From ba351201bca9bb116c2216b3e3f031cb8000b144 Mon Sep 17 00:00:00 2001
From: Miquel Sabaté Solà <mikisabate@gmail.com>
Date: Mon, 18 Aug 2025 17:08:53 +0200
Subject: Don't get into all blocks when evaluating the context
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For some control statements like .if/.ifdef/.ifndef this is only desired
when the condition is true; otherwise getting into the inner block
should be prevented.

Signed-off-by: Miquel Sabaté Solà <mikisabate@gmail.com>
---
 lib/xixanta/src/assembler.rs | 55 ++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 51 insertions(+), 4 deletions(-)

(limited to 'lib/xixanta/src')

diff --git a/lib/xixanta/src/assembler.rs b/lib/xixanta/src/assembler.rs
index 2b82008..c12773b 100644
--- a/lib/xixanta/src/assembler.rs
+++ b/lib/xixanta/src/assembler.rs
@@ -448,11 +448,33 @@ impl<'a> Assembler<'a> {
                         });
                     }
 
-                    // If this control statement actually has a body, go inside
-                    // of it.
+                    // If this control statement actually has a body, try to go
+                    // inside of it. That is not possible, for example, on
+                    // if/ifdef/ifndef conditions with a condition that
+                    // evaluates to false.
                     if control_type.has_body() {
-                        let inner = &node.right.as_ref().unwrap().args.as_ref().unwrap();
-                        self.eval_context(inner)?;
+                        match control_type {
+                            ControlType::IfDef | ControlType::IfNDef => {
+                                // NOTE: you cannot realistically evaluate a
+                                // condition which might depend on macro
+                                // arguments which have not been provided at
+                                // this stage. Hence, don't go into the inner
+                                // block if this is the case.
+                                if self.macros_seen == 0 {
+                                    self.evaluate_ifdef_block(node)?
+                                }
+                            }
+                            ControlType::If => {
+                                // NOTE: see IfDef | IfNDef.
+                                if self.macros_seen == 0 {
+                                    self.evaluate_if_block(node)?;
+                                }
+                            }
+                            _ => {
+                                let inner = &node.right.as_ref().unwrap().args.as_ref().unwrap();
+                                self.eval_context(inner)?;
+                            }
+                        };
                     }
                 }
                 _ => {}
@@ -1649,6 +1671,8 @@ impl<'a> Assembler<'a> {
                 source: self.source_for(node),
                 global: false,
             });
+        } else if self.stage == Stage::Context {
+            self.eval_context(inner)?;
         } else {
             self.bundle(inner)?;
         }
@@ -3631,6 +3655,29 @@ JAL procedure
         }
     }
 
+    #[test]
+    fn dont_redefine_variables_inside_false_ifdefs() {
+        let res = just_bundles(
+            r#"Var = 1
+.ifndef Var
+  Var = 0
+.endif
+
+.if !.defined(Var)
+  Var = 0
+.endif
+
+lda #Var
+"#,
+        );
+
+        assert_eq!(res.len(), 1);
+
+        assert_eq!(res[0].size, 2);
+        assert_eq!(res[0].bytes[0], 0xA9);
+        assert_eq!(res[0].bytes[1], 0x01);
+    }
+
     // Macros
 
     #[test]
-- 
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