Bring the Equal constraint to reference parity

Equal was applied through a generic gather-then-apply flow and, with the
default size-retaining solve mode, never changed anything: the solver
held both sizes and the relation could not be met. Now:

- GCEQUAL joins ECONSTRAINT and GEOMCONSTRAINT Equal; both objects are
  picked inside the command (`Select first object or [Multiple]:`,
  `Select second object:`; Multiple gathers `Select objects to make equal
  to the first:`), a selection made beforehand is not used, a miss says
  `No object found.` and re-asks, an unsupported object or the same object
  twice is reported and re-asked, a repeat is refused.
- The follower is resized in place before the relation is added: a line or
  straight polyline segment keeps its start and direction and its end
  moves to the first object's length; a circle or arc keeps its center and
  takes the radius.
- During edits the side that is not being edited follows the same rule:
  its size is not retained, its start (or center) and other vertices are
  held and its direction kept, so only its length or radius changes; a
  chain of Equal relations follows along.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

src/modules/parametric/equal.rs

@@ -0,0 +1,286 @@
+use acadrust::{EntityType, Handle};
+use glam::DVec3;
+
+use crate::command::{CadCommand, CmdOption, CmdResult};
+use crate::scene::parametric_constraints::ParametricRef;
+
+use super::HorizontalConstraintCommand;
+
+#[derive(Clone, Copy)]
+enum Step {
+    /// `Select first object or [Multiple]:`, or `Select first object:`
+    /// once Multiple was chosen.
+    First { multiple: bool },
+    /// `Select second object:` — the one that takes the first's size.
+    Second(ParametricRef),
+    /// `Select objects to make equal to the first:` — a selection set,
+    /// applied on Enter.
+    Others(ParametricRef),
+}
+
+/// Interactive front end for the Equal geometric constraint: the first
+/// object sets the size, the second (or, with Multiple, every object of a
+/// set) takes its length or radius. Picks are made inside the command; a
+/// selection made before it starts is not used.
+pub struct EqualConstraintCommand {
+    step: Step,
+    picked_entity: Option<EntityType>,
+    others: Vec<Handle>,
+}
+
+impl EqualConstraintCommand {
+    pub const NO_OBJECT: &'static str = "No object found.";
+    pub const INVALID_OBJECT: &'static str =
+        "Invalid selection for Equal. Select a line, polyline segment, circle or arc.";
+    pub const SAME_OBJECT: &'static str =
+        "The object or point is already selected. Select a different object or constraint point.";
+
+    pub fn new() -> Self {
+        Self {
+            step: Step::First { multiple: false },
+            picked_entity: None,
+            others: Vec::new(),
+        }
+    }
+
+    /// The whole line, circle or arc, or the picked straight polyline
+    /// segment.
+    pub fn picked_reference(
+        entity: &EntityType,
+        handle: Handle,
+        point: DVec3,
+    ) -> Option<ParametricRef> {
+        match entity {
+            EntityType::Line(_) | EntityType::Circle(_) | EntityType::Arc(_) => {
+                Some(ParametricRef::whole(handle))
+            }
+            EntityType::LwPolyline(_) | EntityType::Polyline2D(_) => {
+                let (source, _, _) =
+                    crate::scene::centerline::picked_source(entity, handle, point)?;
+                let index = usize::try_from(source.segment_index).ok()?;
+                HorizontalConstraintCommand::segment_is_straight(entity, index)
+                    .then_some(ParametricRef::segment(handle, index))
+            }
+            _ => None,
+        }
+    }
+
+    /// An object of a Multiple set: a whole line, circle or arc, a
+    /// one-segment polyline as its segment.
+    pub fn whole_reference(entity: &EntityType, handle: Handle) -> Option<ParametricRef> {
+        match entity {
+            EntityType::Line(_) | EntityType::Circle(_) | EntityType::Arc(_) => {
+                Some(ParametricRef::whole(handle))
+            }
+            EntityType::LwPolyline(polyline) => {
+                let count = if polyline.is_closed {
+                    polyline.vertices.len()
+                } else {
+                    polyline.vertices.len().saturating_sub(1)
+                };
+                (count == 1 && HorizontalConstraintCommand::segment_is_straight(entity, 0))
+                    .then_some(ParametricRef::segment(handle, 0))
+            }
+            EntityType::Polyline2D(polyline) => {
+                let count = if polyline.is_closed() {
+                    polyline.vertices.len()
+                } else {
+                    polyline.vertices.len().saturating_sub(1)
+                };
+                (count == 1 && HorizontalConstraintCommand::segment_is_straight(entity, 0))
+                    .then_some(ParametricRef::segment(handle, 0))
+            }
+            _ => None,
+        }
+    }
+
+    fn report(message: &str) -> CmdResult {
+        CmdResult::ReportError(message.to_string())
+    }
+
+    fn finish(first: ParametricRef, others: Vec<ParametricRef>) -> CmdResult {
+        CmdResult::AddEqualConstraint {
+            first,
+            others,
+            label: "Equal constraint",
+        }
+    }
+}
+
+impl CadCommand for EqualConstraintCommand {
+    fn name(&self) -> &'static str {
+        "GCEQUAL"
+    }
+
+    fn prompt(&self) -> String {
+        match self.step {
+            Step::First { multiple: false } => {
+                "GCEQUAL  Select first object or [Multiple]:".to_string()
+            }
