From 6b192f58ce802b9d54e87e040d4bf5242bd5d747 Mon Sep 17 00:00:00 2001
From: NetterSilver <133535268+Silvertree2010@users.noreply.github.com>
Date: Sun, 18 Oct 2026 10:41:20 +0200
Subject: [PATCH] Clamp negative margins before checking they leave text room
 (#1941)

Found while testing crates/engine/src/cmd/page.rs:392 (margins) and :424 (margins_fit)

Co-authored-by: Claude Haiku 5.5 <noreply@anthropic.com>
---
 crates/engine/src/cmd/page.rs | 14 ++++++++------
 crates/engine/src/tests.rs    | 14 ++++++++++++++
 2 files changed, 22 insertions(+), 6 deletions(-)

diff --git a/crates/engine/src/cmd/page.rs b/crates/engine/src/cmd/page.rs
index a521fc6103..6fdfa31abe 100644
--- a/crates/engine/src/cmd/page.rs
+++ b/crates/engine/src/cmd/page.rs
@@ -474,7 +474,9 @@ fn margins(s: &mut Session, v: &Value) -> CmdResult {
             )
         }
     };
-    let gutter = p::f32(v, "gutter");
+    // Negative margins count as zero before the fit check, so one can't offset another.
+    let (t, b, l, r) = (t.max(0.0), b.max(0.0), l.max(0.0), r.max(0.0));
+    let gutter = p::f32(v, "gutter").map(|g| g.max(0.0));
     let cur = sect(s);
     if !margins_fit((cur.page_w, cur.page_h), (t, b, l, r), gutter.unwrap_or(cur.gutter)) {
         return Err(CmdError::Params("margins leave no room for text".into()));
@@ -485,12 +487,12 @@ fn margins(s: &mut Session, v: &Value) -> CmdResult {
         s.doc.settings.mirror_margins = on;
     }
     with_sect(s, |x| {
-        x.margin_top = t.max(0.0);
-        x.margin_bottom = b.max(0.0);
-        x.margin_left = l.max(0.0);
-        x.margin_right = r.max(0.0);
+        x.margin_top = t;
+        x.margin_bottom = b;
+        x.margin_left = l;
+        x.margin_right = r;
         if let Some(g) = gutter {
-            x.gutter = g.max(0.0);
+            x.gutter = g;
         }
     })
 }
diff --git a/crates/engine/src/tests.rs b/crates/engine/src/tests.rs
index 72aaa9cee3..e2a86ec6e7 100644
--- a/crates/engine/src/tests.rs
+++ b/crates/engine/src/tests.rs
@@ -1935,6 +1935,20 @@ fn layout_size_refuses_a_page_its_margins_dont_fit() {
     assert_eq!((s.doc.last_section.page_w, s.doc.last_section.page_h), (180.0, 180.0), "exactly 36 pt of room is enough");
 }
 
+/// A negative margin (or gutter) counts as zero, so it can't offset an oversized one past the
+/// text-room check: `layout.margins` refuses and changes nothing.
+#[test]
+fn layout_margins_negative_cannot_hide_an_oversized_margin() {
+    let mut s = s();
+    run(&mut s, "layout.margins", json!({"preset": "normal"}));
+    let before = s.doc.last_section.clone();
+    for v in [json!({"top": 2000, "bottom": -2000}), json!({"left": 2000, "right": -2000}), json!({"left": 600, "right": 0, "gutter": -600})] {
+        let e = s.run("layout.margins", &v).unwrap_err().to_string();
+        assert!(e.contains("margins leave no room for text"), "{v}: {e}");
+        assert_eq!(s.doc.last_section, before, "{v} changes nothing");
+    }
+}
+
 /// #1433: the smallest page there can be (0.1" wide, no margins, set straight through Page
 /// Setup's section) still lays out and exports text, a table and two columns.
 #[test]