Add a "build-script" constraint enabled in build script platforms

Author: dtolnay

constraints/BUCK

@@ -32,6 +32,10 @@ constraint(
     ],
 )
 
+constraint(
+    setting = "build-script",
+)
+
 constraint(
     setting = "opt-level",
     values = [

platforms/defs.bzl

@@ -66,6 +66,7 @@ platform = rule(
         # this list are preserved.
         "transition": attrs.list(attrs.configuration_label(), default = [
             "//constraints:bootstrap-stage",
+            "//constraints:build-script",
             "//constraints:opt-level",
             "//constraints:sysroot-deps",
             "//constraints:workspace",

platforms/stage1/BUCK

@@ -16,6 +16,7 @@ platform(
     name = "library-build-script",
     base = ":library",
     constraint_values = [
+        "//constraints:build-script",
         "//constraints:opt-level=0",
         "//constraints:sysroot-deps=implicit",
     ],
@@ -38,6 +39,7 @@ platform(
     name = "compiler-build-script",
     base = ":compiler",
     constraint_values = [
+        "//constraints:build-script",
         "//constraints:opt-level=0",
     ],
     visibility = ["PUBLIC"],

platforms/stage2/BUCK

@@ -16,6 +16,7 @@ platform(
     name = "library-build-script",
     base = ":library",
     constraint_values = [
+        "//constraints:build-script",
         "//constraints:opt-level=0",
         "//constraints:sysroot-deps=implicit",
     ],
@@ -38,6 +39,7 @@ platform(
     name = "compiler-build-script",
     base = ":compiler",
     constraint_values = [
+        "//constraints:build-script",
         "//constraints:opt-level=0",
     ],
     visibility = ["PUBLIC"],

toolchains/cxx/BUCK

@@ -5,6 +5,7 @@ configuration_transition(
     name = "prune_cxx_configuration",
     discard_settings = [
         "rust//constraints:bootstrap-stage",
+        "rust//constraints:build-script",
         "rust//constraints:sysroot-deps",
         "rust//constraints:workspace",
     ],