meson: replace some m4 templates with jinja2

m4 was nice in '85, but the syntax feels a bit dated. Since we use python for
meson, let's use a popular python templating engine to replace some m4 usage.

A little nicety is that typos are caught:

FAILED: sysusers.d/systemd-remote.conf
/usr/bin/meson --internal exe --capture sysusers.d/systemd-remote.conf -- /home/zbyszek/src/systemd/tools/meson-render-jinja2.py config.h ../sysusers.d/systemd-remote.conf.j2
Traceback (most recent call last):
  File "/home/zbyszek/src/systemd/tools/meson-render-jinja2.py", line 28, in <module>
    print(render(sys.argv[2], defines))
  File "/home/zbyszek/src/systemd/tools/meson-render-jinja2.py", line 24, in render
    return template.render(defines)
  File "/usr/lib/python3.9/site-packages/jinja2/environment.py", line 1090, in render
    self.environment.handle_exception()
  File "/usr/lib/python3.9/site-packages/jinja2/environment.py", line 832, in handle_exception
    reraise(*rewrite_traceback_stack(source=source))
  File "/usr/lib/python3.9/site-packages/jinja2/_compat.py", line 28, in reraise
    raise value.with_traceback(tb)
  File "<template>", line 8, in top-level template code
jinja2.exceptions.UndefinedError: 'HAVE_MICROHTTP' is undefined

This checking mirrors what 349cc4a507c4d84fcadf61f42159ea6412717896 did for C defines.

1 files changed, 28 insertions, 0 deletions

diff --git a/tools/meson-render-jinja2.py b/tools/meson-render-jinja2.py
new file mode 100755
index 0000000000..063cb0eb27
--- /dev/null
+++ b/tools/meson-render-jinja2.py
@@ -0,0 +1,28 @@
+#!/usr/bin/env python3
+# SPDX-License-Identifier: LGPL-2.1+
+
+import jinja2
+import re
+import sys
+
+def parse_config_h(filename):
+    # Parse config.h file generated by meson.
+    ans = {}
+    for line in open(filename):
+        m = re.match(r'#define\s+(\w+)\s+(.*)', line)
+        if not m:
+            continue
+        a, b = m.groups()
+        if b and b[0] in '0123456789"':
+            b = eval(b)
+        ans[a] = b
+    return ans
+
+def render(filename, defines):
+    text = open(filename).read()
+    template = jinja2.Template(text, trim_blocks=True, undefined=jinja2.StrictUndefined)
+    return template.render(defines)
+
+if __name__ == '__main__':
+    defines = parse_config_h(sys.argv[1])
+    print(render(sys.argv[2], defines))