Adjust line number clearance (#5093)

Co-authored-by: Laurenz <laurmaedje@gmail.com>

3 files changed, 64 insertions, 21 deletions

diff --git a/crates/typst/src/layout/flow/compose.rs b/crates/typst/src/layout/flow/compose.rs
index 003e4e72..6f14618e 100644
--- a/crates/typst/src/layout/flow/compose.rs
+++ b/crates/typst/src/layout/flow/compose.rs
@@ -1,6 +1,8 @@
 use std::num::NonZeroUsize;
 
-use super::{distribute, Config, FlowResult, PlacedChild, Skip, Stop, Work};
+use super::{
+    distribute, Config, FlowResult, LineNumberConfig, PlacedChild, Skip, Stop, Work,
+};
 use crate::diag::SourceResult;
 use crate::engine::Engine;
 use crate::foundations::{Content, NativeElement, Packed, Resolve, Smart};
@@ -13,7 +15,7 @@ use crate::layout::{
     OuterHAlignment, PlacementScope, Point, Region, Regions, Rel, Size,
 };
 use crate::model::{
-    FootnoteElem, FootnoteEntry, LineNumberingScope, Numbering, ParLine, ParLineMarker,
+    FootnoteElem, FootnoteEntry, LineNumberingScope, Numbering, ParLineMarker,
 };
 use crate::syntax::Span;
 use crate::utils::NonZeroExt;
@@ -198,10 +200,11 @@ impl<'a, 'b> Composer<'a, 'b, '_, '_> {
         let mut output = insertions.finalize(self.work, self.config, inner);
 
         // Lay out per-column line numbers.
-        if self.config.root {
+        if let Some(line_config) = &self.config.line_numbers {
             layout_line_numbers(
                 self.engine,
                 self.config,
+                line_config,
                 locator,
                 self.column,
                 &mut output,
@@ -647,6 +650,7 @@ impl<'a, 'b> Insertions<'a, 'b> {
 fn layout_line_numbers(
     engine: &mut Engine,
     config: &Config,
+    line_config: &LineNumberConfig,
     locator: Locator,
     column: usize,
     output: &mut Frame,
@@ -654,9 +658,7 @@ fn layout_line_numbers(
     let mut locator = locator.split();
 
     // Reset page-scoped line numbers if currently at the first column.
-    if column == 0
-        && ParLine::numbering_scope_in(config.shared) == LineNumberingScope::Page
-    {
+    if column == 0 && line_config.scope == LineNumberingScope::Page {
         let reset = layout_line_number_reset(engine, config, &mut locator)?;
         output.push_frame(Point::zero(), reset);
     }
@@ -711,9 +713,11 @@ fn layout_line_numbers(
                 .resolve(config.shared)
         };
 
-        // Compute the marker's horizontal position. Will be adjusted based on
-        // the maximum number width later.
-        let clearance = marker.number_clearance.resolve(config.shared);
+        // Determine how much space to leave between the column and the number.
+        let clearance = match marker.number_clearance {
+            Smart::Auto => line_config.default_clearance,
+            Smart::Custom(rel) => rel.resolve(config.shared),
+        };
 
         // Compute the base X position.
         let x = match margin {
diff --git a/crates/typst/src/layout/flow/mod.rs b/crates/typst/src/layout/flow/mod.rs
index 8a10b05d..5db70ecb 100644
--- a/crates/typst/src/layout/flow/mod.rs
+++ b/crates/typst/src/layout/flow/mod.rs
@@ -19,14 +19,14 @@ use self::compose::{compose, Composer};
 use self::distribute::distribute;
 use crate::diag::{bail, At, SourceDiagnostic, SourceResult};
 use crate::engine::{Engine, Route, Sink, Traced};
-use crate::foundations::{Content, Packed, StyleChain};
+use crate::foundations::{Content, Packed, Resolve, StyleChain};
 use crate::introspection::{
     Introspector, Location, Locator, LocatorLink, SplitLocator, Tag,
 };
 use crate::layout::{
-    Abs, Dir, Fragment, Frame, PlacementScope, Region, Regions, Rel, Size,
+    Abs, Dir, Em, Fragment, Frame, PageElem, PlacementScope, Region, Regions, Rel, Size,
 };
-use crate::model::{FootnoteElem, FootnoteEntry};
+use crate::model::{FootnoteElem, FootnoteEntry, LineNumberingScope, ParLine};
 use crate::realize::{realize, Arenas, Pair, RealizationKind};
 use crate::text::TextElem;
 use crate::utils::{NonZeroExt, Numeric};
@@ -187,6 +187,18 @@ pub(crate) fn layout_flow(
             gap: FootnoteEntry::gap_in(shared),
             expand: regions.expand.x,
         },
+        line_numbers: root.then(|| LineNumberConfig {
+            scope: ParLine::numbering_scope_in(shared),
+            default_clearance: {
+                let width = if PageElem::flipped_in(shared) {
+                    PageElem::height_in(shared)
+                } else {
+                    PageElem::width_in(shared)
+                };
+                (0.026 * width.unwrap_or_default())
+                    .clamp(Em::new(0.75).resolve(shared), Em::new(2.5).resolve(shared))
+            },
+        }),
     };
 
