go_binary, go_test: add gotags attribute

The gotags attribute sets which build tags are enabled when evaluting
build constraints. This is equivalent to setting
--@io_bazel_rules_go//go/config:tags on the command line.

Fixes bazel-contrib#1351

go/core.rst

@@ -522,14 +522,19 @@ Attributes
 | This is one of the `mode attributes`_ that controls whether to instrument                        |
 | code for data race detection. It may be :value:`on`, :value:`off`, or                            |
 | :value:`auto`. In most cases, it's better to enable race detection globally                      |
-| with ``--features=race`` on the command line.                                                    |
+| with ``--@io_bazel_rules_go//go/config:race`` on the command line.                               |
 +----------------------------+-----------------------------+---------------------------------------+
 | :param:`msan`              | :type:`string`              | :value:`auto`                         |
 +----------------------------+-----------------------------+---------------------------------------+
 | This is one of the `mode attributes`_ that controls whether to instrument                        |
 | code for memory santization. It may be :value:`on`, :value:`off`, or                             |
 | :value:`auto`. In most cases, it's better to enable memory sanitization                          |
-| globally with ``--features=msan`` on the command line.                                           |
+| globally with ``--@io_bazel_rules_go//go/config:msan`` on the command line.                      |
++----------------------------+-----------------------------+---------------------------------------+
+| :param:`gotags`            | :type:`string_list`         : :value:`[]`                           |
++----------------------------+-----------------------------+---------------------------------------+
+| This is one of the `mode attributes`_ that controls which build tags are                         |
+| enabled when evaluating build constraints. Useful for conditional compilation.                   |
 +----------------------------+-----------------------------+---------------------------------------+
 | :param:`goos`              | :type:`string`              | :value:`auto`                         |
 +----------------------------+-----------------------------+---------------------------------------+
@@ -733,14 +738,19 @@ Attributes
 | This is one of the `mode attributes`_ that controls whether to instrument                        |
 | code for data race detection. It may be :value:`on`, :value:`off`, or                            |
 | :value:`auto`. In most cases, it's better to enable race detection globally                      |
-| with ``--features=race`` on the command line.                                                    |
+| with ``--@io_bazel_rules_go//go/config:race`` on the command line.                               |
 +----------------------------+-----------------------------+---------------------------------------+
 | :param:`msan`              | :type:`string`              | :value:`auto`                         |
 +----------------------------+-----------------------------+---------------------------------------+
 | This is one of the `mode attributes`_ that controls whether to instrument                        |
 | code for memory santization. It may be :value:`on`, :value:`off`, or                             |
 | :value:`auto`. In most cases, it's better to enable memory sanitization                          |
-| globally with ``--features=msan`` on the command line.                                           |
+| globally with ``--@io_bazel_rules_go//go/config:msan`` on the command line.                      |
++----------------------------+-----------------------------+---------------------------------------+
+| :param:`gotags`            | :type:`string_list`         : :value:`[]`                           |
++----------------------------+-----------------------------+---------------------------------------+
+| This is one of the `mode attributes`_ that controls which build tags are                         |
+| enabled when evaluating build constraints. Useful for conditional compilation.                   |
 +----------------------------+-----------------------------+---------------------------------------+
 | :param:`goos`              | :type:`string`              | :value:`auto`                         |
 +----------------------------+-----------------------------+---------------------------------------+

go/modes.rst

@@ -46,46 +46,51 @@ or using `Bazel configuration transitions`_.
 
