feat(minifier): merge single var declarations without init into for-of (

#8813) for-of version of #8812.
oxc-project · Jan 31, 2025 · f02d9e9 · f02d9e9
1 parent 99b47ed
commit f02d9e9
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diff --git a/crates/oxc_minifier/src/peephole/collapse_variable_declarations.rs b/crates/oxc_minifier/src/peephole/collapse_variable_declarations.rs
@@ -225,7 +225,6 @@ mod test {
         }
 
         #[test]
-        #[ignore]
         fn test_for_of() {
             test("var a; for (a of b) foo()", "for (var a of b) foo()");
             test_same("a = 0; for (a of b) foo()");

diff --git a/crates/oxc_minifier/src/peephole/minimize_statements.rs b/crates/oxc_minifier/src/peephole/minimize_statements.rs
@@ -407,6 +407,38 @@ impl<'a> PeepholeOptimizations {
                 }
                 result.push(Statement::ForInStatement(for_in_stmt));
             }
+            Statement::ForOfStatement(mut for_of_stmt) => {
+                // "var a; for (a of b) c" => "for (var a of b) c"
+                if let Some(Statement::VariableDeclaration(prev_var_decl)) = result.last_mut() {
+                    if let ForStatementLeft::AssignmentTargetIdentifier(id) = &for_of_stmt.left {
+                        let prev_var_decl_no_init_item = {
+                            if prev_var_decl.kind.is_var()
+                                && prev_var_decl.declarations.len() == 1
+                                && prev_var_decl.declarations[0].init.is_none()
+                            {
+                                Some(&prev_var_decl.declarations[0])
+                            } else {
+                                None
+                            }
+                        };
+                        if let Some(prev_var_decl_item) = prev_var_decl_no_init_item {
+                            if let BindingPatternKind::BindingIdentifier(decl_id) =
+                                &prev_var_decl_item.id.kind
+                            {
+                                if id.name == decl_id.name {
+                                    for_of_stmt.left =
+                                        ForStatementLeft::VariableDeclaration(ctx.ast.alloc(
+                                            ctx.ast.move_variable_declaration(prev_var_decl),
+                                        ));
+                                    result.pop();
+                                    self.mark_current_function_as_changed();
+                                }
+                            }
+                        }
+                    }
+                }
+                result.push(Statement::ForOfStatement(for_of_stmt));
+            }
             stmt => result.push(stmt),
         }
     }