fix nested matches

crates/lean_compiler/src/b_compile_intermediate.rs

@@ -9,6 +9,7 @@ struct Compiler {
     match_blocks: Vec<MatchBlock>,
     if_counter: usize,
     call_counter: usize,
+    match_counter: usize,
     func_name: String,
     stack_frame_layout: StackFrameLayout,
     args_count: usize,
@@ -210,8 +211,9 @@ fn compile_lines(
             SimpleLine::Match { value, arms } => {
                 compiler.stack_frame_layout.scopes.push(ScopeLayout::default());
 
-                let match_index = compiler.match_blocks.len();
-                let end_label = Label::match_end(match_index);
+                let label_id = compiler.match_counter;
+                compiler.match_counter += 1;
+                let end_label = Label::match_end(label_id);
 
                 let value_simplified = IntermediateValue::from_simple_expr(value, compiler);
 
@@ -232,6 +234,8 @@ fn compile_lines(
                     function_name: function_name.clone(),
                     match_cases: compiled_arms,
                 });
+                // Get the actual index AFTER pushing (nested matches may have pushed their blocks first)
+                let match_index = compiler.match_blocks.len() - 1;
 
                 let value_scaled_offset = IntermediateValue::MemoryAfterFp {
                     offset: compiler.stack_pos.into(),
@@ -263,9 +267,9 @@ fn compile_lines(
                 compiler.bytecode.insert(end_label, remaining);
 
                 compiler.stack_frame_layout.scopes.pop();
-                compiler.stack_pos = saved_stack_pos;
-                // It is not necessary to update compiler.stack_size here because the preceding call to
-                // compile lines should have done so.
+                // Don't reset stack_pos here - we need to preserve space for the temps we allocated.
+                // Nested matches would otherwise reuse the same temp positions, causing conflicts.
+                // This is consistent with IfNotZero which also doesn't reset stack_pos.
 
                 return Ok(instructions);
             }

crates/lean_compiler/tests/test_compiler.rs

@@ -1455,3 +1455,159 @@ fn test_len_2d_array() {
         false,
     );
 }
+
+#[test]
+fn test_nested_matches() {
+    let program = r#"
+    fn main() {
+        assert test_func(0, 0) == 6;
+        assert test_func(1, 0) == 3;
+        return;
+    }
+
+    fn test_func(a, b) -> 1 {
+        x = 1;
+
+        var mut_x_2;
+        match a {
+            0 => {            
+                var mut_x_1;
+                mut_x_1 = x + 2;
+                match b {
+                    0 => {                    
+                        mut_x_2 = mut_x_1 + 3;
+                    }
+                }
+            }
+            1 => {
+                mut_x_2 = x + 2;
+            }
+        }
+
+        return mut_x_2;
+    }
+    "#;
+    compile_and_run(
+        &ProgramSource::Raw(program.to_string()),
+        (&[], &[]),
+        DEFAULT_NO_VEC_RUNTIME_MEMORY,
+        false,
+    );
+}
+
+#[test]
+fn test_deeply_nested_match() {
+    // Test with 3 levels of nesting, multiple arms, and variables at each level
+    let program = r#"
+    fn main() {
+        // Test each combination with expected values
+        // (0,0,0): base=1000, local_a=5, local_b=8, inner_val=1008
+        assert compute(0, 0, 0) == 1008;
+        // (0,0,1): base=1000, local_a=5, local_b=8, inner_val=1009
+        assert compute(0, 0, 1) == 1009;
+        // (0,1,0): base=1000, local_a=5, local_b=12, inner_val=1012
+        assert compute(0, 1, 0) == 1012;
+        // (0,1,1): base=1000, local_a=5, local_b=12, inner_val=1013
+        assert compute(0, 1, 1) == 1013;
+        // (1,0,0): base=1000, local_a=16, local_b=36, inner_val=1036
+        assert compute(1, 0, 0) == 1036;
+        // (1,0,1): base=1000, local_a=16, local_b=36, inner_val=1037
+        assert compute(1, 0, 1) == 1037;
+        // (1,1,0): base=1000, local_a=16, local_b=46, inner_val=1046
+        assert compute(1, 1, 0) == 1046;
+        // (1,1,1): base=1000, local_a=16, local_b=46, inner_val=1047
+        assert compute(1, 1, 1) == 1047;
+        return;
+    }
+
+    fn compute(a, b, c) -> 1 {
+        base = 1000;
+        var outer_val;
+        var mid_val;
+        var inner_val;
+
+        match a {
+            0 => {
+                outer_val = 5;
+                var local_a;
+                local_a = a + outer_val;  // local_a = 5
+
+                match b {
+                    0 => {
+                        mid_val = 3;
+                        var local_b;
+                        local_b = local_a + mid_val;  // local_b = 8
+
+                        match c {
+                            0 => {
+                                inner_val = base + local_b + c;  // 1000 + 8 + 0 = 1008
+                            }
+                            1 => {
+                                inner_val = base + local_b + c;  // 1000 + 8 + 1 = 1009
+                            }
+                        }
+                    }
+                    1 => {
+                        mid_val = 7;
+                        var local_b;
+                        local_b = local_a + mid_val;  // local_b = 12
+
+                        match c {
+                            0 => {
+                                inner_val = base + local_b + c;  // 1000 + 12 + 0 = 1012
+                            }
+                            1 => {
+                                inner_val = base + local_b + c;  // 1000 + 12 + 1 = 1013
+                            }
+                        }
+                    }
+                }
+            }
+            1 => {
+                outer_val = 15;
+                var local_a;
+                local_a = a + outer_val;  // local_a = 16
+
+                match b {
+                    0 => {
+                        mid_val = 20;
+                        var local_b;
+                        local_b = local_a + mid_val;  // local_b = 36
+
+                        match c {
+                            0 => {
+                                inner_val = base + local_b + c;  // 1000 + 36 + 0 = 1036
+                            }
+                            1 => {
+                                inner_val = base + local_b + c;  // 1000 + 36 + 1 = 1037
+                            }
+                        }
+                    }
+                    1 => {
+                        mid_val = 30;
+                        var local_b;
+                        local_b = local_a + mid_val;  // local_b = 46
+
+                        match c {
+                            0 => {
+                                inner_val = base + local_b + c;  // 1000 + 46 + 0 = 1046
+                            }
+                            1 => {
+                                inner_val = base + local_b + c;  // 1000 + 46 + 1 = 1047
+                            }
+                        }
+                    }
+                }
+            }
+        }
+
+        return inner_val;
+    }
+    "#;
+    compile_and_run(
+        &ProgramSource::Raw(program.to_string()),
+        (&[], &[]),
+        DEFAULT_NO_VEC_RUNTIME_MEMORY,
+        false,
+    );
+}