Fix build options for non transitive load for bazel 0.25

[jinmel]

bazelbuild/bazel#5636

[g-easy]

Both with and without this change I'm seeing:

opencensus-cpp/opencensus/copts.bzl:24:1: file '@com_google_absl//absl:copts/configure_copts.bzl' does not contain symbol 'ABSL_GCC_FLAGS'

[jinmel]

@g-easy absl-cpp also needs an update.

abseil/abseil-cpp#301

[g-easy]

Ahh ok, I was trying it against abseil at HEAD.

Alternatively: should we just consume ABSL_DEFAULT_COPTS which is defined in absl/copts/configure_copts.bzl?

[jinmel]

@g-easy consuming DEFAULT_COPTS directly seems better :)

btw, should I keep my commit to single commit per merge request? or is it squashed into one commit when I merge it. Just curious how it works in github

[g-easy]

It all gets squashed so feel free to push as many commits as you'd like. :D

Also I try to clean up the final commit message / set it to the topic + initial comment.

[g-easy]

How about:

DEFAULT_COPTS = select({
    "//opencensus:llvm_compiler": ABSL_DEFAULT_COPTS + WERROR,
    "//opencensus:windows": ABSL_DEFAULT_COPTS, # Without the gcc/clang specific WERROR
    "etc

[jinmel]

It seems like select within select isn't possible

ERROR: /Users/jinsuk/Code/opencensus-cpp/opencensus/context/BUILD:24:1: //opencensus/context:context: expected value of type 'list(string)' for each branch in select expression of attribute 'copts' in 'cc_library' rule (including '//opencensus:llvm_compiler'), but got select({"//absl:windows": ["/W3", "/DNOMINMAX", "/DWIN32_LEAN_AND_MEAN", "/D_CRT_SECURE_NO_WARNINGS", "/D_SCL_SECURE_NO_WARNINGS", "/D_ENABLE_EXTENDED_ALIGNED_STORAGE", "/wd4005", "/wd4068", "/wd4180", "/wd4244", "/wd4267", "/wd4503", "/wd4800"], "//absl:llvm_compiler": ["-Wall", "-Wextra", "-Weverything", "-Wno-c++98-compat-pedantic", "-Wno-conversion", "-Wno-covered-switch-default", "-Wno-deprecated", "-Wno-disabled-macro-expansion", "-Wno-double-promotion", "-Wno-comma", "-Wno-extra-semi", "-Wno-extra-semi-stmt", "-Wno-packed", "-Wno-padded", "-Wno-sign-compare", "-Wno-float-conversion", "-Wno-float-equal", "-Wno-format-nonliteral", "-Wno-gcc-compat", "-Wno-global-constructors", "-Wno-exit-time-destructors", "-Wno-nested-anon-types", "-Wno-non-modular-include-in-module", "-Wno-old-style-cast", "-Wno-range-loop-analysis", "-Wno-reserved-id-macro", "-Wno-shorten-64-to-32", "-Wno-switch-enum", "-Wno-thread-safety-negative", "-Wno-unknown-warning-option", "-Wno-unreachable-code", "-Wno-unused-macros", "-Wno-weak-vtables", "-Wbitfield-enum-conversion", "-Wbool-conversion", "-Wconstant-conversion", "-Wenum-conversion", "-Wint-conversion", "-Wliteral-conversion", "-Wnon-literal-null-conversion", "-Wnull-conversion", "-Wobjc-literal-conversion", "-Wno-sign-conversion", "-Wstring-conversion"], "//conditions:default": ["-Wall", "-Wextra", "-Wcast-qual", "-Wconversion-null", "-Wmissing-declarations", "-Woverlength-strings", "-Wpointer-arith", "-Wunused-local-typedefs", "-Wunused-result", "-Wvarargs", "-Wvla", "-Wwrite-strings", "-Wno-missing-field-initializers", "-Wno-sign-compare"]}) + ["-Werror=return-type", "-Werror=switch"] (select)

[jinmel]

@g-easy
https://github.com/abseil/abseil-cpp/blob/aa468ad75539619b47979911297efbb629c52e44/absl/copts/configure_copts.bzl#L30

It seems like using ABSL_DEFAULT_COPTS causes error because it queries //absl:windows of which 'absl' package is not found in opencensus-cpp directory :(

[g-easy]

select within select isn't possible
I didn't know this. It's unfortunate but unsurprising.

How about:

DEFAULT_COPTS = ABSL_DEFAULT_COPS + WARN_OPTS

Where:

WARN_OPTS = select(...

Would that work?

[jinmel]

is this what you meant?
I think the select causing error is within ABSL_DEFAULT_COPTS.. I wonder if this variable is usable anywhere

[jinmel]

There still needs to be an update in abseil-cpp side.

[jinmel]

Just addressed your comment

[g-easy]

IMO let's do a minimal build fix for now, which is this:

 load(
-    "@com_google_absl//absl:copts/configure_copts.bzl",
+    "@com_google_absl//absl:copts/GENERATED_copts.bzl",

Longer term we should probably depend on ABSL_DEFAULT_COPTS from configure_copts.bzl but it looks like there's an error in how bazel handles select() across external repositories.

Another possible later solution is for opencensus-cpp to maintain its own set of flags. We initially went with Abseil's because we use the same style guide (which results in a lots of sign conversion warnings).

Could you please make your PR just change that load()?

[jinmel]

abseil/abseil-cpp#301 (comment)

It seems like those ABSL_LLVM* kind of flags weren't meant to be exported.

They instruct us to use ABSL_DEFAULT_COPTS which isn't usable :D

[g-easy]

I'm working on fixing the format.sh problem. :)