On Windows, empty args aren't wrapped with quotes, leads to wrong argv

[alexeagle]

I add some empty args with an action, like this

args.add([], join_with=",")
args.add("hello")

On linux/mac, the program is run with
my_action '' hello
so I parse two arguments.

On windows it's run with
my_action hello

I can make a minimal repro if that's useful

[alexeagle]

Interestingly if I spill to a params file, it contains

''
hello

Which seems backwards - a blank line would have been more useful to parse args from a file, while the empty quotes would have worked in the argv

[laszlocsomor]

Yes, this is definitely a bug.

C:\tmp>type print-argv.cc
#include <iostream>

int main(int argc, char** argv) {
  std::cout << "argc=" << argc << std::endl;
  for (int i = 0; i < argc; ++i) {
    std::cout << "argv[" << i << "]=(" << argv[i] << ")" << std::endl;
  }
  return 0;
}

C:\tmp>print-argv.exe '' foo "" bar
argc=5
argv[0]=(print-argv.exe)
argv[1]=('')
argv[2]=(foo)
argv[3]=()
argv[4]=(bar)

[laszlocsomor]

...I should've added that the code is a demonstration of how empty args work on Windows.

Apparently '' is taken literally but "" means an empty string.

FYI here's an essay about cmd.exe quoting rules: https://blogs.msdn.microsoft.com/twistylittlepassagesallalike/2011/04/23/everyone-quotes-command-line-arguments-the-wrong-way/

[laszlocsomor]

/cc @meteorcloudy

[laszlocsomor]

I'm not sure about the right priority, so I'm not assigning any.

[meteorcloudy]

I'm taking a look at this.

[laszlocsomor]

Thank you Yun!

[meteorcloudy]

@alexeagle I tried to use @laszlocsomor 's print-argv.cc in a skylark rule, it seems the parameters are passed correctly.

See the following files:

execute.bzl:

def _impl(ctx):
  # The list of arguments we pass to the script.
  args = ctx.actions.args()
  args.add([], join_with=",")
  args.add("hello")
  # Action to call the script.
  ctx.actions.run(
      inputs=[],
      outputs=[ctx.outputs.out],
      arguments=[args],
      executable=ctx.executable._print_bin)

print_param = rule(
  implementation=_impl,
  attrs={
      "out": attr.output(mandatory=False),
      "_print_bin": attr.label(executable=True, cfg="host", allow_files=True,
                                default=Label("//actions_run:print"))
  }
)

and BUILD:

load(":execute.bzl", "print_param")

print_param(
    name = "run",
    out = "output.txt",
)

cc_binary(
    name = "print",
    srcs = ["print.cc"],
)

The output:

SUBCOMMAND: # //actions_run:run [action 'SkylarkAction actions_run/output.txt']
cd C:/src/tmp/_bazel_pcloudy/8oryhygq/execroot/__main__
bazel-out/host/bin/actions_run/print.exe  hello
INFO: From SkylarkAction actions_run/output.txt:
argc=3
argv[0]=(C:\src\tmp\_bazel_pcloudy\8oryhygq\execroot\__main__\bazel-out\host\bin\actions_run\print.exe)
argv[1]=()
argv[2]=(hello)

Bazel shows the command is "bazel-out/host/bin/actions_run/print.exe hello", but actually the empty argument is passed correctly because we invoke the binary through system API instead of running in terminal.

[meteorcloudy]

As I explained, this doesn't seem to be a bug in Bazel, so closing. Reopen if it's still a problem.

[alexeagle]

I can still reproduce this:

BUILD.bazel

load("@build_bazel_rules_nodejs//:defs.bzl", "nodejs_binary")

nodejs_binary(
    name = "bin",
    entry_point = "__main__/repro.js",
    data = ["repro.js"],
)

load(":index.bzl", "my_rule")
my_rule(name = "my_rule", out="params.txt")
filegroup(name = "node_modules")

WORKSPACE

git_repository(
    name = "build_bazel_rules_nodejs",
    remote = "https://github.com/bazelbuild/rules_nodejs.git",
    tag = "0.5.3")

load("@build_bazel_rules_nodejs//:defs.bzl", "node_repositories")
node_repositories(package_json = [])

index.bzl

def _my_rule(ctx):
  args = ctx.actions.args()
  args.add([], join_with=",")
  args.add("hello")
  ctx.actions.run(
      inputs=[],
      executable = ctx.executable._bin,
      outputs = [ctx.outputs.out],
      arguments = [args],
      )

my_rule = rule(_my_rule,
    attrs = {
        "out": attr.output(mandatory=False),
        "_bin": attr.label(default=Label("//:bin"),
            executable=True, cfg="host"),
    },
)

repro.js

console.error(process.argv);

bazel build :my_rule
DEBUG: C:/users/alexeagle/appdata/local/temp/_bazel_alexeagle/znpsit4n/external/bazel_tools/tools/cpp/lib_cc_configure.bzl:37:3:
Auto-Configuration Warning: 'BAZEL_VC' is not set, start looking for the latest Visual C++ installed.
DEBUG: C:/users/alexeagle/appdata/local/temp/_bazel_alexeagle/znpsit4n/external/bazel_tools/tools/cpp/lib_cc_configure.bzl:37:3:
Auto-Configuration Warning: Looking for VS%VERSION%COMNTOOLS environment variables,eg. VS140COMNTOOLS
DEBUG: C:/users/alexeagle/appdata/local/temp/_bazel_alexeagle/znpsit4n/external/bazel_tools/tools/cpp/lib_cc_configure.bzl:37:3:
Auto-Configuration Warning: Visual C++ build tools found at C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\
INFO: Analysed target //:my_rule (0 packages loaded).
INFO: Found 1 target...
INFO: From SkylarkAction params.txt:
WARNING: source-map-support module not installed.
   Stack traces from languages like TypeScript will point to generated .js files.

