From 552d9aa344cb6db2dff1e20011411a56f92d4f06 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Donny/=EA=B0=95=EB=8F=99=EC=9C=A4?= <kdy1997.dev@gmail.com>
Date: Thu, 10 Aug 2023 11:48:35 +0900
Subject: [PATCH] fix(es/minifier): Do not drop properties used via `this`
 (#7785)

**Related issue:**

 - Closes #7783.
---
 .../fixture/issues-7xxx/7783/input/.swcrc     | 71 +++++++++++++++++++
 .../tests/fixture/issues-7xxx/7783/input/1.js | 14 ++++
 .../fixture/issues-7xxx/7783/output/1.js      |  1 +
 .../thisTypeInFunctions.2.minified.js         |  1 +
 .../src/compress/optimize/unused.rs           | 41 ++++++++++-
 .../tests/fixture/issues/7783/1/input.js      | 11 +++
 .../tests/fixture/issues/7783/1/output.js     | 11 +++
 7 files changed, 149 insertions(+), 1 deletion(-)
 create mode 100644 crates/swc/tests/fixture/issues-7xxx/7783/input/.swcrc
 create mode 100644 crates/swc/tests/fixture/issues-7xxx/7783/input/1.js
 create mode 100644 crates/swc/tests/fixture/issues-7xxx/7783/output/1.js
 create mode 100644 crates/swc_ecma_minifier/tests/fixture/issues/7783/1/input.js
 create mode 100644 crates/swc_ecma_minifier/tests/fixture/issues/7783/1/output.js

diff --git a/crates/swc/tests/fixture/issues-7xxx/7783/input/.swcrc b/crates/swc/tests/fixture/issues-7xxx/7783/input/.swcrc
new file mode 100644
index 00000000000..55c5f9dd71e
--- /dev/null
+++ b/crates/swc/tests/fixture/issues-7xxx/7783/input/.swcrc
@@ -0,0 +1,71 @@
+{
+    "jsc": {
+        "parser": {
+            "syntax": "ecmascript",
+            "jsx": true
+        },
+        "target": "es2015",
+        "loose": false,
+        "minify": {
+            "compress": {
+                "arguments": false,
+                "arrows": true,
+                "booleans": true,
+                "booleans_as_integers": false,
+                "collapse_vars": true,
+                "comparisons": true,
+                "computed_props": true,
+                "conditionals": true,
+                "dead_code": true,
+                "directives": true,
+                "drop_console": false,
+                "drop_debugger": true,
+                "evaluate": true,
+                "expression": false,
+                "hoist_funs": false,
+                "hoist_props": true,
+                "hoist_vars": false,
+                "if_return": true,
+                "join_vars": true,
+                "keep_classnames": false,
+                "keep_fargs": true,
+                "keep_fnames": false,
+                "keep_infinity": false,
+                "loops": true,
+                "negate_iife": true,
+                "properties": true,
+                "reduce_funcs": false,
+                "reduce_vars": false,
+                "side_effects": true,
+                "switches": true,
+                "typeofs": true,
+                "unsafe": false,
+                "unsafe_arrows": false,
+                "unsafe_comps": false,
+                "unsafe_Function": false,
+                "unsafe_math": false,
+                "unsafe_symbols": false,
+                "unsafe_methods": false,
+                "unsafe_proto": false,
+                "unsafe_regexp": false,
+                "unsafe_undefined": false,
+                "unused": true,
+                "const_to_let": true,
+                "pristine_globals": true
+            },
+            "mangle": {
+                "toplevel": false,
+                "keep_classnames": false,
+                "keep_fnames": false,
+                "keep_private_props": false,
+                "ie8": false,
+                "safari10": false
+            }
+        }
+    },
+    "module": {
+        "type": "es6"
+    },
+    "minify": true,
+    "isModule": true
+}
\ No newline at end of file
diff --git a/crates/swc/tests/fixture/issues-7xxx/7783/input/1.js b/crates/swc/tests/fixture/issues-7xxx/7783/input/1.js
new file mode 100644
index 00000000000..8fc302ca883
--- /dev/null
+++ b/crates/swc/tests/fixture/issues-7xxx/7783/input/1.js
@@ -0,0 +1,14 @@
+export default function Home() {
+    return (
+        <div>{foo.a}</div>
+    )
+}
+
+const foo = {
+    get a() {
+        return `a ${this.b}`;
+    },
+    get b() {
+        return `b`;
+    }
+}
diff --git a/crates/swc/tests/fixture/issues-7xxx/7783/output/1.js b/crates/swc/tests/fixture/issues-7xxx/7783/output/1.js
new file mode 100644
index 00000000000..58d2bed8bc9
--- /dev/null
+++ b/crates/swc/tests/fixture/issues-7xxx/7783/output/1.js
@@ -0,0 +1 @@
+export default function e(){return React.createElement("div",null,foo.a)}let foo={get a(){return`a ${this.b}`},get b(){return"b"}};
diff --git a/crates/swc/tests/tsc-references/thisTypeInFunctions.2.minified.js b/crates/swc/tests/tsc-references/thisTypeInFunctions.2.minified.js
index 03cbbe791a0..d6663a01356 100644
--- a/crates/swc/tests/tsc-references/thisTypeInFunctions.2.minified.js
+++ b/crates/swc/tests/tsc-references/thisTypeInFunctions.2.minified.js
@@ -28,6 +28,7 @@ function implicitThis(n) {
     return this.m + n + 12;
 }
 var impl = {
+    a: 12,
     explicitVoid2: function() {
         return _this.a;
     },
diff --git a/crates/swc_ecma_minifier/src/compress/optimize/unused.rs b/crates/swc_ecma_minifier/src/compress/optimize/unused.rs
index 1359603f915..75c5ca591b1 100644
--- a/crates/swc_ecma_minifier/src/compress/optimize/unused.rs
+++ b/crates/swc_ecma_minifier/src/compress/optimize/unused.rs
@@ -1,8 +1,10 @@
+use rustc_hash::FxHashSet;
 use swc_atoms::{js_word, JsWord};
 use swc_common::{util::take::Take, DUMMY_SP};
 use swc_ecma_ast::*;
 use swc_ecma_usage_analyzer::util::is_global_var_with_pure_property_access;
 use swc_ecma_utils::{contains_ident_ref, ExprExt};
+use swc_ecma_visit::{noop_visit_type, Visit, VisitWith};
 
