have partials interpreted as template inclusion in mustache_cli

(Before this PR, any use of partials will fail in the command-line
tool.)

Partial names are turned into filenames by adding ".mustache" and then
resolveas paths relative to the current working directory (from which
the tool is invoked, not the directory where the template file
is located). For example, `{{>foo/bar}}` would include
"foo/bar.mustache".

This behavior is used by other command-line mustache processors,
typically the Ruby implementation (`gem install mustache`), so it is
somewhat-standard for a default behavior of partials.

Note: the Ruby implementation also supports {{> ../foo/bar}}, which is
not accepted by our current lexer (partial names must use dots in
a way that would be valid for other tags). The lexer could be relaxed
to allow those, but this can come as a later change.

Author: gasche

CHANGES.md

@@ -1,6 +1,9 @@
 ### 3.2.0
 
-* Improve error messages (@gasche, #47 and #51)
+* Partials are now supported in the `mustache` command-line tool (@gasche, #57)
+  They are interpreted as template inclusion: "{{>foo/bar}}" will include
+  "foo/bar.mustache", relative to the current working directory.
+* Improve error messages (@gasche, #47, #51, #56)
   Note: the exceptions raised by Mustache have changed, this breaks
   compatibility for users that would catch and deconstruct existing
   exceptions.

bin/mustache_cli.ml

@@ -3,26 +3,6 @@ module Mustache = struct
   include With_locations
 end
 
-let apply_mustache ~json_data ~template_filename ~template_data =
-  let env = Ezjsonm.from_string json_data
-  and tmpl =
-    let lexbuf = Lexing.from_string template_data in
-    let () =
-      let open Lexing in
-      lexbuf.lex_curr_p <- { lexbuf.lex_curr_p with pos_fname = template_filename };
-    in
-    try Mustache.parse_lx lexbuf
-    with Mustache.Template_parse_error err ->
-      Format.eprintf "Template parse error:@\n%a@."
-        Mustache.pp_template_parse_error err;
-      exit 3
-  in
-  try Mustache.render tmpl env |> print_endline
-  with Mustache.Render_error err ->
-    Format.eprintf "Template render error:@\n%a@."
-      Mustache.pp_render_error err;
-    exit 2
-
 let load_file f =
   let ic = open_in f in
   let n = in_channel_length ic in
@@ -31,11 +11,34 @@ let load_file f =
   close_in ic;
   (Bytes.to_string s)
 
-let run json_filename template_filename =
-  let json_data = load_file json_filename
-  and template_data = load_file template_filename
+let load_template template_filename =
+  let template_data = load_file template_filename in
+  let lexbuf = Lexing.from_string template_data in
+  let () =
+    let open Lexing in
+    lexbuf.lex_curr_p <- { lexbuf.lex_curr_p with pos_fname = template_filename };
   in
-  apply_mustache ~json_data ~template_filename ~template_data
+  try Mustache.parse_lx lexbuf
+  with Mustache.Template_parse_error err ->
+    Format.eprintf "Template parse error:@\n%a@."
+      Mustache.pp_template_parse_error err;
+    exit 3
+
+let load_json json_filename =
+  Ezjsonm.from_string (load_file json_filename)
+
+let run json_filename template_filename =
+  let env = load_json json_filename in
+  let tmpl = load_template template_filename in
+  let partials name =
+    let path = Printf.sprintf "%s.mustache" name in
+    if not (Sys.file_exists path) then None
+    else Some (load_template path) in
+  try Mustache.render ~partials tmpl env |> print_endline
+  with Mustache.Render_error err ->
+    Format.eprintf "Template render error:@\n%a@."
+      Mustache.pp_render_error err;
+    exit 2
 
 let usage () =
   print_endline "Usage: mustache-cli json_filename template_filename"

bin/test/dune

@@ -0,0 +1,2 @@
+(cram
+ (deps %{bin:mustache}))

bin/test/errors/sys-errors.t

@@ -1,5 +1,5 @@
-  $ touch foo.json
-  $ touch foo.mustache
+  $ echo "{}" > foo.json
+  $ echo "" > foo.mustache
 
 Nonexistent json file:
   $ mustache nonexistent.json foo.mustache

bin/test/partials.t/bar.mustache

@@ -0,0 +1 @@
+{{foo}} {{bar}} !

bin/test/partials.t/data.json

@@ -0,0 +1,4 @@
+{
+    "foo": "Foo",
+    "data": { "bar": "Bar" }
+}

bin/test/partials.t/foo.mustache

@@ -0,0 +1,3 @@
+{{#data}}
+Inside the include is "{{>bar}}"
+{{/data}}

bin/test/partials.t/run.t

@@ -0,0 +1,5 @@
+Simple test:
+
+  $ mustache data.json foo.mustache
+  Inside the include is "Foo Bar !"
+