[ 'C:\\users\\alexeagle\\appdata\\local\\temp\\_bazel_alexeagle\\znpsit4n\\external\\nodejs\\node.exe',
  '__main__/repro.js',
  'hello' ]

Maybe it's somehow related to nodejs specifically, but if I just run the program like this, I don't see the problem:

 C:\users\alexeagle\appdata\local\temp\_bazel_alexeagle\znpsit4n\external\nodejs\node.exe repro.js '' 'hello'
[ 'C:\\users\\alexeagle\\appdata\\local\\temp\\_bazel_alexeagle\\znpsit4n\\external\\nodejs\\node.exe',
  'C:\\Users\\alexeagle\\Projects\\repro_4778\\repro.js',
  '\'\'',
  '\'hello\'' ]

[meteorcloudy]

I debugged this issue again. And found, if I modify

bazel/src/main/java/com/google/devtools/build/lib/windows/jni/WindowsProcesses.java

Lines 229 to 232 in 1f684e1

	if (arg.isEmpty()) {
	result.append("\"\"");
	continue;
	}

to

      if (arg.isEmpty()) {
        result.append("\'\'");
        continue;
      }

The nodejs example will have the expected output:

[ 'C:\\users\\pcloudy\\_bazel_pcloudy\\4isq3p4t\\external\\nodejs\\node.exe',
  '__main__/repro.js',
  '',
  'hello' ]

But the C++ example will output:

argc=3
argv[0]=(C:\users\pcloudy\_bazel_pcloudy\4isq3p4t\execroot\__main__\bazel-out\host\bin\print.exe)
argv[1]=('')
argv[2]=(hello)

The reason is different binaries have different command line parser. While the C++ binary treats "" as an empty argument, the nodejs binary just ignores it.

There is a very interesting article about this: http://daviddeley.com/autohotkey/parameters/parameters.htm

Saddly, I don't think there is any good solution from Bazel side, because Bazel doesn't know how the command line will be parsed. :(
@laszlocsomor @alexeagle

[laszlocsomor]

@meteorcloudy : thanks for looking into this issue!

What exact command line did Bazel pass to CreateProcessW in these two cases? Is there a way to pass an empty argument to a C++ binary?

[meteorcloudy]

Before the change:
<binary> "" hello
after the change:
<binary> '' hello

The first one is able to pass an empty argument to a C++ binary, but not to a nodejs binary.
The second one works for nodejs binary, but the C++ binary will receive a '' instead of an empty string.

[alexeagle]

Interesting, I also read https://blogs.msdn.microsoft.com/twistylittlepassagesallalike/2011/04/23/everyone-quotes-command-line-arguments-the-wrong-way/ which doesn't mention empty arguments but does agree that parsing the command line is up to the process.
I tried one more thing, same repro.js as above but this time calling node directly:

C:\Users\alexeagle\Projects\repro_4778                   
λ node repro.js 1 2 3 ""                                 
[ 'C:\\cmder\\bin\\node.exe',                            
  'C:\\Users\\alexeagle\\Projects\\repro_4778\\repro.js',
  '1',                                                   
  '2',                                                   
  '3',                                                   
  '' ]                                                   
                                                         
C:\Users\alexeagle\Projects\repro_4778                   
λ node repro.js 1 2 3 "" ''                              
[ 'C:\\cmder\\bin\\node.exe',                            
  'C:\\Users\\alexeagle\\Projects\\repro_4778\\repro.js',
  '1',                                                   
  '2',                                                   
  '3',                                                   
  '',                                                    
  '\'\'' ]                                               
                                                         
C:\Users\alexeagle\Projects\repro_4778                   
λ node -v                                                
v8.11.1                                                  

As you can see, the double quotes do create an empty argument. So I guess the problem is related to how we spawn the nodejs process under Bazel.

[meteorcloudy]

@alexeagle You are absolutely correct! I finally found the bug.
Because we launch the nodejs binary through a bash script, and the bash script is again launched by the native binary launcher created by Bazel. We didn't parse empty argument correctly in the native launcher, see:

bazel/src/tools/launcher/util/launcher_util.cc

Line 131 in 256c75a

wstring GetEscapedArgument(const wstring& argument, bool escape_backslash) {

After adding

  if (argument.empty()) {
    return L"\"\"";
  }

The output is now correct:

$ bazel build //:my_rule
WARNING: The following rc files are no longer being read, please transfer their contents or import their path into one of the standard rc files:
C:\Users\pcloudy/.bazelrc
DEBUG: C:/users/pcloudy/_bazel_pcloudy/4isq3p4t/external/build_bazel_rules_nodejs/internal/common/check_bazel_version.bzl:46:5:
Current Bazel is not a release version, cannot check for compatibility.
DEBUG: C:/users/pcloudy/_bazel_pcloudy/4isq3p4t/external/build_bazel_rules_nodejs/internal/common/check_bazel_version.bzl:48:5: Make sure that you are running at least Bazel 0.5.4.
INFO: Analysed target //:my_rule (0 packages loaded).
INFO: Found 1 target...
INFO: From SkylarkAction params.txt:
WARNING: source-map-support module not installed.
   Stack traces from languages like TypeScript will point to generated .js files.

[ 'C:\\users\\pcloudy\\_bazel_pcloudy\\4isq3p4t\\external\\nodejs\\node.exe',
  '__main__/repro.js',
  '',
  'hello' ]

I'll send a fix for this issue.

[alexeagle]

Awesome work again @meteorcloudy thank you!!