Fix #641

Author: CppCXY

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

@@ -1240,4 +1240,22 @@ end
             "#,
         ));
     }
+
+    #[test]
+    fn test_issue_641() {
+        let mut ws = VirtualWorkspace::new_with_init_std_lib();
+        assert!(ws.check_code_for(
+            DiagnosticCode::AssignTypeMismatch,
+            r#"
+            local b --- @type boolean
+            local tar = b and 'a' or 'b'
+
+            if tar == 'a' then
+            end
+
+            --- @type 'a'|'b'
+            local _ = tar
+            "#,
+        ));
+    }
 }

crates/emmylua_code_analysis/src/semantic/infer/narrow/condition_flow/binary_flow.rs

@@ -237,16 +237,12 @@ fn maybe_var_eq_narrow(
             }
 
             let right_expr_type = infer_expr(db, cache, right_expr)?;
-            let antecedent_flow_id = get_single_antecedent(tree, flow_node)?;
-            let antecedent_type =
-                get_type_at_flow(db, tree, cache, root, &var_ref_id, antecedent_flow_id)?;
-
             let result_type = match condition_flow {
-                InferConditionFlow::TrueCondition => {
-                    narrow_down_type(db, antecedent_type, right_expr_type.clone())
-                        .unwrap_or(right_expr_type)
-                }
+                InferConditionFlow::TrueCondition => right_expr_type,
                 InferConditionFlow::FalseCondition => {
+                    let antecedent_flow_id = get_single_antecedent(tree, flow_node)?;
+                    let antecedent_type =
+                        get_type_at_flow(db, tree, cache, root, &var_ref_id, antecedent_flow_id)?;
                     TypeOps::Remove.apply(db, &antecedent_type, &right_expr_type)
                 }
             };
@@ -293,16 +289,12 @@ fn maybe_var_eq_narrow(
             }
 
             let right_expr_type = infer_expr(db, cache, right_expr)?;
-            let antecedent_flow_id = get_single_antecedent(tree, flow_node)?;
-            let antecedent_type =
-                get_type_at_flow(db, tree, cache, root, &var_ref_id, antecedent_flow_id)?;
-
             let result_type = match condition_flow {
-                InferConditionFlow::TrueCondition => {
-                    narrow_down_type(db, antecedent_type, right_expr_type.clone())
-                        .unwrap_or(right_expr_type)
-                }
+                InferConditionFlow::TrueCondition => right_expr_type,
                 InferConditionFlow::FalseCondition => {
+                    let antecedent_flow_id = get_single_antecedent(tree, flow_node)?;
+                    let antecedent_type =
+                        get_type_at_flow(db, tree, cache, root, &var_ref_id, antecedent_flow_id)?;
                     TypeOps::Remove.apply(db, &antecedent_type, &right_expr_type)
                 }
             };