Resurrecting #33135

Started rebasing @sgrif's PR #33135 off of current master. (Well, actually merging it into a new branch based off current master.)

The following files still need to be fixed or at least reviewed:

- `src/libsyntax/ext/tt/macro_parser.rs`: calls `Parser::parse_lifetime`, which doesn't exist anymore
- `src/libsyntax/parse/parser.rs`: @sgrif added an error message to `Parser::parse_lifetime`. Code has since been refactored, so I just took it out for now.
- `src/libsyntax/ext/tt/transcribe.rs`: This code has been refactored bigtime. Not sure whether @sgrif's changes here are still necessary. Took it out for this commit.

src/libsyntax/ext/quote.rs

@@ -190,6 +190,13 @@ pub mod rt {
         }
     }
 
+    impl ToTokens for ast::Lifetime {
+        fn to_tokens(&self, _cx: &ExtCtxt) -> Vec<TokenTree> {
+            let lifetime_ident = ast::Ident::with_empty_ctxt(self.name);
+            vec![TokenTree::Token(DUMMY_SP, token::Lifetime(lifetime_ident))]
+        }
+    }
+
     macro_rules! impl_to_tokens_slice {
         ($t: ty, $sep: expr) => {
             impl ToTokens for [$t] {

src/libsyntax/ext/tt/macro_parser.rs

@@ -603,6 +603,7 @@ fn parse_nt<'a>(p: &mut Parser<'a>, sp: Span, name: &str) -> Nonterminal {
         "path" => token::NtPath(panictry!(p.parse_path_common(PathStyle::Type, false))),
         "meta" => token::NtMeta(panictry!(p.parse_meta_item())),
         "vis" => token::NtVis(panictry!(p.parse_visibility(true))),
+        "lifetime" => token::NtLifetime(panictry!(p.parse_lifetime())),
         // this is not supposed to happen, since it has been checked
         // when compiling the macro.
         _ => p.span_bug(sp, "invalid fragment specifier")

src/libsyntax/ext/tt/macro_rules.rs

@@ -768,10 +768,11 @@ fn token_can_be_followed_by_any(tok: &quoted::TokenTree) -> bool {
 /// ANYTHING without fear of future compatibility hazards).
 fn frag_can_be_followed_by_any(frag: &str) -> bool {
     match frag {
-        "item"  | // always terminated by `}` or `;`
-        "block" | // exactly one token tree
-        "ident" | // exactly one token tree
-        "meta"  | // exactly one token tree
+        "item"     | // always terminated by `}` or `;`
+        "block"    | // exactly one token tree
+        "ident"    | // exactly one token tree
+        "meta"     | // exactly one token tree
+        "lifetime" | // exactly one token tree
         "tt" =>   // exactly one token tree
             true,
 
@@ -832,8 +833,8 @@ fn is_in_follow(tok: &quoted::TokenTree, frag: &str) -> Result<bool, (String, &'
                 TokenTree::MetaVarDecl(_, _, frag) if frag.name == "block" => Ok(true),
                 _ => Ok(false),
             },
-            "ident" => {
-                // being a single token, idents are harmless
+            "ident" | "lifetime" => {
+                // being a single token, idents and lifetimes are harmless
                 Ok(true)
             },
             "meta" | "tt" => {
@@ -885,7 +886,7 @@ fn is_legal_fragment_specifier(sess: &ParseSess,
                                frag_name: &str,
                                frag_span: Span) -> bool {
     match frag_name {
-        "item" | "block" | "stmt" | "expr" | "pat" |
+        "item" | "block" | "stmt" | "expr" | "pat" | "lifetime" |
         "path" | "ty" | "ident" | "meta" | "tt" | "" => true,
         "vis" => {
             if     !features.borrow().macro_vis_matcher

src/libsyntax/fold.rs

@@ -642,6 +642,7 @@ pub fn noop_fold_interpolated<T: Folder>(nt: token::Nonterminal, fld: &mut T)
             token::NtWhereClause(fld.fold_where_clause(where_clause)),
         token::NtArg(arg) => token::NtArg(fld.fold_arg(arg)),
         token::NtVis(vis) => token::NtVis(fld.fold_vis(vis)),
+        token::NtLifetime(lifetime) => token::NtLifetime(fld.fold_lifetime(lifetime)),
     }
 }
 

src/libsyntax/parse/token.rs

@@ -524,6 +524,7 @@ pub enum Nonterminal {
     NtGenerics(ast::Generics),
     NtWhereClause(ast::WhereClause),
     NtArg(ast::Arg),
+    NtLifetime(ast::Lifetime),
 }
 
 impl fmt::Debug for Nonterminal {
@@ -546,6 +547,7 @@ impl fmt::Debug for Nonterminal {
             NtWhereClause(..) => f.pad("NtWhereClause(..)"),
             NtArg(..) => f.pad("NtArg(..)"),
             NtVis(..) => f.pad("NtVis(..)"),
+            NtLifetime(..) => f.pad("NtLifetime(..)"),
         }
     }
 }

src/libsyntax/print/pprust.rs

@@ -279,6 +279,7 @@ pub fn token_to_string(tok: &Token) -> String {
             token::NtWhereClause(ref e) => where_clause_to_string(e),
             token::NtArg(ref e)         => arg_to_string(e),
             token::NtVis(ref e)         => vis_to_string(e),
+            token::NtLifetime(ref e)    => lifetime_to_string(e),
         }
     }
 }

src/test/run-pass/macro-lifetime-used-with-bound.rs

@@ -0,0 +1,23 @@
+// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+macro_rules! foo {
+    ($l:lifetime, $l2:lifetime) => {
+        fn f<$l: $l2, $l2>(arg: &$l str, arg2: &$l2 str) -> &$l str {
+            arg
+        }
+    }
+}
+
+pub fn main() {
+    foo!('a, 'b);
+    let x: &'static str = f("hi", "there");
+    assert_eq!("hi", x);
+}

src/test/run-pass/macro-lifetime-used-with-static.rs

@@ -0,0 +1,23 @@
+// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+macro_rules! foo {
+    ($l:lifetime) => {
+        fn f(arg: &$l str) -> &$l str {
+            arg
+        }
+    }
+}
+
+pub fn main() {
+    foo!('static);
+    let x: &'static str = f("hi");
+    assert_eq!("hi", x);
+}

src/test/run-pass/macro-lifetime.rs

@@ -0,0 +1,23 @@
+// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+macro_rules! foo {
+    ($l:lifetime) => {
+        fn f<$l>(arg: &$l str) -> &$l str {
+            arg
+        }
+    }
+}
+
+pub fn main() {
+    foo!('a);
+    let x: &'static str = f("hi");
+    assert_eq!("hi", x);
+}