+            Step::First { multiple: true } => "GCEQUAL  Select first object:".to_string(),
+            Step::Second(_) => "GCEQUAL  Select second object:".to_string(),
+            Step::Others(_) if self.others.is_empty() => {
+                "GCEQUAL  Select objects to make equal to the first:".to_string()
+            }
+            Step::Others(_) => format!(
+                "GCEQUAL  Select objects to make equal to the first ({} selected, Enter to apply):",
+                self.others.len()
+            ),
+        }
+    }
+
+    fn options(&self) -> Vec<CmdOption> {
+        matches!(self.step, Step::First { multiple: false })
+            .then(|| vec![CmdOption::new("Multiple", "M")])
+            .unwrap_or_default()
+    }
+
+    fn wants_text_input(&self) -> bool {
+        true
+    }
+
+    fn point_step_accepts_keywords(&self) -> bool {
+        matches!(self.step, Step::First { multiple: false })
+    }
+
+    fn on_text_input(&mut self, text: &str) -> Option<CmdResult> {
+        let keyword = text.trim().trim_start_matches('_').to_ascii_uppercase();
+        if matches!(self.step, Step::First { multiple: false })
+            && matches!(keyword.as_str(), "M" | "MULTIPLE")
+        {
+            self.step = Step::First { multiple: true };
+            return Some(CmdResult::NeedPoint);
+        }
+        None
+    }
+
+    fn needs_entity_pick(&self) -> bool {
+        !matches!(self.step, Step::Others(_))
+    }
+
+    fn entity_pick_accepts_points(&self) -> bool {
+        true
+    }
+
+    fn entity_pick_highlights_hover(&self) -> bool {
+        true
+    }
+
+    fn inject_before_entity_pick(&self) -> bool {
+        true
+    }
+
+    fn inject_picked_entity(&mut self, entity: EntityType) {
+        self.picked_entity = Some(entity);
+    }
+
+    fn is_selection_gathering(&self) -> bool {
+        matches!(self.step, Step::Others(_))
+    }
+
+    fn on_selection_complete(&mut self, handles: Vec<Handle>) -> CmdResult {
+        if let Step::Others(first) = self.step {
+            // The first object sets the size; it cannot also follow itself.
+            self.others = handles
+                .into_iter()
+                .filter(|handle| *handle != first.entity)
+                .collect();
+        }
+        CmdResult::NeedPoint
+    }
+
+    fn on_entity_pick(&mut self, handle: Handle, point: DVec3) -> CmdResult {
+        if handle.is_null() {
+            return Self::report(Self::NO_OBJECT);
+        }
+        let Some(entity) = self.picked_entity.take() else {
+            return CmdResult::NeedPoint;
+        };
+        let Some(reference) = Self::picked_reference(&entity, handle, point) else {
+            return Self::report(Self::INVALID_OBJECT);
+        };
+        match self.step {
+            Step::First { multiple: false } => {
+                self.step = Step::Second(reference);
+                CmdResult::NeedPoint
+            }
+            Step::First { multiple: true } => {
+                self.step = Step::Others(reference);
+                CmdResult::NeedPoint
+            }
+            Step::Second(first) => {
+                if first == reference {
+                    return Self::report(Self::SAME_OBJECT);
+                }
+                Self::finish(first, vec![reference])
+            }
+            Step::Others(_) => CmdResult::NeedPoint,
+        }
+    }
+
+    // An empty-space click while an object is asked for.
+    fn on_point(&mut self, _point: DVec3) -> CmdResult {
+        Self::report(Self::NO_OBJECT)
+    }
+
+    fn on_enter(&mut self) -> CmdResult {
+        match self.step {
+            Step::Others(first) if !self.others.is_empty() => Self::finish(
+                first,
+                self.others.iter().map(|handle| ParametricRef::whole(*handle)).collect(),
+            ),
+            _ => CmdResult::Cancel,
+        }
+    }
+
+    fn on_escape(&mut self) -> CmdResult {
+        CmdResult::Cancel
+    }
+}
+
+inventory::submit!(crate::command::CommandRegistration {
+    names: &["ECONSTRAINT", "GCEQUAL"]
+});
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use acadrust::entities::Line;
+    use acadrust::types::Vector3;
+
+    fn line() -> EntityType {
+        EntityType::Line(Line::from_points(Vector3::ZERO, Vector3::new(10.0, 0.0, 0.0)))
+    }
+
+    #[test]
+    fn two_picks_make_the_second_follow_the_first() {
+        let mut command = EqualConstraintCommand::new();
+        command.inject_picked_entity(line());
+        assert!(matches!(
+            command.on_entity_pick(Handle::new(7), DVec3::ZERO),
+            CmdResult::NeedPoint
+        ));
+        command.inject_picked_entity(line());
+        let CmdResult::AddEqualConstraint { first, others, .. } =
+            command.on_entity_pick(Handle::new(8), DVec3::ZERO)
+        else {
+            panic!("the second pick must create the constraint");
+        };
+        assert_eq!(first, ParametricRef::whole(Handle::new(7)));
+        assert_eq!(others, vec![ParametricRef::whole(Handle::new(8))]);
+    }
+
+    #[test]
+    fn multiple_applies_the_gathered_set_on_enter() {
+        let mut command = EqualConstraintCommand::new();
+        assert!(matches!(command.on_text_input("M"), Some(CmdResult::NeedPoint)));
+        command.inject_picked_entity(line());
+        command.on_entity_pick(Handle::new(7), DVec3::ZERO);
+        assert!(command.is_selection_gathering());
+        command.on_selection_complete(vec![Handle::new(7), Handle::new(8), Handle::new(9)]);
+        let CmdResult::AddEqualConstraint { others, .. } = command.on_enter() else {
+            panic!("Enter must apply the set");
+        };
+        assert_eq!(others.len(), 2);
+    }
+}

