Improve error message for closing tokens in parse_atom (#261)

Fixes #114

Author: c42f

src/parser.jl

@@ -3557,7 +3557,7 @@ function parse_atom(ps::ParseState, check_identifiers=true)
         # )  ==>  error
         msg = leading_kind == K"EndMarker" ?
               "premature end of input" :
-              "unexpected closing token"
+              "unexpected `$(untokenize(leading_kind))`"
         bump_invisible(ps, K"error", error=msg)
     else
         bump(ps, error="invalid syntax atom")

test/diagnostics.jl

@@ -24,6 +24,9 @@ end
     # TODO: better range
 	@test diagnostic("@A.\$x a") ==
         Diagnostic(6, 5, :error, "invalid macro name")
+
+	@test diagnostic("a, , b") ==
+        Diagnostic(4, 3, :error, "unexpected `,`")
 end
 
 @testset "parser warnings" begin