
     "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
@@ -240,7 +241,7 @@ pub(crate) fn org_space<'s>(input: OrgSource<'s>) -> Res<OrgSource<'s>, char> {
 pub(crate) fn org_space_or_line_ending<'s>(
     input: OrgSource<'s>,
 ) -> Res<OrgSource<'s>, OrgSource<'s>> {
-    alt((recognize(one_of(" \t")), org_line_ending))(input)
+    alt((recognize(org_space), org_line_ending))(input)
 }
 
 /// Match a line break or the end of the file.
@@ -249,3 +250,20 @@ pub(crate) fn org_space_or_line_ending<'s>(
 pub(crate) fn org_line_ending<'s>(input: OrgSource<'s>) -> Res<OrgSource<'s>, OrgSource<'s>> {
     alt((line_ending, eof))(input)
 }
+
+/// Match the whitespace at the beginning of a line and give it an indentation level.
+pub(crate) fn indentation_level<'b, 'g, 'r, 's>(
+    context: RefContext<'b, 'g, 'r, 's>,
+    input: OrgSource<'s>,
+) -> Res<OrgSource<'s>, (IndentationLevel, OrgSource<'s>)> {
+    let (remaining, leading_whitespace) = space0(input)?;
+    let indentation_level = Into::<&str>::into(leading_whitespace)
+        .chars()
+        .map(|c| match c {
+            ' ' => 1,
+            '\t' => context.get_global_settings().tab_width,
+            _ => unreachable!(),
+        })
+        .sum();
+    Ok((remaining, (indentation_level, leading_whitespace)))
+}

src/types/greater_element.rs

@@ -10,10 +10,13 @@ pub struct PlainList<'s> {
     pub children: Vec<PlainListItem<'s>>,
 }
 
+/// The width that something is indented. For example, a single tab character could be a value of 4 or 8.
+pub type IndentationLevel = u16;
+
 #[derive(Debug)]
 pub struct PlainListItem<'s> {
     pub source: &'s str,
-    pub indentation: usize,
+    pub indentation: IndentationLevel,
     pub bullet: &'s str,
     pub checkbox: Option<(CheckboxType, &'s str)>,
     pub tag: Vec<Object<'s>>,

src/types/mod.rs

@@ -16,6 +16,7 @@ pub use greater_element::Drawer;
 pub use greater_element::DynamicBlock;
 pub use greater_element::FootnoteDefinition;
 pub use greater_element::GreaterBlock;
+pub use greater_element::IndentationLevel;
 pub use greater_element::NodeProperty;
 pub use greater_element::PlainList;
 pub use greater_element::PlainListItem;