Auto merge of #40346 - jseyfried:path_and_tokenstream_attr, r=nrc

`TokenStream`-based attributes, paths in attribute and derive macro invocations

This PR
 - refactors `Attribute` to use  `Path` and `TokenStream` instead of `MetaItem`.
 - supports macro invocation paths for attribute procedural macros.
   - e.g. `#[::foo::attr_macro] struct S;`, `#[cfg_attr(all(), foo::attr_macro)] struct S;`
 - supports macro invocation paths for derive procedural macros.
   - e.g. `#[derive(foo::Bar, super::Baz)] struct S;`
 - supports arbitrary tokens as arguments to attribute procedural macros.
   - e.g. `#[foo::attr_macro arbitrary + tokens] struct S;`
 - supports using arbitrary tokens in "inert attributes" with derive procedural macros.
   - e.g. `#[derive(Foo)] struct S(#[inert arbitrary + tokens] i32);`
where `#[proc_macro_derive(Foo, attributes(inert))]`

r? @nrc

1 files changed, 59 insertions, 41 deletions

diff --git a/src/libsyntax/print/pprust.rs b/src/libsyntax/print/pprust.rs
index 83753f398a3..f042a18d610 100644
--- a/src/libsyntax/print/pprust.rs
+++ b/src/libsyntax/print/pprust.rs
@@ -28,7 +28,7 @@ use ptr::P;
 use std_inject;
 use symbol::{Symbol, keywords};
 use syntax_pos::DUMMY_SP;
-use tokenstream::{self, TokenTree};
+use tokenstream::{self, TokenStream, TokenTree};
 
 use std::ascii;
 use std::io::{self, Write, Read};
@@ -329,6 +329,10 @@ pub fn tts_to_string(tts: &[tokenstream::TokenTree]) -> String {
     to_string(|s| s.print_tts(tts.iter().cloned().collect()))
 }
 
+pub fn tokens_to_string(tokens: TokenStream) -> String {
+    to_string(|s| s.print_tts(tokens))
+}
+
 pub fn stmt_to_string(stmt: &ast::Stmt) -> String {
     to_string(|s| s.print_stmt(stmt))
 }
@@ -750,7 +754,21 @@ pub trait PrintState<'a> {
                 ast::AttrStyle::Inner => word(self.writer(), "#![")?,
                 ast::AttrStyle::Outer => word(self.writer(), "#[")?,
             }
-            self.print_meta_item(&attr.meta())?;
+            if let Some(mi) = attr.meta() {
+                self.print_meta_item(&mi)?
+            } else {
+                for (i, segment) in attr.path.segments.iter().enumerate() {
+                    if i > 0 {
+                        word(self.writer(), "::")?
+                    }
+                    if segment.identifier.name != keywords::CrateRoot.name() &&
+                       segment.identifier.name != "$crate" {
+                        word(self.writer(), &segment.identifier.name.as_str())?;
+                    }
+                }
+                space(self.writer())?;
+                self.print_tts(attr.tokens.clone())?;
+            }
             word(self.writer(), "]")
         }
     }
@@ -789,6 +807,45 @@ pub trait PrintState<'a> {
         self.end()
     }
 
+    /// This doesn't deserve to be called "pretty" printing, but it should be
+    /// meaning-preserving. A quick hack that might help would be to look at the
+    /// spans embedded in the TTs to decide where to put spaces and newlines.
+    /// But it'd be better to parse these according to the grammar of the
+    /// appropriate macro, transcribe back into the grammar we just parsed from,
+    /// and then pretty-print the resulting AST nodes (so, e.g., we print
+    /// expression arguments as expressions). It can be done! I think.
+    fn print_tt(&mut self, tt: tokenstream::TokenTree) -> io::Result<()> {
+        match tt {
+            TokenTree::Token(_, ref tk) => {
+                word(self.writer(), &token_to_string(tk))?;
+                match *tk {
+                    parse::token::DocComment(..) => {
+                        hardbreak(self.writer())
+                    }
+                    _ => Ok(())
+                }
+            }
+            TokenTree::Delimited(_, ref delimed) => {
+                word(self.writer(), &token_to_string(&delimed.open_token()))?;
+                space(self.writer())?;
+                self.print_tts(delimed.stream())?;
+                space(self.writer())?;
+                word(self.writer(), &token_to_string(&delimed.close_token()))
+            },
+        }
+    }
+
+    fn print_tts(&mut self, tts: tokenstream::TokenStream) -> io::Result<()> {
+        self.ibox(0)?;
+        for (i, tt) in tts.into_trees().enumerate() {
+            if i != 0 {
+                space(self.writer())?;
+            }
+            self.print_tt(tt)?;
+        }
+        self.end()
+    }
+
     fn space_if_not_bol(&mut self) -> io::Result<()> {
         if !self.is_bol() { space(self.writer())?; }
         Ok(())
@@ -1458,45 +1515,6 @@ impl<'a> State<'a> {
         }
     }
 
-    /// This doesn't deserve to be called "pretty" printing, but it should be
-    /// meaning-preserving. A quick hack that might help would be to look at the
-    /// spans embedded in the TTs to decide where to put spaces and newlines.
-    /// But it'd be better to parse these according to the grammar of the
-    /// appropriate macro, transcribe back into the grammar we just parsed from,
-    /// and then pretty-print the resulting AST nodes (so, e.g., we print
-    /// expression arguments as expressions). It can be done! I think.
-    pub fn print_tt(&mut self, tt: tokenstream::TokenTree) -> io::Result<()> {
-        match tt {
-            TokenTree::Token(_, ref tk) => {
-                word(&mut self.s, &token_to_string(tk))?;
-                match *tk {
-                    parse::token::DocComment(..) => {
-                        hardbreak(&mut self.s)
-                    }
-                    _ => Ok(())
-                }
-            }
-            TokenTree::Delimited(_, ref delimed) => {
-                word(&mut self.s, &token_to_string(&delimed.open_token()))?;
-                space(&mut self.s)?;
-                self.print_tts(delimed.stream())?;
-                space(&mut self.s)?;
-                word(&mut self.s, &token_to_string(&delimed.close_token()))
-            },
-        }
-    }
-
-    pub fn print_tts(&mut self, tts: tokenstream::TokenStream) -> io::Result<()> {
-        self.ibox(0)?;
-        for (i, tt) in tts.into_trees().enumerate() {
-            if i != 0 {
-                space(&mut self.s)?;
-            }
-            self.print_tt(tt)?;
-        }
-        self.end()
-    }
-
     pub fn print_variant(&mut self, v: &ast::Variant) -> io::Result<()> {
         self.head("")?;
         let generics = ast::Generics::default();