     // Collect the elements into pre-processed children. These are much easier
@@ -311,6 +323,8 @@ struct Config<'x> {
     columns: ColumnConfig,
     /// Settings for footnotes.
     footnote: FootnoteConfig,
+    /// Settings for line numbers.
+    line_numbers: Option<LineNumberConfig>,
 }
 
 /// Configuration of footnotes.
@@ -338,6 +352,14 @@ struct ColumnConfig {
     dir: Dir,
 }
 
+/// Configuration of line numbers.
+struct LineNumberConfig {
+    /// Where line numbers are reset.
+    scope: LineNumberingScope,
+    /// The default clearance for `auto`.
+    default_clearance: Abs,
+}
+
 /// The result type for flow layout.
 ///
 /// The `Err(_)` variant incorporate control flow events for finishing and
diff --git a/crates/typst/src/model/par.rs b/crates/typst/src/model/par.rs
index 2e23bd74..b50fca8b 100644
--- a/crates/typst/src/model/par.rs
+++ b/crates/typst/src/model/par.rs
@@ -7,7 +7,7 @@ use crate::foundations::{
     StyleVec, Unlabellable,
 };
 use crate::introspection::{Count, CounterUpdate, Locatable};
-use crate::layout::{Abs, Em, HAlignment, Length, OuterHAlignment};
+use crate::layout::{Em, HAlignment, Length, OuterHAlignment};
 use crate::model::Numbering;
 use crate::utils::singleton;
 
@@ -219,17 +219,27 @@ impl Unlabellable for Packed<ParbreakElem> {}
 ///
 /// This element is exclusively used for line number configuration and cannot
 /// be placed.
-#[elem(name = "line", title = "Paragraph Line", Construct, Locatable)]
+///
+/// ```example
+/// >>> #set page(margin: (left: 3em))
+/// #set par.line(numbering: "1")
+///
+/// Roses are red. \
+/// Violets are blue. \
+/// Typst is there for you.
+/// ```
+#[elem(name = "line", title = "Paragraph Line", keywords = ["line numbering"], Construct, Locatable)]
 pub struct ParLine {
     /// How to number each line. Accepts a
     /// [numbering pattern or function]($numbering).
     ///
     /// ```example
-    /// #set par.line(numbering: "1")
+    /// >>> #set page(margin: (left: 3em))
+    /// #set par.line(numbering: "I")
     ///
     /// Roses are red. \
     /// Violets are blue. \
-    /// Typst is awesome.
+    /// Typst is there for you.
     /// ```
     #[ghost]
     pub numbering: Option<Numbering>,
@@ -241,6 +251,7 @@ pub struct ParLine {
     /// the current text direction.
     ///
     /// ```example
+    /// >>> #set page(margin: (left: 3em))
     /// #set par.line(numbering: "I", number-align: left)
     ///
     /// Hello world! \
@@ -253,6 +264,7 @@ pub struct ParLine {
     /// The margin at which line numbers appear.
     ///
     /// ```example
+    /// >>> #set page(margin: (right: 3em))
     /// #set par.line(numbering: "1", number-margin: right)
     ///
     /// = Report
@@ -265,10 +277,14 @@ pub struct ParLine {
 
     /// The distance between line numbers and text.
     ///
+    /// The default value of `{auto}` results in a clearance that is adaptive to
+    /// the page width and yields reasonable results in most cases.
+    ///
     /// ```example
+    /// >>> #set page(margin: (left: 3em))
     /// #set par.line(
     ///   numbering: "1",
-    ///   number-clearance: 0.5pt
+    ///   number-clearance: 4pt
     /// )
     ///
     /// Typesetting \
@@ -276,8 +292,8 @@ pub struct ParLine {
     /// Layout
     /// ```
     #[ghost]
-    #[default(Length::from(Abs::cm(1.0)))]
-    pub number_clearance: Length,
+    #[default]
+    pub number_clearance: Smart<Length>,
 
     /// Controls when to reset line numbering.
     ///
@@ -285,8 +301,9 @@ pub struct ParLine {
     /// is never reset, or `"page"`, indicating it is reset on every page.
     ///
     /// ```example
+    /// >>> #set page(margin: (left: 3em))
     /// #set par.line(
-    ///   numbering: "1.",
+    ///   numbering: "1",
     ///   numbering-scope: "page"
     /// )
     ///
@@ -339,7 +356,7 @@ pub struct ParLineMarker {
 
     #[internal]
     #[required]
-    pub number_clearance: Length,
+    pub number_clearance: Smart<Length>,
 }
 
 impl Construct for ParLineMarker {