From aa62d054532e91f988c39dee97c00ce54f18b605 Mon Sep 17 00:00:00 2001
From: Laurenz <laurmaedje@gmail.com>
Date: Sat, 28 Oct 2023 20:05:32 +0200
Subject: [PATCH] Fix justification with hanging indent and negative spacing

Fixes #2419
---
 crates/typst-library/src/layout/par.rs    |  12 +++++++++---
 tests/ref/bugs/justify-hanging-indent.png | Bin 0 -> 1864 bytes
 tests/typ/bugs/justify-hanging-indent.typ |   6 ++++++
 3 files changed, 15 insertions(+), 3 deletions(-)
 create mode 100644 tests/ref/bugs/justify-hanging-indent.png
 create mode 100644 tests/typ/bugs/justify-hanging-indent.typ

diff --git a/crates/typst-library/src/layout/par.rs b/crates/typst-library/src/layout/par.rs
index ee47b5799..9255124e3 100644
--- a/crates/typst-library/src/layout/par.rs
+++ b/crates/typst-library/src/layout/par.rs
@@ -1015,9 +1015,15 @@ fn linebreak_optimized<'a>(vt: &Vt, p: &'a Preparation<'a>, width: Abs) -> Vec<L
                 // The line is overfull. This is the case if
                 // - justification is on, but we'd need to shrink too much
                 // - justification is off and the line just doesn't fit
-                // Since any longer line will also be overfull, we can deactivate
-                // this breakpoint.
-                active = i + 1;
+                //
+                // If this is the earliest breakpoint in the active set
+                // (active == i), remove it from the active set. If there is an
+                // earlier one (active < i), then the logically shorter line was
+                // in fact longer (can happen with negative spacing) and we
+                // can't trim the active set just yet.
+                if active == i {
+                    active += 1;
+                }
                 MAX_COST
             } else if mandatory || eof {
                 // This is a mandatory break and the line is not overfull, so
diff --git a/tests/ref/bugs/justify-hanging-indent.png b/tests/ref/bugs/justify-hanging-indent.png
new file mode 100644
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diff --git a/tests/typ/bugs/justify-hanging-indent.typ b/tests/typ/bugs/justify-hanging-indent.typ
new file mode 100644
index 000000000..511aa172e
--- /dev/null
+++ b/tests/typ/bugs/justify-hanging-indent.typ
@@ -0,0 +1,6 @@
+// Test that combination of justification and hanging indent doesn't result in
+// an underfull first line.
+
+---
+#set par(hanging-indent: 2.5cm, justify: true)
+#lorem(5)