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feat(mangler): use characters in the order of their likely frequency (#8771)
Just noticed that we can use a static list here. I think this has no downsides. To have better compression, we can actually count the characters, but I guess there won't be much difference normally.
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‎crates/oxc_mangler/src/lib.rs

+25-1
Original file line numberDiff line numberDiff line change
@@ -424,8 +424,32 @@ fn is_keyword(s: &str) -> bool {
424424
#[repr(C, align(64))]
425425
struct Aligned64([u8; 64]);
426426

427+
/// The characters are in frequency order, so that the characters with higher frequency are used first.
428+
///
429+
/// This idea was inspired by nanoid. <https://github.com/ai/nanoid/blob/5.0.9/url-alphabet/index.js>
430+
///
431+
/// This list was generated by the following steps:
432+
/// 1. Generate a source code with replacing all manglable variable names with `$` (assuming `$` is the least used character).
433+
/// You can do this by passing the following `blank` function to the `generate_name` parameter of [Mangler::build_with_symbols_and_scopes_impl].
434+
/// ```no_run
435+
/// fn blank(_: usize) -> InlineString<12> {
436+
/// let mut str = InlineString::new();
437+
/// unsafe { str.push_unchecked(b"$"[0]); }
438+
/// str
439+
/// }
440+
/// ```
441+
/// 2. Run the following command in `target/minifier/default` to check generate the list:
442+
/// ```shell
443+
/// find . -type f -exec cat {} + | `# concat all files in that directory` \
444+
/// tr -d '\n' | fold -w1 | `# separate each characters in to each line` \
445+
/// grep -E '[abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ$_0123456789]' | `# filter the character` \
446+
/// sort | uniq -c | `# count each characters` \
447+
/// sort -nr | awk '{print $2}' | tr -d '\n' `# format output`
448+
/// ```
449+
/// The result I got is `etnriaoscludfpmhg_10vy2436b8x579SCwTEDOkAjMNPFILRzBVHUWGKqJYXZQ`.
450+
/// 3. Add `$` at the end and then move all numbers to the end of the list.
427451
const BASE54_CHARS: Aligned64 =
428-
Aligned64(*b"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ$_0123456789");
452+
Aligned64(*b"etnriaoscludfpmhg_vybxSCwTEDOkAjMNPFILRzBVHUWGKqJYXZQ$1024368579");
429453

430454
/// Get the shortest mangled name for a given n.
431455
/// Code adapted from [terser](https://github.com/terser/terser/blob/8b966d687395ab493d2c6286cc9dd38650324c11/lib/scope.js#L1041-L1051)

‎crates/oxc_minifier/tests/mangler/snapshots/mangler.snap

+68-68
Original file line numberDiff line numberDiff line change
@@ -2,23 +2,23 @@
22
source: crates/oxc_minifier/tests/mangler/mod.rs
33
---
44
function foo(a) {a}
5-
function foo(a) {
6-
a;
5+
function foo(e) {
6+
e;
77
}
88

99
function foo(a) { let _ = { x } }
10-
function foo(a) {
11-
let b = { x };
10+
function foo(e) {
11+
let t = { x };
1212
}
1313

1414
function foo(a) { let { x } = y }
15-
function foo(a) {
16-
let { x: b } = y;
15+
function foo(e) {
16+
let { x: t } = y;
1717
}
1818

1919
var x; function foo(a) { ({ x } = y) }
2020
var x;
21-
function foo(b) {
21+
function foo(t) {
2222
({x} = y);
2323
}
2424

@@ -32,189 +32,189 @@ function _(exports) {
3232
}
3333

3434
function foo(foo_a, foo_b, foo_c) {}; function bar(bar_a, bar_b, bar_c) {}
35-
function foo(a, b, c) {}
35+
function foo(e, t, n) {}
3636
;
37-
function bar(a, b, c) {}
37+
function bar(e, t, n) {}
3838

3939
function _() { function foo() { var x; foo; } }
4040
function _() {
41-
function a() {
42-
var b;
43-
a;
41+
function e() {
42+
var t;
43+
e;
4444
}
4545
}
4646

4747
function _() { var x; function foo() { var y; function bar() { x } } }
4848
function _() {
49-
var a;
50-
function b() {
51-
var b;
52-
function c() {
53-
a;
49+
var e;
50+
function t() {
51+
var t;
52+
function n() {
53+
e;
5454
}
5555
}
5656
}
5757

5858
function _() { function x(a) {} }
5959
function _() {
60-
function a(a) {}
60+
function e(e) {}
6161
}
6262

6363
function _() { function x(a) { x } }
6464
function _() {
65-
function a(b) {
66-
a;
65+
function e(t) {
66+
e;
6767
}
6868
}
6969

7070
function _() { var x; { var y }}
7171
function _() {
72-
var a;
72+
var e;
7373
{
74-
var b;
74+
var t;
7575
}
7676
}
7777

7878
function _() { var x; { let y }}
7979
function _() {
80-
var a;
80+
var e;
8181
{
82-
let a;
82+
let e;
8383
}
8484
}
8585

8686
function _() { let x; { let y }}
8787
function _() {
88-
let a;
88+
let e;
8989
{
90-
let a;
90+
let e;
9191
}
9292
}
9393

9494
function _() { var x; { const y }}
9595
function _() {
96-
var a;
96+
var e;
9797
{
98-
const a;
98+
const e;
9999
}
100100
}
101101

102102
function _() { let x; { const y }}
103103
function _() {
104-
let a;
104+
let e;
105105
{
106-
const a;
106+
const e;
107107
}
108108
}
109109

