Sets the default compression to 0 (#5526)

**What's the problem this PR addresses?**

Cache compression doesn't seem the best option nowadays:

- It adds significant time to installs
- It adds a non-negligible runtime overhead (partially related, #1817)
- It prevents Git from diffing archives when they're modified

Its main advantage is for some amazingly large packages, where storing
them inside a Git repository would be impossible (GitHub has a 600MB
file limit). But since we changed the cache default to
`enableGlobalCache: true`, this isn't relevant by default, so the cache
compression should be set to zero.

One potential issue is how it may give the impression that Yarn became
worse for global cache users. We don't believe it's the case (Git can
delta uncompressed archives in some measure, making it less expensive to
upgrade from one package version to another), but to the average eye it
may not look as such.

**How did you fix it?**

This diff sets the new default compression setting to 0.

To avoid breaking projects' (or at least not making the migration more
difficult), I added a rule to automatically set `compressionLevel` (and
`enableGlobalCache`) to their 3.x default values when running `yarn
install` in a 3.x project. When users are ready they can remove these
settings and re-run the install.

I kept the current compression level on our repository to avoid changing
all archives again. I think we'll have to think of purging the
repository in some form to migrate it to `compressionLevel: 0`.

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Author: arcanis

.yarn/versions/6c7747db.yml

@@ -0,0 +1,34 @@
+releases:
+  "@yarnpkg/cli": major
+  "@yarnpkg/core": major
+  "@yarnpkg/plugin-essentials": major
+
+declined:
+  - "@yarnpkg/plugin-compat"
+  - "@yarnpkg/plugin-constraints"
+  - "@yarnpkg/plugin-dlx"
+  - "@yarnpkg/plugin-exec"
+  - "@yarnpkg/plugin-file"
+  - "@yarnpkg/plugin-git"
+  - "@yarnpkg/plugin-github"
+  - "@yarnpkg/plugin-http"
+  - "@yarnpkg/plugin-init"
+  - "@yarnpkg/plugin-interactive-tools"
+  - "@yarnpkg/plugin-link"
+  - "@yarnpkg/plugin-nm"
+  - "@yarnpkg/plugin-npm"
+  - "@yarnpkg/plugin-npm-cli"
+  - "@yarnpkg/plugin-pack"
+  - "@yarnpkg/plugin-patch"
+  - "@yarnpkg/plugin-pnp"
+  - "@yarnpkg/plugin-pnpm"
+  - "@yarnpkg/plugin-stage"
+  - "@yarnpkg/plugin-typescript"
+  - "@yarnpkg/plugin-version"
+  - "@yarnpkg/plugin-workspace-tools"
+  - "@yarnpkg/builder"
+  - "@yarnpkg/doctor"
+  - "@yarnpkg/extensions"
+  - "@yarnpkg/nm"
+  - "@yarnpkg/pnpify"
+  - "@yarnpkg/sdks"

.yarnrc.yml

@@ -1,22 +1,18 @@
 changesetIgnorePatterns:
-  - ".github/**"
-  - ".yarn/cache/**"
+  - .github/**
+  - .yarn/cache/**
   - "**/*.test.{js,ts}"
-  - "packages/*/tests/**"
-  - "packages/plugin-compat/extra/**"
-  - "packages/gatsby/**"
+  - packages/*/tests/**
+  - packages/plugin-compat/extra/**
+  - packages/gatsby/**
 
-enableGlobalCache: false
+compressionLevel: mixed
 
-pnpEnableEsmLoader: true
+enableGlobalCache: false
 
 immutablePatterns:
   - .pnp.*
 
-supportedArchitectures:
-  os: [darwin, linux, win32]
-  cpu: [x64, arm64]
-
 initScope: yarnpkg
 
 npmPublishAccess: public
@@ -73,8 +69,19 @@ packageExtensions:
       typedoc-plugin-yarn:
         optional: true
 
+pnpEnableEsmLoader: true
+
 preferInteractive: true
 
+supportedArchitectures:
+  cpu:
+    - x64
+    - arm64
+  os:
+    - darwin
+    - linux
+    - win32
+
 telemetryUserId: yarnpkg/berry
 
 yarnPath: scripts/run-yarn.js

packages/acceptance-tests/pkg-tests-specs/sources/commands/__snapshots__/add.test.ts.snap

@@ -1,9 +1,6 @@
 import {Filename, PortablePath, ppath, xfs} from '@yarnpkg/fslib';
-
-const {
-  tests: {getPackageDirectoryPath},
-} = require(`pkg-tests-core`);
-const {parseSyml} = require(`@yarnpkg/parsers`);
+import {parseSyml}                          from '@yarnpkg/parsers';
+import {tests}                              from 'pkg-tests-core';
 
 describe(`Commands`, () => {
   describe(`add`, () => {
@@ -104,7 +101,7 @@ describe(`Commands`, () => {
     test(
       `it should add a new regular dependency to the current project (unnamed path)`,
       makeTemporaryEnv({}, async ({path, run, source}) => {
-        const packagePath = await getPackageDirectoryPath(`no-deps`, `1.0.0`);
+        const packagePath = await tests.getPackageDirectoryPath(`no-deps`, `1.0.0`);
 
         await run(`add`, packagePath);
 
@@ -570,9 +567,7 @@ describe(`Commands`, () => {
 
       expect(preUpgradeCache.find(entry => entry.includes(`no-deps-npm-1.0.0`))).toBeDefined();
 
-      const {code, stdout, stderr} = await run(`add`, `[email protected]`);
-
-      await expect({code, stdout, stderr}).toMatchSnapshot();
+      await run(`add`, `[email protected]`);
 
       const postUpgradeCache = await xfs.readdirPromise(`${path}/.yarn/cache` as PortablePath);
 
@@ -589,15 +584,14 @@ describe(`Commands`, () => {
         YARN_ENABLE_GLOBAL_CACHE: `true`,
         YARN_GLOBAL_FOLDER: `${path}/global`,
       };
+
       await run(`install`, {env});
 
       const preUpgradeCache = await xfs.readdirPromise(`${path}/global/cache` as PortablePath);
 
       expect(preUpgradeCache.find(entry => entry.includes(`no-deps-npm-1.0.0`))).toBeDefined();
 
-      const {code, stdout, stderr} = await run(`add`, `[email protected]`, {env});
-
-      await expect({code, stdout, stderr}).toMatchSnapshot();
+      await run(`add`, `[email protected]`, {env});
 
       const postUpgradeCache = await xfs.readdirPromise(`${path}/global/cache` as PortablePath);