Add jinja processing to alt command

With the new functionality, when the 'alt' command is called (or automatically
triggered), any file with a name ending in '##yadm_tmpl' is treated as a jinja
template. The template is processed by envtpl and the result is written to a
file without the '##yadm_tmpl' name. The variables passed into the template
processing are

  YADM_CLASS
  YADM_OS
  YADM_HOSTNAME
  YADM_USER

These variables are set according to the normal rules for
CLASS, OS, HOSTNAME, and USER during the alt processing.

test/113_accept_jinja_alt.bats

@@ -0,0 +1,151 @@
+load common
+load_fixtures
+status=;output=; #; populated by bats run()
+
+IN_REPO=(alt* "dir one")
+export TEST_TREE_WITH_ALT=1
+
+
+setup() {
+  destroy_tmp
+  build_repo "${IN_REPO[@]}"
+}
+
+
+function test_alt() {
+  local alt_type="$1"
+  local test_overwrite="$2"
+  local auto_alt="$3"
+
+  #; detemine test parameters
+  case $alt_type in
+    base)
+      real_name="alt-jinja"
+      file_content_match="-${T_SYS}-${T_HOST}-${T_USER}"
+    ;;
+    override_all)
+      real_name="alt-jinja"
+      file_content_match="custom_class-custom_system-custom_host-custom_user"
+    ;;
+  esac
+
+  if [ "$test_overwrite" = "true" ] ; then
+    #; create incorrect links (to overwrite)
+    echo "BAD_CONTENT" "$T_DIR_WORK/$real_name"
+  else
+    #; verify real file doesn't already exist
+    if [ -e "$T_DIR_WORK/$real_name" ] ; then
+      echo "ERROR: real file already exists before running yadm"
+      return 1
+    fi
+  fi
+
+  #; configure yadm.auto_alt=false
+  if [ "$auto_alt" = "false" ]; then
+    git config --file="$T_YADM_CONFIG" yadm.auto-alt false
+  fi
+
+  #; run yadm (alt or status)
+  if [ -z "$auto_alt" ]; then
+    run "${T_YADM_Y[@]}" alt
+    #; validate status and output
+    if [ "$status" != 0 ] || [[ ! "$output" =~ Creating.+$real_name ]]; then
+      echo "OUTPUT:$output"
+      echo "ERROR: Could not confirm status and output of alt command"
+      return 1;
+    fi
+  else
+    #; running any passed through Git command should trigger auto-alt
+    run "${T_YADM_Y[@]}" status
+    if [ -n "$auto_alt" ] && [[ "$output" =~ Creating.+$real_name ]]; then
+      echo "ERROR: Reporting of jinja processing should not happen"
+      return 1
+    fi
+  fi
+
+  #; validate link content
+  if [[ "$alt_type" =~ none ]] || [ "$auto_alt" = "false" ]; then
+    #; no real file should be present
+    if [ -L "$T_DIR_WORK/$real_name" ] ; then
+      echo "ERROR: Real file should not exist"
+      return 1
+    fi
+  else
+    #; correct real file should be present
+    local file_content
+    file_content=$(cat "$T_DIR_WORK/$real_name")
+    if [ "$file_content" != "$file_content_match" ]; then
+      echo "file_content: ${file_content}"
+      echo "expected_content: ${file_content_match}"
+      echo "ERROR: Link content is not correct"
+      return 1
+    fi
+  fi
+}
+
+@test "Command 'alt' (select jinja)" {
+  echo "
+    When the command 'alt' is provided
+    and file matches ##yadm_tmpl
+    Report jinja template processing
+    Verify that the correct content is written
+    Exit with 0
+  "
+
+  test_alt 'base' 'false' ''
+}
+
+@test "Command 'auto-alt' (enabled)" {
+  echo "
+    When a command possibly changes the repo
+    and auto-alt is configured true
+    and file matches ##yadm_tmpl
+    automatically process alternates
+    report no linking (not loud)    
+    Verify that the correct content is written
+  "
+
+  test_alt 'base' 'false' 'true'
+}
+
+@test "Command 'auto-alt' (disabled)" {
+  echo "
+    When a command possibly changes the repo
+    and auto-alt is configured false
+    and file matches ##yadm_tmpl
+    Report no jinja template processing
+    Verify no content
+  "
+
+  test_alt 'base' 'false' 'false'
+}
+
+@test "Command 'alt' (overwrite existing content)" {
+  echo "
+    When the command 'alt' is provided
+    and file matches ##yadm_tmpl
+    and the real file exists, and is wrong
+    Report jinja template processing
+    Verify that the correct content is written
+    Exit with 0
+  "
+
+  test_alt 'base' 'true' ''
+}
+
+@test "Command 'alt' (overwritten settings)" {
+  echo "
+    When the command 'alt' is provided
+    and file matches ##yadm_tmpl
+    after setting local.*
+    Report jinja template processing
+    Verify that the correct content is written
+    Exit with 0
+  "
+
+  GIT_DIR="$T_DIR_REPO" git config local.os custom_system
+  GIT_DIR="$T_DIR_REPO" git config local.user custom_user
+  GIT_DIR="$T_DIR_REPO" git config local.host custom_host
+  GIT_DIR="$T_DIR_REPO" git config local.class custom_class
+  test_alt 'override_all' 'false' ''
+}

test/common.bash

@@ -202,8 +202,10 @@ function create_worktree() {
       make_parents "$DIR_WORKTREE/$f"
       echo "$f" > "$DIR_WORKTREE/$f"
     done
+    echo "{{ YADM_CLASS }}-{{ YADM_OS }}-{{ YADM_HOSTNAME }}-{{ YADM_USER }}" > "$DIR_WORKTREE/alt-jinja##yadm_tmpl"
   fi
 
