Hi, I saw this is a good first issue, so I want to try fixing this issue. How should I go about doing this ?
I tried reading aquery_differ.py but I can't figure out where's the issue.

@keith could you please provide a minimal way to reproduce the issue?

In a tiny project with an empty WORKSPACE and:

# BUILD
cc_library(
    name = "foo",
    srcs = ["foo.c"],
)

# foo.c
void foo() {}

run:

bazel aquery foo --output=proto > /tmp/noenv.proto
bazel aquery --action_env=FOO=BAR foo --output=proto > /tmp/env.proto

Then in a bazel checkout run:

bazel run //tools/aquery_differ -- --before=/tmp/noenv.proto --after=/tmp/env.proto

In this case no difference is produced. But using -s you can see these differ with the env var:

$ bazel build foo -s
INFO: Analyzed target //:foo (3 packages loaded, 146 targets configured).
INFO: Found 1 target...
SUBCOMMAND: # //:foo [action 'Compiling foo.c', configuration: 63cc040ed2b86a512099924e698df6e0b9848625e6ca33d9556c5993dccbc2fb, execution platform: @local_config_platform//:host]
(cd /private/var/tmp/_bazel_ksmiley/1fb2af3fe9ab063484352bf1778d83fa/execroot/__main__ && \
  exec env - \
    APPLE_SDK_PLATFORM=MacOSX \
    APPLE_SDK_VERSION_OVERRIDE=11.0 \
    PATH=/Users/ksmiley/Library/Caches/bazelisk/downloads/bazelbuild/bazel-3.7.0-darwin-x86_64/bin:.git/safe/../../.build/debug:/Users/ksmiley/.gem/bin:/Users/ksmiley/.pyenv/shims:/Users/ksmiley/.pyenv/bin:/Users/ksmiley/go/bin:/usr/local/opt/make/libexec/gnubin:/usr/local/opt/gnu-tar/libexec/gnubin:/usr/local/opt/gnu-sed/libexec/gnubin:/usr/local/opt/findutils/libexec/gnubin:/usr/local/opt/coreutils/libexec/gnubin:/Users/ksmiley/Library/Android/sdk/tools:/Users/ksmiley/Library/Android/sdk/platform-tools:/Users/ksmiley/.lyftkube-bin:/Users/ksmiley/dev/lyft/k8stools:/Users/ksmiley/dev/arcanist/bin:/Users/ksmiley/.bin:/Users/ksmiley/.local/bin:/usr/local/bin:/usr/local/sbin:/usr/bin:/usr/sbin:/bin:/sbin \
    XCODE_VERSION_OVERRIDE=12.2.0.12B45b \
  external/local_config_cc/wrapped_clang '-D_FORTIFY_SOURCE=1' -fstack-protector -fcolor-diagnostics -Wall -Wthread-safety -Wself-assign -fno-omit-frame-pointer -O0 -DDEBUG -iquote . -iquote bazel-out/darwin-fastbuild/bin -MD -MF bazel-out/darwin-fastbuild/bin/_objs/foo/foo.d '-frandom-seed=bazel-out/darwin-fastbuild/bin/_objs/foo/foo.o' -isysroot __BAZEL_XCODE_SDKROOT__ -F__BAZEL_XCODE_SDKROOT__/System/Library/Frameworks -F__BAZEL_XCODE_DEVELOPER_DIR__/Platforms/MacOSX.platform/Developer/Library/Frameworks '-mmacosx-version-min=11.0' -no-canonical-prefixes -Wno-builtin-macro-redefined '-D__DATE__="redacted"' '-D__TIMESTAMP__="redacted"' '-D__TIME__="redacted"' -c foo.c -o bazel-out/darwin-fastbuild/bin/_objs/foo/foo.o)
Target //:foo up-to-date:
  bazel-bin/libfoo.a
  bazel-bin/libfoo.so
INFO: Elapsed time: 0.371s, Critical Path: 0.12s
INFO: 2 processes: 1 internal, 1 darwin-sandbox.
INFO: Build completed successfully, 2 total actions

$ bazel build foo -s --action_env=FOO=BAR
INFO: Analyzed target //:foo (3 packages loaded, 146 targets configured).
INFO: Found 1 target...
SUBCOMMAND: # //:foo [action 'Compiling foo.c', configuration: e68fb7c6d21d5b0d038e004ffd72b846caf21f744afb32b4726a6b396a76b67e, execution platform: @local_config_platform//:host]
(cd /private/var/tmp/_bazel_ksmiley/1fb2af3fe9ab063484352bf1778d83fa/execroot/__main__ && \
  exec env - \
    APPLE_SDK_PLATFORM=MacOSX \
    APPLE_SDK_VERSION_OVERRIDE=11.0 \
    FOO=BAR \
    PATH=/Users/ksmiley/Library/Caches/bazelisk/downloads/bazelbuild/bazel-3.7.0-darwin-x86_64/bin:.git/safe/../../.build/debug:/Users/ksmiley/.gem/bin:/Users/ksmiley/.pyenv/shims:/Users/ksmiley/.pyenv/bin:/Users/ksmiley/go/bin:/usr/local/opt/make/libexec/gnubin:/usr/local/opt/gnu-tar/libexec/gnubin:/usr/local/opt/gnu-sed/libexec/gnubin:/usr/local/opt/findutils/libexec/gnubin:/usr/local/opt/coreutils/libexec/gnubin:/Users/ksmiley/Library/Android/sdk/tools:/Users/ksmiley/Library/Android/sdk/platform-tools:/Users/ksmiley/.lyftkube-bin:/Users/ksmiley/dev/lyft/k8stools:/Users/ksmiley/dev/arcanist/bin:/Users/ksmiley/.bin:/Users/ksmiley/.local/bin:/usr/local/bin:/usr/local/sbin:/usr/bin:/usr/sbin:/bin:/sbin \
    XCODE_VERSION_OVERRIDE=12.2.0.12B45b \
  external/local_config_cc/wrapped_clang '-D_FORTIFY_SOURCE=1' -fstack-protector -fcolor-diagnostics -Wall -Wthread-safety -Wself-assign -fno-omit-frame-pointer -O0 -DDEBUG -iquote . -iquote bazel-out/darwin-fastbuild/bin -MD -MF bazel-out/darwin-fastbuild/bin/_objs/foo/foo.d '-frandom-seed=bazel-out/darwin-fastbuild/bin/_objs/foo/foo.o' -isysroot __BAZEL_XCODE_SDKROOT__ -F__BAZEL_XCODE_SDKROOT__/System/Library/Frameworks -F__BAZEL_XCODE_DEVELOPER_DIR__/Platforms/MacOSX.platform/Developer/Library/Frameworks '-mmacosx-version-min=11.0' -no-canonical-prefixes -Wno-builtin-macro-redefined '-D__DATE__="redacted"' '-D__TIMESTAMP__="redacted"' '-D__TIME__="redacted"' -c foo.c -o bazel-out/darwin-fastbuild/bin/_objs/foo/foo.o)
Target //:foo up-to-date:
  bazel-bin/libfoo.a
  bazel-bin/libfoo.so
INFO: Elapsed time: 0.387s, Critical Path: 0.12s
INFO: 2 processes: 1 internal, 1 darwin-sandbox.
INFO: Build completed successfully, 2 total actions