From 493addc2dd810103deae05a9d19dbd3f5340b072 Mon Sep 17 00:00:00 2001
From: Marco Arnulfo <103679419+marcoarnulfo@users.noreply.github.com>
Date: Mon, 19 Oct 2026 08:31:01 +0200
Subject: [PATCH] DXF files that declare no units stay unitless when saved
 again (fixes #1209) (#1210)

---
 crates/io/src/dxf_read.rs |  2 ++
 crates/io/src/tests.rs    | 20 ++++++++++++++++++++
 2 files changed, 22 insertions(+)

diff --git a/crates/io/src/dxf_read.rs b/crates/io/src/dxf_read.rs
index 1bd7cd9c..c043842e 100644
--- a/crates/io/src/dxf_read.rs
+++ b/crates/io/src/dxf_read.rs
@@ -1655,6 +1655,8 @@ pub fn read(bytes: &[u8]) -> Result<Drawing> {
     }
     let mut d = Drawing::new_imperial();
     d.layouts.clear();
+    // A file without $INSUNITS declares no units (#1209); only new drawings take the template's.
+    d.header.set_i64("INSUNITS", 0);
     let mut rx = Rx { pstyles: plot_style_names(&secs), ..Rx::default() };
     let mut blocks: Vec<(String, Vec3, String, Vec<(Option<String>, bool, Entity)>, i64)> = Vec::new();
     let mut layout_objs: Vec<(String, u32, String, PageSetup)> = Vec::new();
diff --git a/crates/io/src/tests.rs b/crates/io/src/tests.rs
index 20a18fe5..8b7f5647 100644
--- a/crates/io/src/tests.rs
+++ b/crates/io/src/tests.rs
@@ -2502,3 +2502,23 @@ fn foreign_table_reads_cell_text_height_and_keeps_style_scale() {
     assert_eq!(t2.cells[0][0].text_height, Some(150.0));
     assert_eq!(t2.cells[0][1].text_height, None);
 }
+
+/// Issue #1209: a file that declares no units ($INSUNITS absent or 0) stays unitless when written
+/// again; only a new drawing takes its template's units.
+#[test]
+fn drawing_without_insunits_stays_unitless() {
+    let r12 = |extra: &str| {
+        format!(
+            "0\nSECTION\n2\nHEADER\n9\n$ACADVER\n1\nAC1009\n{extra}0\nENDSEC\n0\nSECTION\n2\nENTITIES\n0\nLINE\n8\n0\n10\n0\n20\n0\n11\n1\n21\n1\n0\nENDSEC\n0\nEOF\n"
+        )
+    };
+    let insunits = |text: &str| {
+        text.lines().map(str::trim).collect::<Vec<_>>().windows(3).find(|w| w[0] == "$INSUNITS" && w[1] == "70").map(|w| w[2].to_string())
+    };
+    let rewritten = |extra: &str| insunits(&write_dxf(&read_dxf(r12(extra).as_bytes()).unwrap()));
+    assert_eq!(rewritten(""), Some("0".into()), "absent");
+    assert_eq!(rewritten("9\n$INSUNITS\n70\n0\n"), Some("0".into()), "declared unitless");
+    assert_eq!(rewritten("9\n$INSUNITS\n70\n6\n"), Some("6".into()), "declared metres");
+    assert_eq!(insunits(&write_dxf(&Drawing::new_metric())), Some("4".into()));
+    assert_eq!(insunits(&write_dxf(&Drawing::new_imperial())), Some("1".into()));
+}