Expand make variables in env

foreign_cc/built_tools/private/built_tools_framework.bzl

@@ -8,7 +8,7 @@ load("//foreign_cc/private/framework:helpers.bzl", "convert_shell_script", "sheb
 # Common attributes for all built_tool rules
 FOREIGN_CC_BUILT_TOOLS_ATTRS = {
     "env": attr.string_dict(
-        doc = "Environment variables to set during the build.",
+        doc = "Environment variables to set during the build. This attribute is subject to make variable substitution.",
         default = {},
     ),
     "srcs": attr.label(

foreign_cc/cmake.bzl

@@ -143,6 +143,7 @@ load(
     "cc_external_rule_impl",
     "create_attrs",
     "expand_locations",
+    "expand_make_variables",
 )
 load("//foreign_cc/private:transitions.bzl", "make_variant")
 load(
@@ -262,7 +263,7 @@ def _create_configure_script(configureParameters):
         root = root,
         no_toolchain_file = no_toolchain_file,
         user_cache = dict(ctx.attr.cache_entries),
-        user_env = expand_locations(ctx, ctx.attr.env, data),
+        user_env = expand_locations(ctx, expand_make_variables(ctx, "env", ctx.attr.env), data),
         options = attrs.generate_args,
         cmake_commands = cmake_commands,
         cmake_prefix = prefix,

foreign_cc/configure.bzl

@@ -17,6 +17,7 @@ load(
     "cc_external_rule_impl",
     "create_attrs",
     "expand_locations",
+    "expand_make_variables",
 )
 load("//foreign_cc/private:transitions.bzl", "make_variant")
 load("//foreign_cc/private/framework:platform.bzl", "os_name")
@@ -74,7 +75,7 @@ def _create_configure_script(configureParameters):
         for arg in ctx.attr.args
     ])
 
-    user_env = expand_locations(ctx, ctx.attr.env, data)
+    user_env = expand_locations(ctx, expand_make_variables(ctx, "env", ctx.attr.env), data)
 
     make_commands = []
     prefix = "{} ".format(expand_locations(ctx, attrs.tool_prefix, data)) if attrs.tool_prefix else ""

foreign_cc/private/framework.bzl

@@ -103,6 +103,7 @@ CC_EXTERNAL_RULE_ATTRIBUTES = {
             "`$(execpath)` macros may be used to point at files which are listed as `data`, `deps`, or `build_data`, " +
             "but unlike with other rules, these will be replaced with absolute paths to those files, " +
             "because the build does not run in the exec root. " +
+            "This attribute is subject to make variable substitution. " +
             "No other macros are supported." +
             "Variables containing `PATH` (e.g. `PATH`, `LD_LIBRARY_PATH`, `CPATH`) entries will be prepended to the existing variable."
         ),
@@ -952,3 +953,21 @@ def expand_locations(ctx, expandable, data):
             return ctx.expand_location(expandable.replace("$(execpath ", "$$EXT_BUILD_ROOT$$/$(execpath "), data)
     else:
         fail("Unsupported type: {}".format(type(expandable)))
+
+def expand_make_variables(ctx, attr_name, data):
+    """Expand make variables on a dictionary
+
+    See https://docs.bazel.build/versions/main/be/make-variables.html
+
+    Args:
+        ctx (ctx): The rule's context object
+        attr_name (str): Name of the attr of the rule being expanded
+        data (dict): Dict whose values to expand (must be dict[str, str])
+
+    Returns:
+        dict: An expanded dict of environment variables
+    """
+    return {
+        k: ctx.expand_make_variables(attr_name, v, {})
+        for k, v in data.items()
+    }