If the variable is mutable, it degrades to a regular type.

Fix #472

Author: CppCXY

crates/emmylua_code_analysis/src/compilation/analyzer/bind_type/mod.rs

@@ -11,11 +11,39 @@ use crate::{
 pub fn bind_type(
     db: &mut DbIndex,
     type_owner: LuaTypeOwner,
-    type_cache: LuaTypeCache,
+    mut type_cache: LuaTypeCache,
 ) -> Option<()> {
     let decl_type_cache = db.get_type_index().get_type_cache(&type_owner);
 
     if decl_type_cache.is_none() {
+        // type backward
+        if type_cache.is_infer() {
+            if let LuaTypeOwner::Decl(decl_id) = &type_owner {
+                if let Some(refs) = db
+                    .get_reference_index()
+                    .get_decl_references(&decl_id.file_id, decl_id)
+                {
+                    if refs.iter().any(|it| it.is_write) {
+                        match &type_cache.as_type() {
+                            LuaType::IntegerConst(_) => {
+                                type_cache = LuaTypeCache::InferType(LuaType::Integer)
+                            }
+                            LuaType::StringConst(_) => {
+                                type_cache = LuaTypeCache::InferType(LuaType::String)
+                            }
+                            LuaType::BooleanConst(_) => {
+                                type_cache = LuaTypeCache::InferType(LuaType::Boolean)
+                            }
+                            LuaType::FloatConst(_) => {
+                                type_cache = LuaTypeCache::InferType(LuaType::Number)
+                            }
+                            _ => {}
+                        }
+                    }
+                }
+            }
+        }
+
         db.get_type_index_mut()
             .bind_type(type_owner.clone(), type_cache);
         migrate_global_members_when_type_resolve(db, type_owner);

crates/emmylua_code_analysis/src/compilation/test/flow.rs

@@ -716,4 +716,31 @@ end
         "#,
         ));
     }
+
+    #[test]
+    fn test_issue_472() {
+        let mut ws = VirtualWorkspace::new();
+
+        assert!(ws.check_code_for(
+            DiagnosticCode::UnnecessaryIf,
+            r#"
+            worldLightLevel = 0
+            worldLightColor = 0
+            Gmae = {}
+            ---@param color integer
+            ---@param level integer
+            function Game.setWorldLight(color, level)
+                local previousColor = worldLightColor
+                local previousLevel = worldLightLevel
+
+                worldLightColor = color
+                worldLightLevel = level
+
+                if worldLightColor ~= previousColor or worldLightLevel ~= previousLevel then
+                    -- Do something...
+                end
+            end
+            "#
+        ))
+    }
 }

crates/emmylua_code_analysis/src/db_index/type/type_owner.rs

@@ -61,6 +61,14 @@ impl LuaTypeCache {
             LuaTypeCache::InferType(ty) => ty,
         }
     }
+
+    pub fn is_infer(&self) -> bool {
+        matches!(self, LuaTypeCache::InferType(_))
+    }
+
+    pub fn is_doc(&self) -> bool {
+        matches!(self, LuaTypeCache::DocType(_))
+    }
 }
 
 impl std::ops::Deref for LuaTypeCache {