GODEBUG='winsymlink=0' should only be set on windoze

[randomizedcoder]

G'day,

Rules_go does a good job a making the environment hermetic, by carefully defining which environment variables make it to the sandbox.

However, "GODEBUG='winsymlink=0'" should only be set for Windoze builds.

The bug is on this line, which always includes this option.
https://github.com/bazel-contrib/rules_go/blob/master/go/private/context.bzl#L552

Probably this option should only be included when "mode.goos" == Windoze

Run this command to start an interactive shell in an identical sandboxed environment:
(exec env - \
    CC=external/toolchains_llvm++llvm+llvm_toolchain/bin/cc_wrapper.sh \
    CGO_ENABLED=1 \
    GOARCH=amd64 \
    GODEBUG='winsymlink=0' \                                 <----- should only be set on windoze
    GOEXPERIMENT=nocoverageredesign \
    GOOS=linux \
    GOPATH='' \
    GOROOT=bazel-out/k8-fastbuild/bin/external/rules_go+/stdlib_ \
    GOROOT_FINAL=GOROOT \
    GOTOOLCHAIN=local \
    PATH=external/toolchains_llvm++llvm+llvm_toolchain/bin:/bin:/usr/bin \
    TMPDIR=/tmp \
    ZERO_AR_DATE=1 \
  /home/das/.cache/bazel/_bazel_das/install/254cc618fc52f01b2b1d5fd6ff343774/linux-sandbox -t 15 -w /dev/shm -w /home/das/.cache/bazel/_bazel_das/2069c7e7bbea1cec17d73a6b1498e560/sandbox/linux-sandbox/13/execroot/_main -w /tmp -M /home/das/.cache/bazel/_bazel_das/2069c7e7bbea1cec17d73a6b1498e560/sandbox/linux-sandbox/13/_hermetic_tmp -m /tmp -S /home/das/.cache/bazel/_bazel_das/2069c7e7bbea1cec17d73a6b1498e560/sandbox/linux-sandbox/13/stats.out -D /home/das/.cache/bazel/_bazel_das/2069c7e7bbea1cec17d73a6b1498e560/sandbox/linux-sandbox/13/debug.out -- /bin/sh -i)
ERROR: /home/das/Downloads/go_hello_world_race/BUILD.bazel:24:11: GoCompilePkg hello_lib.a failed: (Exit 1): linux-sandbox failed: error executing GoCompilePkg command 
  (cd /home/das/.cache/bazel/_bazel_das/2069c7e7bbea1cec17d73a6b1498e560/sandbox/linux-sandbox/13/execroot/_main && \
  exec env - \
    CC=external/toolchains_llvm++llvm+llvm_toolchain/bin/cc_wrapper.sh \
    CGO_ENABLED=1 \
    GOARCH=amd64 \
    GODEBUG='winsymlink=0' \ <---- :(
    GOEXPERIMENT=nocoverageredesign \           
    GOOS=linux \
    GOPATH='' \
    GOROOT=bazel-out/k8-fastbuild/bin/external/rules_go+/stdlib_ \
    GOROOT_FINAL=GOROOT \
    GOTOOLCHAIN=local \
    PATH=external/toolchains_llvm++llvm+llvm_toolchain/bin:/bin:/usr/bin \
    TMPDIR=/tmp \
    ZERO_AR_DATE=1 \
  /home/das/.cache/bazel/_bazel_das/install/254cc618fc52f01b2b1d5fd6ff343774/linux-sandbox -t 15 -w /dev/shm -w 

I think this bug was introduced by #4050 when trying to resolve
#4049

You can definitely argue this doesn't matter because it's ignored on non-Windoze, however I bet you would reject an PR if somebody wanted to set "FOO=BAR", because it would be unnecessarily cluttering the environment variable space.

Thanks,
Dave

[randomizedcoder]

In another part of rules_go, the pattern for "windows" is:

    if sdk.goos == "windows":
        # Using pre-declared directory for temporary output as there is no safe
        # way under Windows to create unique temporary dir.
        gotmp = ctx.actions.declare_directory("gotmp")
        cmd = """@echo off

https://github.com/bazel-contrib/rules_go/blob/393faea31d43012fbb7887dfbddb869cb5cf58f5/go/private/rules/binary.bzl#L488C1-L492C27