feat(es/minifier): Improve simplification of ?. (#6681)

**Related issue:**

 - Closes https://github.com/swc-project/swc/issues/6492.

crates/swc_ecma_minifier/src/compress/pure/misc.rs

@@ -364,6 +364,30 @@ impl Pure<'_> {
         }
     }
 
+    pub(super) fn optimize_opt_chain(&mut self, e: &mut Expr) {
+        let opt = match e {
+            Expr::OptChain(c) => c,
+            _ => return,
+        };
+
+        if let OptChainBase::Member(base) = &mut opt.base {
+            if match &*base.obj {
+                Expr::Lit(Lit::Null(..)) => false,
+                Expr::Lit(..) | Expr::Object(..) | Expr::Array(..) => true,
+                _ => false,
+            } {
+                self.changed = true;
+                report_change!("Optimized optional chaining expression where object is not null");
+
+                *e = Expr::Member(MemberExpr {
+                    span: opt.span,
+                    obj: base.obj.take(),
+                    prop: base.prop.take(),
+                });
+            }
+        }
+    }
+
     /// new Array(...) -> Array(...)
     pub(super) fn optimize_builtin_object(&mut self, e: &mut Expr) {
         if !self.options.pristine_globals {

crates/swc_ecma_minifier/src/compress/pure/mod.rs

@@ -551,6 +551,12 @@ impl VisitMut for Pure<'_> {
         if e.is_seq() {
             debug_assert_valid(e);
         }
+
+        self.optimize_opt_chain(e);
+
+        if e.is_seq() {
+            debug_assert_valid(e);
+        }
     }
 
     fn visit_mut_expr_stmt(&mut self, s: &mut ExprStmt) {

crates/swc_ecma_minifier/tests/fixture/issues/6492/1/input.js

@@ -0,0 +1,3 @@
+const obj = { key: 42 };
+const val = obj?.[null || 'key']
+console.log('val', val)

crates/swc_ecma_minifier/tests/fixture/issues/6492/1/output.js

@@ -0,0 +1 @@
+console.log('val', 42);

crates/swc_ecma_minifier/tests/fixture/issues/6492/2/input.js

@@ -0,0 +1,3 @@
+const obj = { key: 42 };
+const val = obj?.key.toString()
+console.log('val', val)

crates/swc_ecma_minifier/tests/fixture/issues/6492/2/output.js

@@ -0,0 +1 @@
+console.log('val', "42");

crates/swc_ecma_minifier/tests/fixture/issues/6492/3/input.js

@@ -0,0 +1,3 @@
+const obj = { key: 42 };
+const val = obj?.key?.toString()
+console.log('val', val)

crates/swc_ecma_minifier/tests/fixture/issues/6492/3/output.js

@@ -0,0 +1 @@
+console.log('val', "42");

crates/swc_ecma_minifier/tests/fixture/issues/6492/4/input.js

@@ -0,0 +1,3 @@
+const obj = { key: 42 };
+const val = obj.key?.toString()
+console.log('val', val)

crates/swc_ecma_minifier/tests/fixture/issues/6492/4/output.js

@@ -0,0 +1 @@
+console.log('val', "42");