Add support for including files using the default template processor

The syntax is '{% include "file" %}' where file is either an absolute path or a
path relative to the current template file's directory.

Variables in the included file will be replaced as for the main template. But
the included file can't include files itself.

test/test_unit_template_default.py

@@ -88,6 +88,36 @@ Included section for distro = {LOCAL_DISTRO} ({LOCAL_DISTRO} again)
 end of template
 '''
 
+INCLUDE_BASIC = 'basic\n'
+INCLUDE_VARIABLES = f'''\
+included <{{{{ yadm.class }}}}> file
+
+empty line above
+'''
+INCLUDE_NESTED = 'no newline at the end'
+
+TEMPLATE_INCLUDE = '''\
+The first line
+{% include empty %}
+An empty file removes the line above
+{%include basic%}
+{% include "./variables.{{ yadm.os }}"  %}
+{% include dir/nested %}
+Include basic again:
+{% include basic %}
+'''
+EXPECTED_INCLUDE = f'''\
+The first line
+An empty file removes the line above
+basic
+included <{LOCAL_CLASS}> file
+
+empty line above
+no newline at the end
+Include basic again:
+basic
+'''
+
 
 def test_template_default(runner, yadm, tmpdir):
     """Test template_default"""
@@ -132,3 +162,37 @@ def test_source(runner, yadm, tmpdir):
     assert run.err == ''
     assert output_file.read().strip() == str(input_file)
     assert os.stat(output_file).st_mode == os.stat(input_file).st_mode
+
+
+def test_include(runner, yadm, tmpdir):
+    """Test include"""
+
+    empty_file = tmpdir.join('empty')
+    empty_file.write('', ensure=True)
+
+    basic_file = tmpdir.join('basic')
+    basic_file.write(INCLUDE_BASIC)
+
+    variables_file = tmpdir.join(f'variables.{LOCAL_SYSTEM}')
+    variables_file.write(INCLUDE_VARIABLES)
+
+    nested_file = tmpdir.join('dir').join('nested')
+    nested_file.write(INCLUDE_NESTED, ensure=True)
+
+    input_file = tmpdir.join('input')
+    input_file.write(TEMPLATE_INCLUDE)
+    input_file.chmod(FILE_MODE)
+    output_file = tmpdir.join('output')
+
+    script = f"""
+        YADM_TEST=1 source {yadm}
+        set_awk
+        local_class="{LOCAL_CLASS}"
+        local_system="{LOCAL_SYSTEM}"
+        template_default "{input_file}" "{output_file}"
+    """
+    run = runner(command=['bash'], inp=script)
+    assert run.success
+    assert run.err == ''
+    assert output_file.read() == EXPECTED_INCLUDE
+    assert os.stat(output_file).st_mode == os.stat(input_file).st_mode

yadm

@@ -357,8 +357,13 @@ BEGIN {
   els           = "^{%" blank "*else" blank "*%}$"
   end           = "^{%" blank "*endif" blank "*%}$"
   skp           = "^{%" blank "*(if|else|endif)"
+  inc_start     = "^{%" blank "*include" blank "+\"?"
+  inc_end       = "\"?" blank "*%}$"
+  inc           = inc_start ".+" inc_end
   prt           = 1
+  err           = 0
 }
+END { exit err }
 { replace_vars() } # variable replacements
 $0 ~ vld, $0 ~ end {
   if ($0 ~ vld || $0 ~ end) prt=1;
@@ -370,7 +375,25 @@ $0 ~ vld, $0 ~ end {
   if ($0 ~ els || $0 ~ end) prt=1;
   if ($0 ~ skp) next;
 }
-{ if (prt) print }
+{ if (!prt) next }
+$0 ~ inc {
+  file = $0
+  sub(inc_start, "", file)
+  sub(inc_end, "", file)
+  sub(/^[^\/].*$/, source_dir "/&", file)
+
+  while ((res = getline <file) > 0) {
+    replace_vars()
+    print
+  }
+  if (res < 0) {
+    printf "%s:%d: error: could not read '%s'\n", FILENAME, NR, file | "cat 1>&2"
+    err = 1
+  }
+  close(file)
+  next
+}
+{ print }
 function replace_vars() {
   for (label in c) {
     gsub(("{{" blank "*yadm\\." label blank "*}}"), c[label])
@@ -396,8 +419,9 @@ EOF
     -v user="$local_user" \
     -v distro="$local_distro" \
     -v source="$input" \
+    -v source_dir="$(dirname "$input")" \
     "$awk_pgm" \
-    "$input" > "$temp_file"
+    "$input" > "$temp_file" || rm -f "$temp_file"
 
   if [ -f "$temp_file" ] ; then
     copy_perms "$input" "$temp_file"

yadm.1

@@ -708,6 +708,7 @@ with the following content
   config={{yadm.class}}-{{yadm.os}}
   {% else %}
   config=dev-whatever
+  {% include "whatever.extra" %}
   {% endif %}
 
 would output a file named
@@ -716,9 +717,12 @@ with the following content if the user is "harvey":
 
   config=work-Linux
 
-and the following otherwise:
+and the following otherwise (if
+.I whatever.extra
+contains admin=false):
 
   config=dev-whatever
+  admin=false
 
 An equivalent Jinja template named
 .I whatever##template.j2
@@ -728,6 +732,7 @@ would look like:
   config={{YADM_CLASS}}-{{YADM_OS}}
   {% else -%}
   config=dev-whatever
+  {% include 'whatever.extra' %}
   {% endif -%}
 
 An equivalent ESH templated named
@@ -738,6 +743,7 @@ would look like:
   config=<%= $YADM_CLASS %>-<%= $YADM_OS %>
   <% else -%>
   config=dev-whatever
+  <%+ whatever.extra %>
   <% fi -%>
 
 .SH ENCRYPTION