Using --stdin (without --stdout) sometimes does not cause formatted output to go to stdout

[emdash-ie]

• latest version of CLI and latest version in .scalafmt.conf

Configuration (required)

Please paste the contents of your .scalafmt.conf file here:

version = 3.7.14
runner.dialect=scala213

maxColumn = 120
trailingCommas = always
align.preset = none
fileOverride {
  "glob:**/support-internationalisation/src/test/scala/**" {
     runner.dialect = scala3
  }
  "glob:**/support-internationalisation/src/main/scala/**" {
     runner.dialect = scala3
  }
}

Steps

Given Something.scala:

class Something() {
  def something() = {}
}

Running scalafmt --debug Something.scala produces this output and the file does not change (as expected):

Using core runner [3.7.14]
Working directory: /Users/emily_bourke/code/support-frontend/support-frontend/app/utils
parsed config (v3.7.14)
Files to be formatted:
/Users/emily_bourke/code/support-frontend/support-frontend/app/utils/Something.scala

Running scalafmt --debug --stdout Something.scala produces this output and the file does not change (as expected):

Using core runner [3.7.14]
Working directory: /Users/emily_bourke/code/support-frontend/support-frontend/app/utils
parsed config (v3.7.14)
Files to be formatted:
/Users/emily_bourke/code/support-frontend/support-frontend/app/utils/Something.scala
class Something() {
  def something() = {}
}

Running cat Something.scala | scalafmt --debug --stdin --stdout produces this output and the file does not change (as expected):

Using core runner [3.7.14]
Working directory: /Users/emily_bourke/code/support-frontend/support-frontend/app/utils
parsed config (v3.7.14)
class Something() {
  def something() = {}
}

Based on the help documentation (which says scalafmt --stdin # read from stdin and print to stdout) I would expect removing --stdout to make no difference, but running cat Something.scala | scalafmt --debug --stdin produces the following output and the file does not change.

Using core runner [3.7.14]
Working directory: /Users/emily_bourke/code/support-frontend/support-frontend/app/utils
parsed config (v3.7.14)

Why is the file not output onto stdout in this case? (This happens when the file is correctly formatted, and mostly doesn’t happen (or never happens – not sure) if the file needs formatting.)

Workaround

I can add the --stdout flag (and raise a PR to do that in format-all-mode).

Notes

• I’m using fish as my shell
• I came across this problem while using format-all-mode in Doom Emacs
• Explanation and documentation of this behaviour would be acceptable to me instead of changing it

[kitbellew]

--stdin does not imply --stdout. the help needs to be adjusted.

[emdash-ie]

--stdin does not imply --stdout. the help needs to be adjusted.

Perfect, thanks for clarifying :)