Add option for base platform tc definition

Author: nradakovic

examples/.bazelrc

@@ -24,19 +24,19 @@ build:shared --host_platform=@score_bazel_platforms//:x86_64-linux
 # Config dedicated to host platform CPU:x86_64 and OS:Linux
 # -------------------------------------------------------------------------------
 build:x86_64-linux --config=shared
-build:x86_64-linux --platforms=@score_bazel_platforms//:x86_64-linux-gcc_12.2.0-posix
 
 # -------------------------------------------------------------------------------
 # Different toolchain configuration for x86_64-linux
 # -------------------------------------------------------------------------------
 build:host_config_1 --config=x86_64-linux
-build:host_config_1 --extra_toolchains=@score_gcc_toolchain//:x86_64-linux-gcc_12.2.0-posix
+build:host_config_1 --extra_toolchains=@score_gcc_toolchain//:x86_64-linux
 build:host_config_1 --features=use_pthread
 
 # -------------------------------------------------------------------------------
 # Different toolchain configuration for x86_64-linux
 # -------------------------------------------------------------------------------
 build:host_config_2 --config=x86_64-linux
+build:host_config_2 --platforms=@score_bazel_platforms//:x86_64-linux-gcc_12.2.0-posix
 build:host_config_2 --extra_toolchains=@my_toolchain//:x86_64-linux-gcc_12.2.0-posix
 
 # -------------------------------------------------------------------------------

examples/MODULE.bazel

@@ -70,6 +70,7 @@ gcc.toolchain(
     target_os = "linux",
     version = "12.2.0",
     use_default_package = True,
+    use_base_constraints_only = True,
 )
 
 # *******************************************************************************

extensions/gcc.bzl

@@ -62,12 +62,16 @@ _attrs_tc = {
     ),
     "use_system_toolchain": attr.bool(
         default = False,
-        doc = "TBD",
+        doc = "Flag for toolchain creation to use host installed binaries. Not yet supported!",
+    ),
+    "use_base_constraints_only": attr.bool(
+        default = False,
+        doc = "Experimental. Attribute for flag toolchain creation to use only base platform constraints. Limits toolchain registration to 1 per base platform definition."
     ),
     "runtime_ecosystem": attr.string(
         default = "posix",
         mandatory = False,
-        doc = "TBD",
+        doc = "Attribute for identifing the system-level runtime environment a binary or target is built to run in.",
     ),
     "target_cpu": attr.string(
         mandatory = True,
@@ -162,6 +166,7 @@ def _get_toolchains(tags):
             "sdp_to_link": tag.sdp_to_link,
             "use_default_package": tag.use_default_package,
             "use_system_toolchain": tag.use_system_toolchain,
+            "use_base_constraints_only": tag.use_base_constraints_only,
             "tc_extra_compile_flags": tag.extra_compile_flags,
             "tc_extra_link_flags": tag.extra_link_flags,
             "sdp_version": tag.sdp_version,
@@ -263,6 +268,7 @@ def _impl(mctx):
             gcc_version = toolchain_info["tc_version"],
             cc_toolchain_config = toolchain_info["cc_toolchain_config"],
             cc_toolchain_flags = toolchain_info["cc_toolchain_flags"],
+            use_base_constraints_only = toolchain_info["use_base_constraints_only"]
         )
 
 gcc = module_extension(

rules/gcc.bzl

@@ -101,6 +101,16 @@ def _impl(rctx):
     else:
         fail("Unsupported OS detected!")
 
+    tc_identifier_short_1 = ""
+    tc_identifier_long_1 = "[]"
+    tc_identifier_short_2 = ""
+    tc_identifier_long_2 = "[]"
+    if not rctx.attr.use_base_constraints_only:
+        tc_identifier_short_1 = "-{}".format(tc_identifier)
+        tc_identifier_long_1 = "[\"@score_bazel_platforms//version:{}\"]".format(tc_identifier)
+        tc_identifier_short_2 = "-{}".format(rctx.attr.tc_runtime_ecosystem)
+        tc_identifier_long_2 = "[\"@score_bazel_platforms//runtime_es:{}\"]".format(rctx.attr.tc_runtime_ecosystem)
+
     rctx.template(
         "BUILD",
         rctx.attr._cc_toolchain_build,
@@ -110,15 +120,16 @@ def _impl(rctx):
             "%{tc_cpu}": rctx.attr.tc_cpu,
             "%{tc_os}": rctx.attr.tc_os,
             "%{tc_version}": rctx.attr.gcc_version,
-            "%{tc_identifier}": tc_identifier, 
-            "%{tc_runtime_es}": rctx.attr.tc_runtime_ecosystem,
+            "%{tc_identifier_short_1}": tc_identifier_short_1,
+            "%{tc_identifier_short_2}": tc_identifier_short_2,
+            "%{tc_identifier_long_1}": tc_identifier_long_1,
+            "%{tc_identifier_long_2}": tc_identifier_long_2,
         },
     )
 
     extra_compile_flags = get_flag_groups(rctx.attr.extra_compile_flags)
     extra_link_flags = get_flag_groups(rctx.attr.extra_link_flags)
 
-
     template_dict = {
         "%{tc_version}": rctx.attr.gcc_version,
         "%{tc_identifier}": "gcc",
@@ -188,6 +199,7 @@ gcc_toolchain = repository_rule(
         "cc_toolchain_flags": attr.label(
             doc = "Path to the Bazel BUILD file template for the toolchain.",
         ),
+        "use_base_constraints_only": attr.bool(doc="Boolean flag to state only base constraints should be used for toolchain compatibility definition"),
         "_cc_toolchain_build": attr.label(
             default = "@score_bazel_cpp_toolchains//templates:BUILD.template",
             doc = "Path to the Bazel BUILD file template for the toolchain.",

templates/BUILD.template

@@ -37,18 +37,19 @@ cc_toolchain(
     toolchain_config = ":cc_toolchain_config",
 )
 
+# "@score_bazel_platforms//version:%{tc_runtime_es}",
+# "@score_bazel_platforms//version:%{tc_identifier}",
+
 toolchain(
-    name = "%{tc_cpu}-%{tc_os}-%{tc_identifier}-%{tc_runtime_es}",
+    name = "%{tc_cpu}-%{tc_os}%{tc_identifier_short_1}%{tc_identifier_short_2}",
     exec_compatible_with = [
         "@platforms//cpu:x86_64",
         "@platforms//os:linux",
     ],
     target_compatible_with = [
         "@platforms//cpu:%{tc_cpu}",
         "@platforms//os:%{tc_os}",
-        "@score_bazel_platforms//runtime_es:%{tc_runtime_es}",
-        "@score_bazel_platforms//version:%{tc_identifier}",
-    ],
+    ] + %{tc_identifier_long_1} + %{tc_identifier_long_2},
     toolchain = ":cc_toolchain",
     toolchain_type = "@bazel_tools//tools/cpp:toolchain_type",
     visibility = [