Expose linear units through DXF drawing builder

crates/dxf/src/model/write.rs

@@ -1414,8 +1414,6 @@ pub struct Drawing<'a> {
     pub insunits: i64,
     /// `$MEASUREMENT`: metric (R2000 and later).
     pub metric: bool,
-    /// `$LUNITS` (linear display format), when the caller needs a non-default value.
-    pub linear_units: Option<i64>,
     /// `[x0, y0, x1, y1]` of the content: `$EXTMIN`/`$EXTMAX`, and the view the file opens at.
     pub extents: [f64; 4],
     /// `$LIMMIN`/`$LIMMAX`.
@@ -1457,7 +1455,6 @@ impl Default for Drawing<'_> {
             code_page: String::new(),
             insunits: 0,
             metric: true,
-            linear_units: None,
             extents: [0.0, 0.0, 1.0, 1.0],
             limits: [0.0, 0.0, 420.0, 297.0],
             header: Vec::new(),
@@ -1481,6 +1478,13 @@ const MODEL: &str = "*Model_Space";
 const PAPER: &str = "*Paper_Space";
 
 impl Drawing<'_> {
+    /// Set `$LUNITS` without making callers construct low-level group tags.
+    pub fn with_linear_units(mut self, units: i64) -> Self {
+        self.header.retain(|(name, _)| !name.eq_ignore_ascii_case("$LUNITS"));
+        self.header.push(("$LUNITS".into(), vec![Tag::i(70, units)]));
+        self
+    }
+
     /// The whole file as tags, ending with `0 EOF`, and how many entities were left out
     /// ([`EntityKind::Other`], and a MULTILEADER before 2007 or an ACAD_TABLE before 2004, which it has no groups for: pass
     /// those in `raw_entities`).
@@ -1627,9 +1631,6 @@ impl Drawing<'_> {
             vars.push(("$INSUNITS", vec![Tag::i(70, self.insunits)]));
             vars.push(("$MEASUREMENT", vec![Tag::i(70, i64::from(self.metric))]));
         }
-        if let Some(linear_units) = self.linear_units {
-            vars.push(("$LUNITS", vec![Tag::i(70, linear_units)]));
-        }
         w.section("HEADER");
         let given = |name: &str| self.header.iter().any(|(n, _)| n.eq_ignore_ascii_case(name));
         // The version and the handle seed are the writer's to say.

crates/dxf/tests/model_write.rs

@@ -586,7 +586,6 @@ fn the_file_around_the_content() {
         ],
         raw_entities: raw,
         extents: [0.0, 0.0, 100.0, 50.0],
-        linear_units: Some(2),
         header: vec![
             ("$LTSCALE".into(), vec![Tag::f(40, 2.0)]),
             ("$INSUNITS".into(), vec![Tag::i(70, 6)]),
@@ -597,7 +596,8 @@ fn the_file_around_the_content() {
         raw_objects: vec![Tag::s(0, "DICTIONARY"), Tag::s(5, "901"), Tag::s(330, "A")],
         raw_classes: vec![Tag::s(0, "CLASS"), Tag::s(1, "IMAGEDEF")],
         ..Drawing::default()
-    };
+    }
+    .with_linear_units(2);
     let (tags, skipped) = drawing.tags();
     assert_eq!(skipped, 1, "the entity with no groups to write");
     assert_eq!(tags.last().map(|t| (t.code, t.str())), Some((0, "EOF".to_string())));