fix(es/minifier): Make AST compressor respect toplevel (#6775)

**Related issue:**

 - Closes #4386.

Author: kdy1

crates/swc_ecma_minifier/src/compress/optimize/inline.rs

@@ -29,7 +29,7 @@ where
         &mut self,
         ident: &mut Ident,
         init: &mut Expr,
-        should_preserve: bool,
+        mut should_preserve: bool,
         can_drop: bool,
     ) {
         trace_op!(
@@ -58,6 +58,7 @@ where
             if !usage.var_initialized {
                 return;
             }
+
             if self.data.top.used_arguments && usage.declared_as_fn_param {
                 return;
             }
@@ -95,6 +96,8 @@ where
             let is_inline_enabled =
                 self.options.reduce_vars || self.options.collapse_vars || self.options.inline != 0;
 
+            should_preserve |= !self.options.top_level() && usage.is_top_level;
+
             self.vars.inline_with_multi_replacer(init);
 
             // We inline arrays partially if it's pure (all elements are literal), and not

crates/swc_ecma_minifier/src/program_data.rs

@@ -121,6 +121,9 @@ pub(crate) struct VarUsageInfo {
 
     pub(crate) pure_fn: bool,
 
+    /// Is the variable declared in top level?
+    pub(crate) is_top_level: bool,
+
     /// `infects_to`. This should be renamed, but it will be done with another
     /// PR. (because it's hard to review)
     infects: Vec<Access>,
@@ -168,6 +171,7 @@ impl Default for VarUsageInfo {
             used_in_non_child_fn: Default::default(),
             accessed_props: Default::default(),
             used_recursively: Default::default(),
+            is_top_level: Default::default(),
         }
     }
 }
@@ -346,6 +350,7 @@ impl Storage for ProgramData {
         // }
 
         let v = self.vars.entry(i.to_id()).or_default();
+        v.is_top_level |= ctx.is_top_level;
 
         if has_init && (v.declared || v.var_initialized) {
             #[cfg(feature = "debug")]

crates/swc_ecma_minifier/tests/fixture/issues/4386/1/config.json

@@ -0,0 +1,4 @@
+{
+    "defaults": true,
+    "toplevel": false
+}

crates/swc_ecma_minifier/tests/fixture/issues/4386/1/input.js

@@ -0,0 +1,24 @@
+var application;
+(() => {
+        var __webpack_require__ = {};
+        (() => {
+                __webpack_require__.d = (exports, definition) => {
+                };
+        })();
+        (() => {
+                __webpack_require__.o = (obj, prop) => { };
+        })();
+        (() => {
+                __webpack_require__.r = (exports) => {
+                };
+        })();
+        var __webpack_exports__ = {};
+        __webpack_require__.r(__webpack_exports__);
+        __webpack_require__.d(__webpack_exports__, {
+                "bootstrap": () => (bootstrap)
+        });
+        function bootstrap() {
+                alert();
+        }
+        application = __webpack_exports__;
+})();

crates/swc_ecma_minifier/tests/fixture/issues/4386/1/output.js

@@ -0,0 +1,12 @@
+var application;
+(()=>{
+    var __webpack_require__ = {};
+    __webpack_require__.d = (exports, definition)=>{}, __webpack_require__.o = (obj, prop)=>{}, __webpack_require__.r = (exports)=>{};
+    var __webpack_exports__ = {};
+    function bootstrap() {
+        alert();
+    }
+    __webpack_require__.r(__webpack_exports__), __webpack_require__.d(__webpack_exports__, {
+        bootstrap: ()=>bootstrap
+    }), application = __webpack_exports__;
+})();

crates/swc_ecma_minifier/tests/fixture/issues/4386/2/config.json

@@ -0,0 +1,4 @@
+{
+    "defaults": true,
+    "toplevel": true
+}

crates/swc_ecma_minifier/tests/fixture/issues/4386/2/input.js

@@ -0,0 +1,24 @@
+var application;
+(() => {
+        var __webpack_require__ = {};
+        (() => {
+                __webpack_require__.d = (exports, definition) => {
+                };
+        })();
+        (() => {
+                __webpack_require__.o = (obj, prop) => { };
+        })();
+        (() => {
+                __webpack_require__.r = (exports) => {
+                };
+        })();
+        var __webpack_exports__ = {};
+        __webpack_require__.r(__webpack_exports__);
+        __webpack_require__.d(__webpack_exports__, {
+                "bootstrap": () => (bootstrap)
+        });
+        function bootstrap() {
+                alert();
+        }
+        application = __webpack_exports__;
+})();

crates/swc_ecma_minifier/tests/fixture/issues/4386/2/output.js

@@ -0,0 +1,11 @@
+(()=>{
+    var __webpack_require__ = {};
+    __webpack_require__.d = (exports, definition)=>{}, __webpack_require__.o = (obj, prop)=>{}, __webpack_require__.r = (exports)=>{};
+    var __webpack_exports__ = {};
+    function bootstrap() {
+        alert();
+    }
+    __webpack_require__.r(__webpack_exports__), __webpack_require__.d(__webpack_exports__, {
+        bootstrap: ()=>bootstrap
+    });
+})();

crates/swc_ecma_minifier/tests/fixture/projects/next/config.json

@@ -0,0 +1,4 @@
+{
+    "defaults": true,
+    "toplevel": true
+}

crates/swc_ecma_transforms_optimization/src/simplify/dce/mod.rs

@@ -633,6 +633,14 @@ impl TreeShaker {
             } else if !self.in_block_stmt {
                 return false;
             }
+
+            // Abort if the variable is declared on top level scope.
+            let ix = self.data.graph_ix.get_index_of(&name);
+            if let Some(ix) = ix {
+                if self.data.entries.contains(&(ix as u32)) {
+                    return false;
+                }
+            }
         }
 
         if self.config.top_retain.contains(&name.0) {

crates/swc_ecma_usage_analyzer/src/analyzer/ctx.rs

@@ -21,6 +21,7 @@ where
 }
 
 #[derive(Debug, Default, Clone, Copy)]
+#[non_exhaustive]
 pub struct Ctx {
     /// See [crate::marks::Marks]
     pub skip_standalone: bool,
@@ -60,6 +61,8 @@ pub struct Ctx {
     pub inline_prevented: bool,
 
     pub is_op_assign: bool,
+
+    pub is_top_level: bool,
 }
 
 pub(super) struct WithCtx<'a, S>

crates/swc_ecma_usage_analyzer/src/analyzer/mod.rs

@@ -79,7 +79,10 @@ where
         let mut child = UsageAnalyzer {
             data: Default::default(),
             marks: self.marks,
-            ctx: self.ctx,
+            ctx: Ctx {
+                is_top_level: false,
+                ..self.ctx
+            },
             scope: Default::default(),
             used_recursively: self.used_recursively.clone(),
         };
@@ -849,6 +852,7 @@ where
     fn visit_module(&mut self, n: &Module) {
         let ctx = Ctx {
             skip_standalone: true,
+            is_top_level: true,
             ..self.ctx
         };
         n.visit_children_with(&mut *self.with_ctx(ctx))
@@ -857,6 +861,7 @@ where
     fn visit_script(&mut self, n: &Script) {
         let ctx = Ctx {
             skip_standalone: true,
+            is_top_level: true,
             ..self.ctx
         };
         n.visit_children_with(&mut *self.with_ctx(ctx))