 +-------------------+----------------+-----------------------------------------+
 | **Name**          | **Type**       | **Default value**                       |
-+-------------------+----------------+-----------------------------------------+
-| :param:`static`   | :type:`bool`   | :value:`false`                          |
-+-------------------+----------------+-----------------------------------------+
++-------------------+---------------------+------------------------------------+
+| :param:`static`   | :type:`bool`        | :value:`false`                     |
++-------------------+---------------------+------------------------------------+
 | Statically links the target binary. May not always work since parts of the   |
 | standard library and other C dependencies won't tolerate static linking.     |
 | Works best with ``pure`` set as well.                                        |
-+-------------------+----------------+-----------------------------------------+
-| :param:`race`     | :type:`bool`   | :value:`false`                          |
-+-------------------+----------------+-----------------------------------------+
++-------------------+---------------------+------------------------------------+
+| :param:`race`     | :type:`bool`        | :value:`false`                     |
++-------------------+---------------------+------------------------------------+
 | Instruments the binary for race detection. Programs will panic when a data   |
 | race is detected. Requires cgo. Mutually exclusive with ``msan``.            |
-+-------------------+----------------+-----------------------------------------+
-| :param:`msan`     | :type:`bool`   | :value:`false`                          |
-+-------------------+----------------+-----------------------------------------+
++-------------------+---------------------+------------------------------------+
+| :param:`msan`     | :type:`bool`        | :value:`false`                     |
++-------------------+---------------------+------------------------------------+
 | Instruments the binary for memory sanitization. Requires cgo. Mutually       |
 | exclusive with ``race``.                                                     |
-+-------------------+----------------+-----------------------------------------+
-| :param:`pure`     | :type:`bool`   | :value:`false`                          |
-+-------------------+----------------+-----------------------------------------+
++-------------------+---------------------+------------------------------------+
+| :param:`pure`     | :type:`bool`        | :value:`false`                     |
++-------------------+---------------------+------------------------------------+
 | Disables cgo, even when a C/C++ toolchain is configured (similar to setting  |
 | ``CGO_ENABLED=0``). Packages that contain cgo code may still be built, but   |
 | the cgo code will be filtered out, and the ``cgo`` build tag will be false.  |
-+-------------------+----------------+-----------------------------------------+
-| :param:`strip`    | :type:`bool`   | :value:`false`                          |
-+-------------------+----------------+-----------------------------------------+
++-------------------+---------------------+------------------------------------+
+| :param:`strip`    | :type:`bool`        | :value:`false`                     |
++-------------------+---------------------+------------------------------------+
 | Strips symbols from compiled packages and linked binaries (using the ``-w``  |
 | flag). May also be set with the ``--strip`` command line option, which       |
 | affects C/C++ targets, too.                                                  |
-+-------------------+----------------+-----------------------------------------+
-| :param:`debug`    | :type:`bool`   | :value:`false`                          |
-+-------------------+----------------+-----------------------------------------+
++-------------------+---------------------+------------------------------------+
+| :param:`debug`    | :type:`bool`        | :value:`false`                     |
++-------------------+---------------------+------------------------------------+
 | Includes debugging information in compiled packages (using the ``-N`` and    |
 | ``-l`` flags).                                                               |
-+-------------------+----------------+-----------------------------------------+
-| :param:`linkmode` | :type:`string` | :value:`"normal"`                       |
-+-------------------+----------------+-----------------------------------------+
++-------------------+---------------------+------------------------------------+
+| :param:`gotags`   | :type:`string_list` | :value:`[]`                        |
++-------------------+---------------------+------------------------------------+
+| Controls which build tags are enabled when evaluating build constraints in   |
+| source files. Useful for conditional compilation.                            |
++-------------------+---------------------+------------------------------------+
+| :param:`linkmode` | :type:`string`      | :value:`"normal"`                  |
++-------------------+---------------------+------------------------------------+
 | Determines how the Go binary is built and linked. Similar to ``-buildmode``. |
 | Must be one of ``"normal"``, ``"shared"``, ``"pie"``, ``"plugin"``,          |
 | ``"c-shared"``, ``"c-archive"``.                                             |
-+-------------------+----------------+-----------------------------------------+
++-------------------+---------------------+------------------------------------+
 
 Platforms
 ---------

go/private/rules/transition.bzl

@@ -54,7 +54,7 @@ def go_transition_wrapper(kind, transition_kind, name, **kwargs):
     regular rule. This prevents targets from being rebuilt for an alternative
     configuration identical to the default configuration.
     """
-    transition_keys = ("goos", "goarch", "pure", "static", "msan", "race", "linkmode")
+    transition_keys = ("goos", "goarch", "pure", "static", "msan", "race", "gotags", "linkmode")
     need_transition = any([key in kwargs for key in transition_keys])
     if need_transition:
         transition_kind(name = name, **kwargs)
@@ -89,6 +89,7 @@ def go_transition_rule(**kwargs):
             default = "auto",
             values = ["auto", "on", "off"],
         ),
+        "gotags": attr.string_list(default = []),
         "linkmode": attr.string(
             default = "auto",
             values = ["auto"] + LINKMODES,
@@ -126,6 +127,11 @@ def _go_transition_impl(settings, attr):
     _set_ternary(settings, attr, "race")
     _set_ternary(settings, attr, "msan")
 
