templates: add pkgstyle-specific template env

pkgstyles can now define TEMPLATE_ENV dict containing variables and
functions available during templating when using that particular style
as well as TEMPLATE_ENV_DYNAMIC dict containing functionas to be
evaluated on template render to fill in dynamic template variables.

New {{ now }} dynamic variable containing current date in suitable
changelog format is now available in templates using deb or rpm
pkgstyles through this new mechanism.

apkg/pkgstyles/deb.py

@@ -12,7 +12,12 @@ and its many clones such as Ubuntu or Mint.
 
  * core: `devscripts`
  * isolated build: `pbuilder`
+
+**template variables:**
+
+ * `now`: current date in Debian changelog format (RFC 2822)
 """
+import email.utils
 import glob
 import os
 from pathlib import Path
@@ -44,6 +49,18 @@ DISTRO_REQUIRES = {
 }
 
 
+def format_date():
+    """
+    current date and time in Debian changelog format (RFC 2822)
+    """
+    return email.utils.formatdate(localtime=True)
+
+
+TEMPLATE_ENV_DYNAMIC = {
+    'now': format_date,
+}
+
+
 RE_PKG_NAME = r'Source:\s*(\S+)'
 # orbital regexp cannon to parse Build-Depends from debian/control
 RE_BUILD_DEPENDS = (

apkg/pkgstyles/rpm.py

@@ -12,7 +12,12 @@ such as Fedora, CentOS, SUSE, RHEL.
 
  * core: `rpm-build`
  * isolated build: `mock`
+
+**template variables:**
+
+ * `now`: current date in RPM changelog format
 """
+from datetime import datetime
 import glob
 from pathlib import Path
 import re
@@ -46,6 +51,18 @@ DISTRO_REQUIRES = {
 }
 
 
+def format_date():
+    """
+    current date and time in RPM changelog format
+    """
+    return datetime.now().strftime('%a %b %d %Y')
+
+
+TEMPLATE_ENV_DYNAMIC = {
+    'now': format_date,
+}
+
+
 RE_PKG_NAME = r'Name:\s*(\S+)'
 RE_BUILD_REQUIRES = r'BuildRequires:\s*(.*)'
 RE_RPMBUILD_OUT_RPM = r'Wrote:\s+(.*\.rpm)\s*'

apkg/pkgtemplate.py

@@ -40,6 +40,24 @@ class PackageTemplate:
             self.style = _pkgstyle.get_pkgstyle_for_template(self.path)
         return self.style
 
+    def template_env(self, env=None):
+        """
+        get/update template env from pkgstyle
+        """
+        # static vars
+        tenv = getattr(self.pkgstyle, 'TEMPLATE_ENV', {})
+        # dynamic vars resolved at render time
+        denv = getattr(self.pkgstyle, 'TEMPLATE_ENV_DYNAMIC', {})
+        if denv:
+            denv_vars = {}
+            for name, fun in denv.items():
+                denv_vars[name] = fun()
+            tenv.update(denv_vars)
+        # custom supplied vars
+        if env:
+            tenv.update(env)
+        return tenv
+
     def render(self, out_path, env,
                render_filter=default_render_filter,
                includes=None, excludes=None):
@@ -72,6 +90,8 @@ class PackageTemplate:
         else:
             out_path.mkdir(parents=True, exist_ok=True)
 
+        env = self.template_env(env=env)
+
         # recursively render all files
         for d, _, files in shutil.walk(self.path):
             rel_dir = Path(d).relative_to(self.path)
@@ -105,6 +125,7 @@ class PackageTemplate:
         render template file in memory and return its content
         """
         src = self.path / name
+        env = self.template_env(env=env)
         with src.open('r') as srcf:
             t = jinja2.Template(srcf.read())
         return t.render(**env) + '\n'

distro/pkg/deb/changelog

 apkg ({{ version }}-{{ release }}) unstable; urgency=medium
 
-  * new upstream version {{ version }} 
+  * upstream version {{ version }}
 
- -- Jakub Ružička <jakub.ruzicka@nic.cz>  Tue, 27 Oct 2020 16:20:00 +0100
+ -- Jakub Ružička <jakub.ruzicka@nic.cz>  {{ now }}

distro/pkg/rpm/apkg.spec

@@ -69,5 +69,5 @@ This package contains apkg module for Python 3.
 
 
 %changelog
-* Mon Mar 01 2021 Jakub Ružička <jakub.ruzicka@nic.cz> - 0.1.0-1
-- initial release
+* {{ now }} Jakub Ružička <jakub.ruzicka@nic.cz> - {{ version }}-{{ release }}
+- upstream version {{ version }}