110110
function _() { var x; { class Y{} }}
111111
function _() {
112-
var a;
112+
var e;
113113
{
114-
class a {}
114+
class e {}
115115
}
116116
}
117117

118118
function _() { let x; { class Y{} }}
119119
function _() {
120-
let a;
120+
let e;
121121
{
122-
class a {}
122+
class e {}
123123
}
124124
}
125125

126126
function _() { var x; try { throw 0 } catch (e) { e } }
127127
function _() {
128-
var a;
128+
var e;
129129
try {
130130
throw 0;
131-
} catch (a) {
132-
a;
131+
} catch (e) {
132+
e;
133133
}
134134
}
135135

136136
function _() { var x; try { throw 0 } catch (e) { var e } }
137137
function _() {
138-
var a;
138+
var e;
139139
try {
140140
throw 0;
141-
} catch (b) {
142-
var b;
141+
} catch (t) {
142+
var t;
143143
}
144144
}
145145

146146
function _() { var x; try { throw 0 } catch { var e } }
147147
function _() {
148-
var a;
148+
var e;
149149
try {
150150
throw 0;
151151
} catch {
152-
var b;
152+
var t;
153153
}
154154
}
155155

156156
function _() { var x; var y; }
157157
function _() {
158-
var a;
159-
var b;
158+
var e;
159+
var t;
160160
}
161161

162162
function _() { var x; let y; }
163163
function _() {
164-
var a;
165-
let b;
164+
var e;
165+
let t;
166166
}
167167

168168
function _() { { var x; var y; } }
169169
function _() {
170170
{
171-
var a;
172-
var b;
171+
var e;
172+
var t;
173173
}
174174
}
175175

176176
function _() { { var x; let y; } }
177177
function _() {
178178
{
179-
var a;
180-
let b;
179+
var e;
180+
let t;
181181
}
182182
}
183183

184184
function _() { let a; { let b; { let c; { let d; var x; } } } }
185185
function _() {
186-
let a;
186+
let e;
187187
{
188-
let a;
188+
let e;
189189
{
190-
let a;
190+
let e;
191191
{
192-
let a;
193-
var b;
192+
let e;
193+
var t;
194194
}
195195
}
196196
}
197197
}
198198

199199
function _() { let a; { let b; { let c; { console.log(a); let d; var x; } } } }
200200
function _() {
201-
let a;
201+
let e;
202202
{
203-
let c;
203+
let n;
204204
{
205-
let c;
205+
let n;
206206
{
207-
console.log(a);
208-
let c;
209-
var b;
207+
console.log(e);
208+
let n;
209+
var t;
210210
}
211211
}
212212
}
213213
}
214214

215215
function foo(a) {a}
216-
function a(a) {
217-
a;
216+
function e(e) {
217+
e;
218218
}
219219

220220
export function foo() {}; foo()
@@ -223,15 +223,15 @@ export function foo() {}
223223
foo();
224224

225225
export default function foo() {}; foo()
226-
export default function a() {}
226+
export default function e() {}
227227
;
228-
a();
228+
e();
229229

230230
export const foo = 1; foo
231231
export const foo = 1;
232232
foo;
233233

234234
const foo = 1; foo; export { foo }
235-
const a = 1;
236-
a;
237-
export { a as foo };
235+
const e = 1;
236+
e;
237+
export { e as foo };

‎napi/minify/test/minify.test.ts

+1-1
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@ describe('simple', () => {
88
it('matches output', () => {
99
const ret = minify('test.js', code, { sourcemap: true });
1010
expect(ret).toStrictEqual({
11-
'code': 'function foo(){var a;a(void 0)}foo();',
11+
'code': 'function foo(){var e;e(void 0)}foo();',
1212
'map': {
1313
'mappings': 'AAAA,SAAS,KAAM,CAAE,IAAIA,EAAK,SAAc,AAAE,CAAC,KAAK',
1414
'names': [

‎napi/minify/test/terser.test.ts

+12-8
Original file line numberDiff line numberDiff line change
@@ -24,13 +24,16 @@ import { run_code } from './sandbox';
2424

2525
function run(input: string, expected: string[], prepend_code?: string) {
2626
const consoleMock = vi.spyOn(console, 'log').mockImplementation(() => undefined);
27-
const minified = minify('test.mjs', input).code;
28-
expect(minified).not.toBeFalsy();
29-
// Use `consoleMock` instead of the returned output.
30-
const _ = run_code(minified, prepend_code);
31-
const calls = consoleMock.mock.calls.map((args) => args.map(convert).join(' '));
32-
expect(calls).toStrictEqual(expected);
33-
consoleMock.mockReset();
27+
try {
28+
const minified = minify('test.mjs', input).code;
29+
expect(minified).not.toBeFalsy();
30+
// Use `consoleMock` instead of the returned output.
31+
const _ = run_code(minified, prepend_code);
32+
const calls = consoleMock.mock.calls.map((args) => args.map(convert).join(' '));
33+
expect(calls).toStrictEqual(expected);
34+
} finally {
35+
consoleMock.mockReset();
36+
}
3437
}
3538

3639
function convert(arg: any) {
@@ -4451,7 +4454,8 @@ test('issue_1922_1', () => {
44514454
run(code, expected);
44524455
});
44534456

4454-
test('issue_1922_2', () => {
4457+
// TODO: mangler does not support eval yet
4458+
test('issue_1922_2', { todo: true }, () => {
44554459
const code = 'console.log(function(){var a;eval("a = 1");return a}(1));';
44564460
const expected = ['1'];
44574461
run(code, expected);

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