src/modules/parametric/horizontal.rs

@@ -98,7 +98,7 @@ impl HorizontalConstraintCommand {
         CmdResult::ReportError("No valid constraint point found.".to_string())
     }
 
-    fn segment_is_straight(entity: &EntityType, index: usize) -> bool {
+    pub(crate) fn segment_is_straight(entity: &EntityType, index: usize) -> bool {
         match entity {
             EntityType::LwPolyline(polyline) => polyline
                 .vertices

src/modules/parametric/mod.rs

@@ -6,6 +6,8 @@ mod coincident;
 mod concentric;
 mod constraint_bar;
 mod equal_distance;
+#[path = "equal.rs"]
+mod equal_command;
 #[path = "fixed.rs"]
 mod fixed_command;
 mod geom_constraint;
@@ -24,6 +26,7 @@ mod value;
 pub use coincident::{coincident_tool, CoincidentConstraintCommand};
 pub use concentric::ConcentricConstraintCommand;
 pub use constraint_bar::ConstraintBarOptionCommand;
+pub use equal_command::EqualConstraintCommand;
 pub use equal_distance::{equal_distance_tool, EqualDistanceConstraintCommand};
 pub use fixed_command::FixConstraintCommand;
 pub use geom_constraint::GeomConstraintCommand;

src/modules/parametric/tools.rs

@@ -166,6 +166,7 @@ inventory::submit!(crate::command::CommandRegistration {
         "QCONSTRAINT",
         "GCPERPENDICULAR",
         "ECONSTRAINT",
+        "GCEQUAL",
         "TCONSTRAINT",
         "GCCONCENTRIC",
         "NRCONSTRAINT",