 use super::Optimizer;
 #[cfg(feature = "debug")]
@@ -785,11 +787,17 @@ impl Optimizer<'_> {
             return None;
         }
 
+        let properties_used_via_this = {
+            let mut v = ThisPropertyVisitor::default();
+            obj.visit_with(&mut v);
+            v.properties
+        };
+
         let should_preserve_property = |sym: &JsWord| {
             if let "toString" = &**sym {
                 return true;
             }
-            !usage.accessed_props.contains_key(sym)
+            !usage.accessed_props.contains_key(sym) && !properties_used_via_this.contains(sym)
         };
         let should_preserve = |key: &PropName| match key {
             PropName::Ident(k) => should_preserve_property(&k.sym),
@@ -824,3 +832,34 @@ impl Optimizer<'_> {
         None
     }
 }
+
+#[derive(Default)]
+struct ThisPropertyVisitor {
+    properties: FxHashSet<JsWord>,
+
+    should_abort: bool,
+}
+
+impl Visit for ThisPropertyVisitor {
+    noop_visit_type!();
+
+    fn visit_member_expr(&mut self, e: &MemberExpr) {
+        if self.should_abort {
+            return;
+        }
+
+        e.visit_children_with(self);
+
+        if let Expr::This(..) = &*e.obj {
+            match &e.prop {
+                MemberProp::Ident(p) => {
+                    self.properties.insert(p.sym.clone());
+                }
+                MemberProp::Computed(_) => {
+                    self.should_abort = true;
+                }
+                _ => {}
+            }
+        }
+    }
+}
diff --git a/crates/swc_ecma_minifier/tests/fixture/issues/7783/1/input.js b/crates/swc_ecma_minifier/tests/fixture/issues/7783/1/input.js
new file mode 100644
index 00000000000..551c23a1198
--- /dev/null
+++ b/crates/swc_ecma_minifier/tests/fixture/issues/7783/1/input.js
@@ -0,0 +1,11 @@
+export default function Home() {
+    return React.createElement("div", null, foo.a);
+}
+const foo = {
+    get a() {
+        return `a ${this.b}`;
+    },
+    get b() {
+        return `b`;
+    }
+};
diff --git a/crates/swc_ecma_minifier/tests/fixture/issues/7783/1/output.js b/crates/swc_ecma_minifier/tests/fixture/issues/7783/1/output.js
new file mode 100644
index 00000000000..4b9c79c6b5d
--- /dev/null
+++ b/crates/swc_ecma_minifier/tests/fixture/issues/7783/1/output.js
@@ -0,0 +1,11 @@
+export default function Home() {
+    return React.createElement("div", null, foo.a);
+}
+const foo = {
+    get a () {
+        return `a ${this.b}`;
+    },
+    get b () {
+        return "b";
+    }
+};