fix(es/minifier): Fix analysis of var declaration after usage

crates/swc/tests/exec/issues-6xxx/6039/1/exec.js

@@ -0,0 +1,26 @@
+function foo() {
+    let walker = 0;
+
+    let arr = [];
+
+    function bar(defaultValue) {
+        const myIndex = walker;
+        walker += 1;
+
+        console.log({ arr });
+
+        if (arr.length < myIndex + 1) {
+            arr[myIndex] = defaultValue;
+        }
+    }
+
+    return bar;
+}
+
+const bar = foo();
+
+bar(null);
+bar(null);
+bar(null);
+bar(null);
+bar(null);

crates/swc_ecma_minifier/src/analyzer/storage/normal.rs

@@ -157,6 +157,8 @@ impl Storage for ProgramData {
                 if v.used_in_non_child_fn {
                     v.is_fn_local = false;
                 }
+
+                v.var_initialized |= has_init;
             })
             .or_insert_with(|| VarUsageInfo {
                 is_fn_local: true,

crates/swc_ecma_minifier/src/pass/precompress.rs

@@ -34,6 +34,23 @@ impl VisitMut for PrecompressOptimizer {
         }
     }
 
+    fn visit_mut_pat_or_expr(&mut self, n: &mut PatOrExpr) {
+        n.visit_mut_children_with(self);
+
+        match n {
+            PatOrExpr::Expr(e) => {
+                if let Expr::Ident(i) = &**e {
+                    *n = PatOrExpr::Pat(i.clone().into())
+                }
+            }
+            PatOrExpr::Pat(p) => {
+                if let Pat::Expr(e) = &mut **p {
+                    *n = PatOrExpr::Expr(e.take());
+                }
+            }
+        }
+    }
+
     fn visit_mut_stmts(&mut self, n: &mut Vec<Stmt>) {
         self.maybe_par(*HEAVY_TASK_PARALLELS, n, |v, n| {
             n.visit_mut_with(v);

crates/swc_ecma_minifier/src/util/base54.rs

@@ -186,16 +186,16 @@ impl CharFreq {
             return;
         }
 
-        #[cfg(feature = "debug")]
-        {
-            let considered = s
-                .chars()
-                .filter(|&c| Ident::is_valid_continue(c))
-                .collect::<String>();
-            if !considered.is_empty() {
-                tracing::debug!("Scanning: `{}` with delta {}", considered, delta);
-            }
-        }
+        // #[cfg(feature = "debug")]
+        // {
+        //     let considered = s
+        //         .chars()
+        //         .filter(|&c| Ident::is_valid_continue(c))
+        //         .collect::<String>();
+        //     if !considered.is_empty() {
+        //         tracing::debug!("Scanning: `{}` with delta {}", considered, delta);
+        //     }
+        // }
 
         for &c in s.as_bytes() {
             match c {

crates/swc_ecma_minifier/tests/exec.rs

@@ -10140,3 +10140,66 @@ fn issue_6051() {
         "###,
     );
 }
+
+#[test]
+fn issue_6039_1() {
+    run_default_exec_test(
+        r###"
+        function foo() {
+            let walker = 0;
+
+            let arr = [];
+
+            function bar(defaultValue) {
+                const myIndex = walker;
+                walker += 1;
+
+                console.log({ arr });
+
+                if (arr.length < myIndex + 1) {
+                    arr[myIndex] = defaultValue;
+                }
+            }
+
+            return bar;
+        }
+
+        const bar = foo();
+
+        bar(null);
+        bar(null);
+        bar(null);
+        bar(null);
+        bar(null);
+        "###,
+    );
+}
+
+#[test]
+fn issue_6039_2() {
+    run_default_exec_test(
+        r###"
+        var foo = function foo() {
+            var walker = 0;
+            var arr = [];
+            function bar(defaultValue) {
+                var myIndex = walker;
+                walker += 1;
+                console.log({
+                    arr: arr
+                });
+                if (arr.length < myIndex + 1) {
+                    arr[myIndex] = defaultValue;
+                }
+            }
+            return bar;
+        };
+        var bar = foo();
+        bar(null);
+        bar(null);
+        bar(null);
+        bar(null);
+        bar(null);
+    "###,
+    );
+}

crates/swc_ecma_minifier/tests/terser/compress/negate_iife/negate_iife_2_side_effects/output.js

@@ -1 +1 @@
-({}.x = 10);
+10;