path-conversion: Prevent conversion of commandline flags.

[nalla]

When calling windows apps from MSYS2, the runtime tries to convert
windows style commandline flags like ´/h´ into C:/path/to/msys2/h.

If the user does not want that behavior the user can now set the the
environment variable WINSTYLE_FLAGS_ONLY when calling that command.

[kblees]

Why is this needed? Wouldn't it be simpler to stick to the documented path conversion rules [1]? I.e. write //h instead of /h for windows options?

[1] http://www.mingw.org/wiki/Posix_path_conversion

[kusma]

@kblees I use a lot of bash-scripts with long arguments myself in my daily work-flow, and having an option to disable path-conversions seems pretty convenient. But that's just my two cents.

[dscho]

Very interesting idea! I'd love to have this feature, with minor changes:

• could you enhance upon the commit message to include @kusma's use case? (I thought of that use case immediately, but let's just make sure that the commit message really drives home that point even if the reader has not encountered that problem before)
• I am not at all sure about the name WINSTYLE_FLAGS_ONLY... Maybe something more like KEEP_DOS_FLAGS? Or even simpler: SKIP_P2W?

[nalla]

Ok wait a minute. I think I know now what was my problem. I was trying to use the following switch msbuild //p:OutputPath=C:/some/path. That got me started with the idea in the first place. Thanks to @kblees hint to the mingw wiki - I got that fixed to msbuild //p:OutputPath=C:\\some\\path

[dscho]

@nalla while that is correct, it struck my as a major revelation that having the option to switch off the posix2windows mangling wholesale depending on an environment variable is just brilliant.

Now that I think of it: even in our test suite, we could benefit from this: our git blame tests really suffer from p2w mangling and our work-around is uglier than the grandfather of a blobfish. Since we do not need the p2w mangling at all when testing git blame, we could replace this work-around by a simple SKIP_P2W=1; export SKIP_P2W. 👏

Or do I miss anything?

[kblees]

I am not at all sure about the name WINSTYLE_FLAGS_ONLY... Maybe something more like KEEP_DOS_FLAGS? Or even simpler: SKIP_P2W?

Or we could just add another flag to the MSYS variable, e.g. [no]pathconv?

If we add new environment variables, they should be prefixed with MSYS_ to prevent potential clashes with other applications. And P2W would be meaningless if you don't know the MSYS sources.

[nalla]

What I can do is change the variable name to MSYS_NO_PATHCONV. As of adding another

flag to the MSYS variable, e.g. [no]pathconv

I must decline due to lack of knowledge and understanding. But If someone else would be willing to go for it - please do so 👍

[dscho]

Or we could just add another flag to the MSYS variable, e.g. [no]pathconv?

The disadvantage of this is that MSYS is interpreted at msys2-runtime startup time IIRC. With the separate environment variable handling, you should be able to switch it off while running inside a Bash (although I did not test that yet).

[dscho]

With the separate environment variable handling, you should be able to switch it off while running inside a Bash (although I did not test that yet).

Well, I just tested this. With the following echo-args.c:

#include <stdio.h>

int main(int argc, char **argv)
{
    int i;

    for (i = 0; i < argc; i++)
        fprintf(stderr, "arg %d: '%s'\n", i, argv[i]);

    return 0;
}

and a patched msys-2.0.dll:

$ echo-args /h
arg 0: 'C:\censored\echo-args.exe'
arg 1: 'H:/'

$ MSYS_NO_PATHCONV=1 echo-args /h
arg 0: 'C:\censored\echo-args.exe'
arg 1: '/h'

Sweet!!!

[dscho]

Sorry that it takes so long to release this... I encountered build problems in 32-bit mode, but I think that I'll resolve them soon.

[dscho]

Okay, finally resolved and uploaded to the Pacman repository.

[kumarharsh]

@dscho it seems like setting the MSYS_NO_PATHCONV variable to 0 is also turning off the path conversion. Is this by design?

[nalla]

@kumarharsh indeed it is. See 3a68b5b#diff-ee01d88e1ff6a07b0dc99ffc52c1e9f6R348 - The logic only checks if the variable has any value.

[kumarharsh]

OK, thanks. So setting it to $null (PS) or NUL (cmd) is the way to go.

I must really commend you guys for adding this in. It proved to be a lifesaver for me - I was writing a cross-platform Makefile which was running with the MSYS environment (but from Powershell) and I was trying to mount docker directories. It became such a mess that no matter what I tried, either MSYS was mucking up the path, or docker couldn't read it. This was the only reason I was maintaining a fork of the makefile in powershell PS1 scripts. Now, I'm just setting the environment variable when I need it:

Before:

An example of the makefile without this variable (and still didn't work because MSYS was re-translating the windows paths - also I'm relatively new to makefile so this might not be the best way to do it)

uname_S := $(shell sh -c 'uname -s 2>/dev/null || echo not')
_mkfile_path := $(abspath $(lastword $(MAKEFILE_LIST)))
_pwd := $(patsubst %/,%,$(dir $(_mkfile_path)))
ifeq ($(uname_S),Linux)  # Linux
  WORKING_DIR = $(_pwd)
endif
ifneq (,$(findstring MSYS_NT,$(uname_S)))  # Windows
    _drive := $(shell echo $(firstword $(subst :, ,$(_pwd))) | tr A-Z a-z)
    _path := $(subst \\,/,$(lastword $(subst :, ,$(_pwd))))
    WORKING_DIR := /$(_drive)$(subst :,,$(_path))
endif

.PHONY: restoredb
restoredb: ## Restore all data from a sql file to the database
                docker run -u postgres -v $(WORKING_DIR)/dumps/$(DBName)_dump.sql:/tmp/dump.sql --net host --rm postgres:9.5 psql -f /tmp/dump.sql -h localhost -U postgres $(DBName)

And the actual function in Powershell which did work:

function __getPath($path) {
  return [regex]::replace(   # First, convert the drive letter from windows style to unix style, i.e, C:\ to /c/
    $path,
    '([\w]):\\', {
      param($m)
      '/'+$m.Groups[1].Value.toLower()+'/'
    }
  ).replace('\', '/')     # Then, replace the remaining '\' to '/'
}

function make-restore {
  Param(
    [parameter(Mandatory=$true,position=0)]
    [String]
    $app
  )
  $DB_NAME = "pl_$($app)"
  $hostPath = __getPath "$($pwd)/dumps/$($DB_NAME)_dump.sql"

  docker run -u postgres --net host -v "$($hostPath):/tmp/dump.sql" --rm postgres:9.5 psql -h localhost -U postgres -f /tmp/dump.sql $DB_NAME
  echo "Restored database pl_core"
}

After I found this variable

My makefile:

.PHONY: restoredb
restoredb: export MSYS_NO_PATHCONV=1 # stop path conversion for msys in windows
restoredb: ## Restore all data from a sql file to the database
                docker run -u postgres -v `pwd`/dumps/$(DBName)_dump.sql:/tmp/dump.sql --net host --rm postgres:9.5 psql -f /tmp/dump.sql -h localhost -U postgres $(DBName)