RFR: JDK-8266396: Add VSCMD_DEBUG for solving WINSDK_DIR build error

[John Neffenger]

On Fri, 7 May 2021 13:42:49 GMT, Kevin Rushforth <kcr at openjdk.org> wrote:

> It would be more convenient to ask the developer set `VSCMD_DEBUG` via an env variable, rather than asking them to edit `win.gradle`.

Thanks, Kevin. That is the most direct approach. I didn't document it that way for the following reasons:

1. Using the `export` command under Cygwin sets the variable for the *entire* build. In the current commit, the variable, when defined, is set only for the duration of the `genVSproperties.bat` batch file and the batch files it calls.
2. I would like to see this documented in the code, even if just as comments, as opposed to the Wiki. When I got the error, the first thing I did was search through the code base for `WINSDK_DIR`. I would have found the lines added by this pull request right away.

Don't let the name confused you. The variable is not a debugging variable; it doesn't enable debug trace logging. What it actually does is prevent the batch files from sending both standard output and standard error to "NUL", which they do by default. Defining it with `VSCMD_DEBUG=3` really means, "Please don't silently discard really important error messages!" You don't expect all error messages to be hidden from you when you invoke 3,985 Windows batch file statements, but that's exactly what's happening now:


$ cloc trace.bat
       1 text file.
       1 unique file.                              
       0 files ignored.

github.com/AlDanial/cloc v 1.82  T=0.01 s (73.6 files/s, 438775.4 lines/s)
-------------------------------------------------------------------------------
Language                     files          blank        comment           code
-------------------------------------------------------------------------------
DOS Batch                        1           1938             40           3985
-------------------------------------------------------------------------------


I'll up the ante and suggest that we set the value to "3" by default in the build file (and disable telemetry). Then the batch files will behave as one would expect. I tested all values of the variable (undefined, valid, and invalid), and the generated file `windows_tools.properties` was identical in all cases.

Otherwise, where do you suggest we document this? If you disfavor the current options ("" and "3"), what do you think of making it three comment lines in the `win.gradle` file?

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PR: https://git.openjdk.java.net/jfx/pull/488