Fix #1019

Signed-off-by: Jeremie Dimino <jeremie@dimino.org>

src/usexp/dune_lexer.mll

@@ -282,7 +282,7 @@ and quoted_string_after_escaped_newline = parse
     { quoted_string lexbuf }
 
 and template_variable = parse
-  | (varname_char+ as name) (':' (varname_char* as payload))? '}'
+  | (varname_char+ as name) (':' ((':' | varname_char)* as payload))? '}'
     { let payload =
         match payload with
         | Some "" -> error lexbuf "payload after : in variable cannot be empty"

test/blackbox-tests/test-cases/github1019/dune

@@ -1,5 +1,5 @@
-(library (name foo))
+(library (name foo) (public_name foo))
 
 (alias
  (name default)
- (echo %{lib:foo:foo.ml}))
+ (action (echo %{lib:foo:foo.ml})))

test/blackbox-tests/test-cases/github1019/run.t

@@ -1,6 +1,4 @@
 Regression test for #1019
 
   $ dune build
-  File "dune", line 5, characters 9-10:
-  Error: This character is not allowed inside %{...} forms
-  [1]
+  ../install/default/lib/foo/foo.ml