+    tags = getattr(attr, "gotags", [])
+    if tags:
+        tags_label = _filter_transition_label("@io_bazel_rules_go//go/config:tags")
+        settings[tags_label] = tags
+
     linkmode = getattr(attr, "linkmode", "auto")
     if linkmode != "auto":
         if linkmode not in LINKMODES:
@@ -143,6 +149,7 @@ go_transition = transition(
         "@io_bazel_rules_go//go/config:msan",
         "@io_bazel_rules_go//go/config:race",
         "@io_bazel_rules_go//go/config:pure",
+        "@io_bazel_rules_go//go/config:tags",
         "@io_bazel_rules_go//go/config:linkmode",
     ]],
     outputs = [_filter_transition_label(label) for label in [
@@ -151,6 +158,7 @@ go_transition = transition(
         "@io_bazel_rules_go//go/config:msan",
         "@io_bazel_rules_go//go/config:race",
         "@io_bazel_rules_go//go/config:pure",
+        "@io_bazel_rules_go//go/config:tags",
         "@io_bazel_rules_go//go/config:linkmode",
     ]],
 )

tests/core/go_binary/BUILD.bazel

@@ -144,3 +144,22 @@ go_binary(
     static = "on",
     tags = ["manual"],
 )
+
+go_binary(
+    name = "tags_bin",
+    srcs = [
+        "tags_main_bad.go",
+        "tags_main_good.go",
+    ],
+    gotags = ["good"],
+    deps = [":tags_lib"],
+)
+
+go_library(
+    name = "tags_lib",
+    srcs = [
+        "tags_lib_bad.go",
+        "tags_lib_good.go",
+    ],
+    importpath = "tags_lib",
+)

tests/core/go_binary/README.rst

@@ -51,3 +51,8 @@ produce static binaries. Verifies `#2168`_.
 
 This test only runs on Linux. The darwin external linker cannot produce
 static binaries since there is no static version of C runtime libraries.
+
+tags_bin
+--------
+Checks that setting ``gotags`` affects source filtering. This binary won't build
+without a specific tag being set.

tests/core/go_binary/tags_lib_bad.go

@@ -0,0 +1,5 @@
+// +build !good
+
+package lib
+
+var Does Not = Compile

tests/core/go_binary/tags_lib_good.go

@@ -0,0 +1 @@
+package lib

tests/core/go_binary/tags_main_bad.go

@@ -0,0 +1,5 @@
+// +build !good
+
+package main
+
+var Does Not = Compile

tests/core/go_binary/tags_main_good.go

@@ -0,0 +1,8 @@
+// +build good
+
+package main
+
+import _ "tags_lib"
+
+func main() {
+}

tests/core/go_test/BUILD.bazel

@@ -157,3 +157,12 @@ go_test(
     ],
     importpath = "example.com/imports/test_main",
 )
+
+go_test(
+    name = "tags_test",
+    srcs = [
+        "tags_bad_test.go",
+        "tags_good_test.go",
+    ],
+    gotags = ["good"],
+)

tests/core/go_test/README.rst

@@ -83,3 +83,9 @@ testmain_import_test
 Check if all packages in all source files are imported to test main, to ensure
 a consistent test behaviour. This ensures a consistent behaviour when thinking
 about global indirect depencencies.
+
+tags_test
+---------
+
+Checks that setting ``gotags`` affects source filtering. The test will fail
+unless a specific tag is set.

tests/core/go_test/tags_bad_test.go

@@ -0,0 +1,9 @@
+// +build !good
+
+package tags_test
+
+import "testing"
+
+func Test(t *testing.T) {
+	t.Fail()
+}

tests/core/go_test/tags_good_test.go

@@ -0,0 +1,7 @@
+// +build good
+
+package tags_test
+
+import "testing"
+
+func Test(t *testing.T) {}