+
   if [ ! -z "$TEST_TREE_WITH_WILD" ] ; then
     #; wildcard test data - yes this is a big mess :(
     #; none

yadm

@@ -114,30 +114,32 @@ function alt() {
 
   require_repo
 
-  match_class="$(config local.class)"
+  local_class="$(config local.class)"
-  if [ -z "$match_class" ] ; then
+  if [ -z "$local_class" ] ; then
     match_class="%"
+  else
+    match_class="$local_class"
   fi
   match_class="(%|$match_class)"
 
-  match_system="$(config local.os)"
+  local_system="$(config local.os)"
-  if [ -z "$match_system" ] ; then
+  if [ -z "$local_system" ] ; then
-    match_system=$(uname -s)
+    local_system=$(uname -s)
   fi
-  match_system="(%|$match_system)"
+  match_system="(%|$local_system)"
 
-  match_host="$(config local.host)"
+  local_host="$(config local.host)"
-  if [ -z "$match_host" ] ; then
+  if [ -z "$local_host" ] ; then
-    match_host=$(hostname)
+    local_host=$(hostname)
-    match_host=${match_host%%.*} #; trim any domain from hostname
+    local_host=${local_host%%.*} #; trim any domain from hostname
   fi
-  match_host="(%|$match_host)"
+  match_host="(%|$local_host)"
 
-  match_user="$(config local.user)"
+  local_user="$(config local.user)"
-  if [ -z "$match_user" ] ; then
+  if [ -z "$local_user" ] ; then
-    match_user=$(id -u -n)
+    local_user=$(id -u -n)
   fi
-  match_user="(%|$match_user)"
+  match_user="(%|$local_user)"
 
   #; regex for matching "<file>##CLASS.SYSTEM.HOSTNAME.USER"
   match1="^(.+)##(()|$match_system|$match_system\.$match_host|$match_system\.$match_host\.$match_user)$"
@@ -193,6 +195,30 @@ function alt() {
     done
   done
 
+  #; loop over all "tracked" files
+  #; for every file which is a *##yadm_tmpl create a real file
+  local IFS=$'\n'
+  local match="^(.+)##yadm_tmpl"
+  local envtpl_bin=$(which envtpl) 
+  for tracked_file in $("$GIT_PROGRAM" ls-files | sort) $(cat "$YADM_ENCRYPT" 2>/dev/null); do
+    tracked_file="$YADM_WORK/$tracked_file"
+    if [ -e "$tracked_file" ] ; then
+      if [[ $tracked_file =~ $match ]] ; then
+        if [[ -z "$envtpl_bin" ]]; then
+          debug "'envtpl' (pip install envtpl) not available, not creating $real_file from template $tracked_file"
+          [ -n "$loud" ] && echo "'envtpl' (pip install envtpl) not available, not creating $real_file from template $tracked_file"
+        else
+          real_file="${BASH_REMATCH[1]}"
+          debug "Creating $real_file from template $tracked_file"
+          [ -n "$loud" ] && echo "Creating $real_file from template $tracked_file"
+          YADM_CLASS="$local_class" YADM_OS="$local_system" \
+          YADM_HOSTNAME="$local_host" YADM_USER="$local_user" \
+          $envtpl_bin < $tracked_file > $real_file
+        fi
+      fi
+    fi
+  done
+
 }
 
 function bootstrap() {

yadm.1

@@ -89,7 +89,8 @@ Instead use the
 command (see below).
 .TP
 .B alt
-Create symbolic links for any managed files matching the naming rules describe in the ALTERNATES section.
+Create symbolic links and process jinja templates for any managed files matching the naming rules describe 
+in the ALTERNATES section. 
 It is usually unnecessary to run this command, as
 .B yadm
 automatically processes alternates by default.
@@ -473,6 +474,43 @@ using the configuration options
 and
 .BR local.user .
 
+If 
+.BR envtpl
+(
+.BR pip\ install\ envtpl
+) is available, you can also create 
+.B jinja
+templates (http://jinja.pocoo.org/) which will transformed into real files. 
+.B yadm
+will treat files ending in 
+
+ ##yadm_tmpl
+
+as jinja templates. During processing, the following variables are 
+set according to the above rules:
+
+ YADM_CLASS
+ YADM_OS
+ YADM_HOSTNAME
+ YADM_USER
+
+E.g. a file 'whatever##yadm_tmpl' with the following content
+
+ {% if YADM_USER == 'harvey' -%}
+ config={{YADM_CLASS}}-{{ YADM_OS }}
+ {% else -%}
+ config=dev-whatever
+ {% endif -%}
+
+would output a file with the follwing content, if the username would be 'harvey'
+
+ config=work-Linux
+
+and the following otherwise:
+
+ config=dev-whatever
+
+
 .SH ENCRYPTION
 It can be useful to manage confidential files, like SSH or GPG keys, across
 multiple systems. However, doing so would put plain text data into a Git