First-line indents

Co-Authored-By: Martin Haug <mhaug@live.de>

src/eval/collapse.rs

@@ -67,6 +67,11 @@ impl<'a, T: Merge> CollapsingBuilder<'a, T> {
         self.staged.push((item, styles, None));
     }
 
+    /// Iterate over the contained items.
+    pub fn items(&self) -> impl DoubleEndedIterator<Item = &T> {
+        self.builder.items().chain(self.staged.iter().map(|(item, ..)| item))
+    }
+
     /// Return the finish style vec and the common prefix chain.
     pub fn finish(mut self) -> (StyleVec<T>, StyleChain<'a>) {
         self.flush(false);

src/eval/styles.rs

@@ -547,6 +547,17 @@ impl<T> StyleVec<T> {
             .flat_map(|(map, count)| std::iter::repeat(map).take(*count));
         self.items().zip(styles)
     }
+
+    /// Insert an element in the front. The element will share the style of the
+    /// current first element.
+    ///
+    /// This method has no effect if the vector is empty.
+    pub fn push_front(&mut self, item: T) {
+        if !self.maps.is_empty() {
+            self.items.insert(0, item);
+            self.maps[0].1 += 1;
+        }
+    }
 }
 
 impl<T> Default for StyleVec<T> {
@@ -601,6 +612,11 @@ impl<'a, T> StyleVecBuilder<'a, T> {
         Some((item, chain))
     }
 
+    /// Iterate over the contained items.
+    pub fn items(&self) -> std::slice::Iter<'_, T> {
+        self.items.iter()
+    }
+
     /// Finish building, returning a pair of two things:
     /// - a style vector of items with the non-shared styles
     /// - a shared prefix chain of styles that apply to all items

src/eval/template.rs

@@ -445,8 +445,36 @@ impl<'a> Builder<'a> {
 
     /// Finish the currently built paragraph.
     fn finish_par(&mut self, styles: StyleChain<'a>) {
-        let (par, shared) = std::mem::take(&mut self.par).finish();
+        let (mut par, shared) = std::mem::take(&mut self.par).finish();
         if !par.is_empty() {
+            // Paragraph indent should only apply if the paragraph starts with
+            // text and follows directly after another paragraph.
+            let indent = shared.get(ParNode::INDENT);
+            if !indent.is_zero()
+                && par
+                    .items()
+                    .find_map(|child| match child {
+                        ParChild::Spacing(_) => None,
+                        ParChild::Text(_) => Some(true),
+                        ParChild::Node(_) => Some(false),
+                    })
+                    .unwrap_or_default()
+                && self
+                    .flow
+                    .items()
+                    .rev()
+                    .find_map(|child| match child {
+                        FlowChild::Leading => None,
+                        FlowChild::Parbreak => None,
+                        FlowChild::Node(node) => Some(node.is::<ParNode>()),
+                        FlowChild::Spacing(_) => Some(false),
+                        FlowChild::Colbreak => Some(false),
+                    })
+                    .unwrap_or_default()
+            {
+                par.push_front(ParChild::Spacing(SpacingKind::Linear(indent)))
+            }
+
             let node = ParNode(par).pack();
             self.flow.supportive(FlowChild::Node(node), shared);
         }

src/library/par.rs

@@ -36,6 +36,8 @@ impl ParNode {
     pub const LEADING: Linear = Relative::new(0.65).into();
     /// The extra spacing between paragraphs (dependent on scaled font size).
     pub const SPACING: Linear = Relative::new(0.55).into();
+    /// The indent the first line of a consecutive paragraph should have.
+    pub const INDENT: Linear = Linear::zero();
 
     fn construct(_: &mut Context, args: &mut Args) -> TypResult<Template> {
         // The paragraph constructor is special: It doesn't create a paragraph
@@ -75,6 +77,7 @@ impl ParNode {
         styles.set_opt(Self::ALIGN, align);
         styles.set_opt(Self::LEADING, args.named("leading")?);
         styles.set_opt(Self::SPACING, args.named("spacing")?);
+        styles.set_opt(Self::INDENT, args.named("indent")?);
 
         Ok(())
     }

tests/typ/text/indent.typ

@@ -0,0 +1,28 @@
+// Test paragraph indent.
+
+---
+#set par(indent: 12pt, leading: 5pt, spacing: 0pt)
+#set heading(size: 10pt, above: 8pt)
+
+The first paragraph has no indent.
+
+But the second one does.
+
+#image("../../res/tiger.jpg", height: 6pt)
+starts a paragraph without indent.
+
+#align(center, image("../../res/rhino.png", width: 1cm))
+
+= Headings
+- And lists.
+- Have no indent.
+
+  Except if you have another paragraph in them.
+
+#set text(8pt, "Noto Sans Arabic")
+#set par(lang: "ar", leading: 8pt)
+
+= Arabic
+دع النص يمطر عليك
+
+ثم يصبح النص رطبًا وقابل للطرق ويبدو المستند رائعًا.