fs: use w flag for writeFileSync with utf8 encoding when flag not specified

[MuriloKakazu]

PR #49884 seems to have accidentally changed the behavior for fs.writeFileSync with utf-8 encoding when the file does not exist, as compared to previous node versions.

On a low level, it seems we are not passing the O_CREAT flag to uvlib anymore.

Examples:

In node 16.16.0: ✅

❯ nvm use 16.16
Now using node v16.16.0 (npm v8.11.0)
❯ node
Welcome to Node.js v16.16.0.
Type ".help" for more information.
> fs.writeFileSync('./test.txt', 'test', {encoding: 'utf8'});
undefined
> fs.readFileSync('./test.txt');
<Buffer 74 65 73 74>

In node 21.2.0: ✅

❯ nvm use 21.2
Now using node v21.2.0 (npm v10.2.3)
❯ node
Welcome to Node.js v21.2.0.
Type ".help" for more information.
> fs.writeFileSync('./test.txt', 'test', {encoding: 'utf8'});
undefined
> fs.readFileSync('./test.txt');
<Buffer 74 65 73 74>

In node 21.3.0 (currently latest): ❌

❯ nvm use 21.3
Now using node v21.3.0 (npm v10.2.4)
❯ node
Welcome to Node.js v21.3.0.
Type ".help" for more information.
> fs.writeFileSync('./test.txt', 'test', {encoding: 'utf8'});
Uncaught Error: ENOENT: no such file or directory, open './test.txt'
    at Object.writeFileSync (node:fs:2352:20) {
  errno: -2,
  code: 'ENOENT',
  syscall: 'open',
  path: './test.txt'
}

Currently, a workaround for 21.3.0 is to pass the w flag (which includes O_CREAT) explicitly when calling writeFileSync. e.g:

fs.writeFileSync('./test.txt', 'test', {encoding: 'utf8', flag: 'w'}); --> works
fs.writeFileSync('./test.txt', 'test', {encoding: 'utf8'}); --> does not work

This PR will just set the w flag back as the default value when it is not specified, so its the same behavior from previous node versions.

Fixes #50989

[anonrig]

Can you add a test?

[MuriloKakazu]

@anonrig Done :)

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/56038/

[chenrui333]

Works for me. Thanks for the quick turnaround!

Homebrew/homebrew-core#156024

[bricss]

It would be great to get this fixed asap with semver patch release at least 👮

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/56046/

[nodejs-github-bot]

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----------------------------------- PR info ------------------------------------
Title      fs: use w flag for writeFileSync with utf8 encoding when flag not specified (#50990)
Author     Murilo Kakazu  (@MuriloKakazu, first-time contributor)
Branch     MuriloKakazu:fix/default-flag-fs-write-file-sync -> nodejs:main
Labels     fs, author ready, needs-ci
Commits    2
 - fs: use default w flag for writeFileSync with utf8 encoding
 - fs: add tests for writeFileSync with no flag
Committers 1
 - Murilo Kakazu 
PR-URL: https://github.com/nodejs/node/pull/50990
Reviewed-By: Luigi Pinca 
Reviewed-By: Yagiz Nizipli 
------------------------------ Generated metadata ------------------------------
PR-URL: https://github.com/nodejs/node/pull/50990
Reviewed-By: Luigi Pinca 
Reviewed-By: Yagiz Nizipli 
--------------------------------------------------------------------------------
   ℹ  This PR was created on Fri, 01 Dec 2023 07:05:02 GMT
   ✔  Approvals: 2
   ✔  - Luigi Pinca (@lpinca): https://github.com/nodejs/node/pull/50990#pullrequestreview-1760486535
   ✔  - Yagiz Nizipli (@anonrig) (TSC): https://github.com/nodejs/node/pull/50990#pullrequestreview-1760934016
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--------------------------------------------------------------------------------
Auto-merging lib/fs.js
[main 2fba1f3a18] fs: use default w flag for writeFileSync with utf8 encoding
 Author: Murilo Kakazu 
 Date: Fri Dec 1 03:45:10 2023 -0300
 1 file changed, 3 insertions(+), 3 deletions(-)
[main 934e830937] fs: add tests for writeFileSync with no flag
 Author: Murilo Kakazu 
 Date: Fri Dec 1 13:46:14 2023 -0300
 1 file changed, 16 insertions(+)
   ✔  Patches applied
There are 2 commits in the PR. Attempting autorebase.
Rebasing (2/4)
Executing: git node land --amend --yes

--------------------------------- New Message ----------------------------------

fs: use default w flag for writeFileSync with utf8 encoding
PR-URL: #50990

Reviewed-By: Luigi Pinca luigipinca@gmail.com

Reviewed-By: Yagiz Nizipli yagiz.nizipli@sentry.io
[detached HEAD 7d6cf7982e] fs: use default w flag for writeFileSync with utf8 encoding

Author: Murilo Kakazu yuri.kakazu@gmail.com

Date: Fri Dec 1 03:45:10 2023 -0300

1 file changed, 3 insertions(+), 3 deletions(-)

Rebasing (3/4)

Rebasing (4/4)
Executing: git node land --amend --yes

--------------------------------- New Message ----------------------------------

fs: add tests for writeFileSync with no flag
PR-URL: #50990

Reviewed-By: Luigi Pinca luigipinca@gmail.com

Reviewed-By: Yagiz Nizipli yagiz.nizipli@sentry.io
[detached HEAD 5220933a12] fs: add tests for writeFileSync with no flag

Author: Murilo Kakazu yuri.kakazu@gmail.com

Date: Fri Dec 1 13:46:14 2023 -0300

1 file changed, 16 insertions(+)
Successfully rebased and updated refs/heads/main.
ℹ  Add commit-queue-squash label to land the PR as one commit, or commit-queue-rebase to land as separate commits.

https://github.com/nodejs/node/actions/runs/7075388656

[nodejs-github-bot]

Landed in 7bfb087