feat: expand_template does execpath and vars substitutions (#6)

Author: alexeagle

docs/expand_make_vars.md

@@ -15,6 +15,11 @@ Template expansion
 This performs a simple search over the template file for the keys in substitutions,
 and replaces them with the corresponding values.
 
+Values may also use location templates as documented in [expand_locations](#expand_locations)
+as well as [configuration variables] such as `$(BINDIR)`, `$(TARGET_CPU)`, and `$(COMPILATION_MODE)`.
+
+[configuration variables]: https://docs.bazel.build/versions/main/skylark/lib/ctx.html#var
+
 
 **ATTRIBUTES**
 

lib/private/expand_make_vars.bzl

@@ -164,13 +164,18 @@ def expand_variables(ctx, s, outs = [], output_dir = False, attribute_name = "ar
     return ctx.expand_make_variables(attribute_name, s, additional_substitutions)
 
 def _expand_template_impl(ctx):
+    template = ctx.file.template
+    substitutions = ctx.attr.substitutions
+
+    subs = dict({
+        k: expand_locations(ctx, v, ctx.attr.data)
+        for k, v in substitutions.items()
+    }, **ctx.var)
+
     ctx.actions.expand_template(
-        template = ctx.file.template,
+        template = template,
         output = ctx.outputs.out,
-        substitutions = {
-            k: expand_locations(v, ctx.attr.data)
-            for k, v in ctx.attr.substitutions.items()
-        },
+        substitutions = subs,
         is_executable = ctx.attr.is_executable,
     )
 
@@ -179,6 +184,11 @@ expand_template = struct(
     
 This performs a simple search over the template file for the keys in substitutions,
 and replaces them with the corresponding values.
+
+Values may also use location templates as documented in [expand_locations](#expand_locations)
+as well as [configuration variables] such as `$(BINDIR)`, `$(TARGET_CPU)`, and `$(COMPILATION_MODE)`.
+
+[configuration variables]: https://docs.bazel.build/versions/main/skylark/lib/ctx.html#var
 """,
     implementation = _expand_template_impl,
     attrs = {

lib/tests/BUILD.bazel

@@ -1,3 +1,7 @@
+"tests for libs"
+
+load("@bazel_skylib//rules:write_file.bzl", "write_file")
+load("//lib:expand_make_vars.bzl", "expand_template")
 load(":expand_make_vars_test.bzl", "expand_make_vars_test_suite")
 load(":utils_test.bzl", "utils_test_suite")
 load(":paths_test.bzl", "paths_test_suite")
@@ -7,3 +11,32 @@ expand_make_vars_test_suite()
 paths_test_suite()
 
 utils_test_suite()
+
+write_file(
+    name = "gen_template",
+    out = "template.txt",
+    content = [
+        "#!/bin/bash",
+        "set -o errexit",
+        """[ "{thing}" == "stuff" ]""",
+        """[ "%path%" == "BINDIR/lib/tests/template.txt" ]""",
+    ],
+)
+
+expand_template(
+    name = "expand_template",
+    out = "expand_template_test.sh",
+    data = [":gen_template"],
+    is_executable = True,
+    substitutions = {
+        "{thing}": "stuff",
+        "%path%": "$(execpath :gen_template)",
+        "BINDIR": "$(BINDIR)",
+    },
+    template = "template.txt",
+)
+
+sh_test(
+    name = "expand_template_test",
+    srcs = ["expand_template"],
+)