From 7e4f6654a4a87437c9299292bef2632d31562bef Mon Sep 17 00:00:00 2001
From: Jeff <dev@jeffa.io>
Date: Fri, 1 Nov 2024 02:51:18 -0400
Subject: [PATCH] Add move instruction to fix assignment to conditionals

---
 dust-lang/src/parser.rs         | 10 +++++
 dust-lang/src/vm.rs             |  7 +++-
 dust-lang/tests/control_flow.rs | 65 +++++++++++++++++++++++++++++++++
 3 files changed, 81 insertions(+), 1 deletion(-)

diff --git a/dust-lang/src/parser.rs b/dust-lang/src/parser.rs
index 4611086..2fe67a2 100644
--- a/dust-lang/src/parser.rs
+++ b/dust-lang/src/parser.rs
@@ -1003,11 +1003,21 @@ impl<'src> Parser<'src> {
 
         if let Token::Else = self.current_token {
             let else_start = self.chunk.len();
+            let if_last_register = self.next_register().saturating_sub(1);
 
             self.parse_else(allowed, block_allowed)?;
 
+            let else_last_register = self.next_register().saturating_sub(1);
             let else_end = self.chunk.len();
             let jump_distance = (else_end - else_start) as u8;
+
+            if if_last_register < else_last_register {
+                self.emit_instruction(
+                    Instruction::r#move(else_last_register, if_last_register),
+                    self.current_position,
+                );
+            }
+
             self.current_is_expression = if_block_is_expression
                 && self
                     .chunk
diff --git a/dust-lang/src/vm.rs b/dust-lang/src/vm.rs
index 04bb99c..4d3fe22 100644
--- a/dust-lang/src/vm.rs
+++ b/dust-lang/src/vm.rs
@@ -65,7 +65,12 @@ impl Vm {
             );
 
             match instruction.operation() {
-                Operation::Move => todo!(),
+                Operation::Move => {
+                    let to_register = instruction.a();
+                    let from_register = instruction.b();
+
+                    self.set_pointer(to_register, from_register, position)?;
+                }
                 Operation::Close => {
                     let from_register = instruction.b();
                     let to_register = instruction.c();
diff --git a/dust-lang/tests/control_flow.rs b/dust-lang/tests/control_flow.rs
index 60aa85b..73313c6 100644
--- a/dust-lang/tests/control_flow.rs
+++ b/dust-lang/tests/control_flow.rs
@@ -60,6 +60,70 @@ fn equality_assignment_short() {
     assert_eq!(run(source), Ok(Some(Value::boolean(true))));
 }
 
+#[test]
+fn if_else_assigment() {
+    let source = r#"
+        let a = if 4 == 4 {
+            1; 2; 3; 4;
+            42
+        } else {
+            1; 2; 3; 4;
+            panic()
+        };
+        a"#;
+
+    assert_eq!(
+        parse(source),
+        Ok(Chunk::with_data(
+            None,
+            vec![
+                (
+                    *Instruction::equal(true, 0, 1)
+                        .set_b_is_constant()
+                        .set_c_is_constant(),
+                    Span(22, 24)
+                ),
+                (Instruction::jump(5, true), Span(22, 24)),
+                (Instruction::load_constant(0, 2, false), Span(41, 42)),
+                (Instruction::load_constant(1, 3, false), Span(44, 45)),
+                (Instruction::load_constant(2, 4, false), Span(47, 48)),
+                (Instruction::load_constant(3, 5, false), Span(50, 51)),
+                (Instruction::load_constant(4, 6, false), Span(65, 67)),
+                (Instruction::jump(6, true), Span(138, 139)),
+                (Instruction::jump(5, true), Span(138, 139)),
+                (Instruction::load_constant(5, 7, false), Span(97, 98)),
+                (Instruction::load_constant(6, 8, false), Span(100, 101)),
+                (Instruction::load_constant(7, 9, false), Span(103, 104)),
+                (Instruction::load_constant(8, 10, false), Span(106, 107)),
+                (
+                    Instruction::call_native(9, NativeFunction::Panic, 0),
+                    Span(121, 128)
+                ),
+                (Instruction::r#move(8, 4), Span(138, 139)),
+                (Instruction::define_local(8, 0, false), Span(13, 14)),
+                (Instruction::get_local(9, 0), Span(148, 149)),
+                (Instruction::r#return(true), Span(149, 149)),
+            ],
+            vec![
+                Value::integer(4),
+                Value::integer(4),
+                Value::integer(1),
+                Value::integer(2),
+                Value::integer(3),
+                Value::integer(4),
+                Value::integer(42),
+                Value::integer(1),
+                Value::integer(2),
+                Value::integer(3),
+                Value::integer(4),
+            ],
+            vec![Local::new(Identifier::new("a"), None, false, 0, 0)]
+        )),
+    );
+
+    assert_eq!(run(source), Ok(Some(Value::integer(42))));
+}
+
 #[test]
 fn if_else_complex() {
     let source = "
@@ -91,6 +155,7 @@ fn if_else_complex() {
                 (Instruction::load_constant(5, 7, false), Span(77, 78)),
                 (Instruction::load_constant(6, 8, false), Span(80, 81)),
                 (Instruction::load_constant(7, 9, false), Span(83, 84)),
+                (Instruction::r#move(7, 3), Span(95, 95)),
                 (Instruction::r#return(true), Span(95, 95)),
             ],
             vec![