Fixes counter stepping behavior (#4631)

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

3 files changed, 16 insertions, 6 deletions

diff --git a/crates/typst/src/introspection/counter.rs b/crates/typst/src/introspection/counter.rs
index 2aefb68e..b9462e3d 100644
--- a/crates/typst/src/introspection/counter.rs
+++ b/crates/typst/src/introspection/counter.rs
@@ -685,14 +685,12 @@ impl CounterState {
     pub fn step(&mut self, level: NonZeroUsize, by: usize) {
         let level = level.get();
 
-        if self.0.len() >= level {
-            self.0[level - 1] = self.0[level - 1].saturating_add(by);
-            self.0.truncate(level);
-        }
-
         while self.0.len() < level {
-            self.0.push(1);
+            self.0.push(0);
         }
+
+        self.0[level - 1] = self.0[level - 1].saturating_add(by);
+        self.0.truncate(level);
     }
 
     /// Get the first number of the state.
diff --git a/tests/ref/outline.png b/tests/ref/outline.png
index 71dd6e1a..c0d22969 100644
--- a/tests/ref/outline.png
+++ b/tests/ref/outline.png
diff --git a/tests/suite/introspection/counter.typ b/tests/suite/introspection/counter.typ
index be17d7e0..0d2be6e2 100644
--- a/tests/suite/introspection/counter.typ
+++ b/tests/suite/introspection/counter.typ
@@ -104,3 +104,15 @@ At Beta, it was #context {
 #block(foo())
 #block(foo())
 #foo()
+
+--- issue-4626-counter-depth-skip ---
+// When we step and skip a level, the levels should be filled with zeros, not
+// with ones.
+#let c = counter("c")
+#context test(c.get(), (0,))
+#c.step(level: 4)
+#context test(c.get(), (0, 0, 0, 1))
+#c.step(level: 1)
+#context test(c.get(), (1,))
+#c.step(level: 3)
+#context test(c.get(), (1, 0, 1))