pretty printer doesn't know how to print the omitted type `_` marker

[pnkfelix]

pretty printer doesn't know how to print the omitted type _ marker

example:

fn main() {
    fn f1(x: i32, y: i32) -> i32 { y }
    let f: fn(_, i32) -> i32 = f1;
    //        ~
    //        |
    //        +--- this is pretty-printed badly.
    f(13);
}

pretty prints this way:

% ./x86_64-apple-darwin/stage1/bin/rustc --pretty -Z unstable-options pp-1.rs
fn main() {
    fn f1(x: i32, y: i32) -> i32 { y }
    let f: fn(, i32) -> i32 = f1;
    //        ~
    //        |
    //        +--- this is pretty-printed badly.
    f(13);
}
% 

[nxnfufunezn]

I am taking this...

[eddyb]

Cause is this special-casing in print_arg, originally intended for closures. HIR pretty-printing might have something similar. I believe the fix would be to propagate a bool or some enum down to print_arg to distinguish between closures and everything else.

[nxnfufunezn]

@eddyb So adding another param to print_arg would be good idea to distinguish between closures ??

[eddyb]

@nxnfufunezn Yes, but also to print_fn_args, which is called by print_fn_args_and_ret which should always print types and print_fn_block_args which shouldn't print TyInfer (because it's used for closures).

[nxnfufunezn]

@eddyb And what about arg_to_string ?

here is what I did..

diff --git a/src/libsyntax/print/pprust.rs b/src/libsyntax/print/pprust.rs
index 67817ee..685f1e9 100644
--- a/src/libsyntax/print/pprust.rs
+++ b/src/libsyntax/print/pprust.rs
@@ -425,7 +425,7 @@ pub fn variant_to_string(var: &ast::Variant) -> String {
 }

 pub fn arg_to_string(arg: &ast::Arg) -> String {
-    to_string(|s| s.print_arg(arg))
+    to_string(|s| s.print_arg(arg, false))
 }

 pub fn mac_to_string(arg: &ast::Mac) -> String {
@@ -2672,7 +2672,7 @@ impl<'a> State<'a> {
     }

     pub fn print_fn_args(&mut self, decl: &ast::FnDecl,
-                         opt_explicit_self: Option<&ast::ExplicitSelf_>)
+                         opt_explicit_self: Option<&ast::ExplicitSelf_>, is_closure: bool)
         -> io::Result<()> {
         // It is unfortunate to duplicate the commasep logic, but we want the
         // self type and the args all in the same box.
@@ -2698,7 +2698,7 @@ impl<'a> State<'a> {

         for arg in args {
             if first { first = false; } else { try!(self.word_space(",")); }
-            try!(self.print_arg(arg));
+            try!(self.print_arg(arg, is_closure));
         }

         self.end()
@@ -2708,7 +2708,7 @@ impl<'a> State<'a> {
                                  opt_explicit_self: Option<&ast::ExplicitSelf_>)
         -> io::Result<()> {
         try!(self.popen());
-        try!(self.print_fn_args(decl, opt_explicit_self));
+        try!(self.print_fn_args(decl, opt_explicit_self, true));
         if decl.variadic {
             try!(word(&mut self.s, ", ..."));
         }
@@ -2722,7 +2722,7 @@ impl<'a> State<'a> {
             decl: &ast::FnDecl)
             -> io::Result<()> {
         try!(word(&mut self.s, "|"));
-        try!(self.print_fn_args(decl, None));
+        try!(self.print_fn_args(decl, None, false));
         try!(word(&mut self.s, "|"));

         if let ast::DefaultReturn(..) = decl.output {
@@ -2967,10 +2967,10 @@ impl<'a> State<'a> {
         self.print_type(&*mt.ty)
     }

-    pub fn print_arg(&mut self, input: &ast::Arg) -> io::Result<()> {
+    pub fn print_arg(&mut self, input: &ast::Arg, is_closure: bool) -> io::Result<()> {
         try!(self.ibox(INDENT_UNIT));
         match input.ty.node {
-            ast::TyInfer => try!(self.print_pat(&*input.pat)),
+            ast::TyInfer if is_closure == true => try!(self.print_pat(&*input.pat)),
             _ => {
                 match input.pat.node {
                     ast::PatIdent(_, ref path1, _) if

Still getting this --

fn main() {
    fn f1(x: i32, y: i32) -> i32 { y }
    let f: fn(, i32) -> i32 = f1;
    //        ~
    //        |
    //        +--- this is pretty-printed badly.
    f(13);
}

[eddyb]

@nxnfufunezn It looks good, but you got the closure and non-closure cases swapped (the one with "|" is the closure case).

Btw, if is_closure == true can be just if is_closure.

[nxnfufunezn]

okay..

[nxnfufunezn]

should do for hir also...