Auto merge of #46895 - ricochet1k:macro-lifetimes, r=jseyfried

Allow lifetimes in macros

This is a resurrection of PR #41927 which was a resurrection of #33135, which is intended to fix #34303.

In short, this allows macros_rules! to use :lifetime as a matcher to match 'lifetimes.

Still to do:
- [x]  Feature gate

8 files changed, 69 insertions, 21 deletions

diff --git a/src/libsyntax/ext/quote.rs b/src/libsyntax/ext/quote.rs
index 6141c38ab14..59996d1e4a7 100644
--- a/src/libsyntax/ext/quote.rs
+++ b/src/libsyntax/ext/quote.rs
@@ -190,6 +190,12 @@ pub mod rt {
         }
     }
 
+    impl ToTokens for ast::Lifetime {
+        fn to_tokens(&self, _cx: &ExtCtxt) -> Vec<TokenTree> {
+            vec![TokenTree::Token(DUMMY_SP, token::Lifetime(self.ident))]
+        }
+    }
+
     macro_rules! impl_to_tokens_slice {
         ($t: ty, $sep: expr) => {
             impl ToTokens for [$t] {
diff --git a/src/libsyntax/ext/tt/macro_parser.rs b/src/libsyntax/ext/tt/macro_parser.rs
index 2167b64e610..124477620c2 100644
--- a/src/libsyntax/ext/tt/macro_parser.rs
+++ b/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(p.expect_lifetime()),
         // this is not supposed to happen, since it has been checked
         // when compiling the macro.
         _ => p.span_bug(sp, "invalid fragment specifier")
diff --git a/src/libsyntax/ext/tt/macro_rules.rs b/src/libsyntax/ext/tt/macro_rules.rs
index 5e58f003c2b..d86603e94e9 100644
--- a/src/libsyntax/ext/tt/macro_rules.rs
+++ b/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" => {
@@ -887,9 +888,21 @@ fn is_legal_fragment_specifier(sess: &ParseSess,
     match frag_name {
         "item" | "block" | "stmt" | "expr" | "pat" |
         "path" | "ty" | "ident" | "meta" | "tt" | "" => true,
+        "lifetime" => {
+            if !features.borrow().macro_lifetime_matcher &&
+               !attr::contains_name(attrs, "allow_internal_unstable") {
+                let explain = feature_gate::EXPLAIN_LIFETIME_MATCHER;
+                emit_feature_err(sess,
+                                 "macro_lifetime_matcher",
+                                 frag_span,
+                                 GateIssue::Language,
+                                 explain);
+            }
+            true
+        },
         "vis" => {
-            if     !features.borrow().macro_vis_matcher
-                && !attr::contains_name(attrs, "allow_internal_unstable") {
+            if !features.borrow().macro_vis_matcher &&
+               !attr::contains_name(attrs, "allow_internal_unstable") {
                 let explain = feature_gate::EXPLAIN_VIS_MATCHER;
                 emit_feature_err(sess,
                                  "macro_vis_matcher",
diff --git a/src/libsyntax/feature_gate.rs b/src/libsyntax/feature_gate.rs
index 7ae360678cd..c5de0da0979 100644
--- a/src/libsyntax/feature_gate.rs
+++ b/src/libsyntax/feature_gate.rs
@@ -447,6 +447,9 @@ declare_features! (
 
     // Termination trait in main (RFC 1937)
     (active, termination_trait, "1.24.0", Some(43301)),
+
+    // Allows use of the :lifetime macro fragment specifier
+    (active, macro_lifetime_matcher, "1.24.0", Some(46895)),
 );
 
 declare_features! (
@@ -1226,6 +1229,9 @@ pub const EXPLAIN_DERIVE_UNDERSCORE: &'static str =
 pub const EXPLAIN_VIS_MATCHER: &'static str =
     ":vis fragment specifier is experimental and subject to change";
 
+pub const EXPLAIN_LIFETIME_MATCHER: &'static str =
+    ":lifetime fragment specifier is experimental and subject to change";
+
 pub const EXPLAIN_PLACEMENT_IN: &'static str =
     "placement-in expression syntax is experimental and subject to change.";
 
diff --git a/src/libsyntax/fold.rs b/src/libsyntax/fold.rs
index 9916b74aeb3..6682a3439f1 100644
--- a/src/libsyntax/fold.rs
+++ b/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)),
     }
 }
 
diff --git a/src/libsyntax/parse/parser.rs b/src/libsyntax/parse/parser.rs
index 1a2146509e3..812e3c4967a 100644
--- a/src/libsyntax/parse/parser.rs
+++ b/src/libsyntax/parse/parser.rs
@@ -1295,6 +1295,10 @@ impl<'a> Parser<'a> {
     fn get_label(&mut self) -> ast::Ident {
         match self.token {
             token::Lifetime(ref ident) => *ident,
+            token::Interpolated(ref nt) => match nt.0 {
+                token::NtLifetime(lifetime) => lifetime.ident,
+                _ => self.bug("not a lifetime"),
+            },
             _ => self.bug("not a lifetime"),
         }
     }
@@ -2031,14 +2035,12 @@ impl<'a> Parser<'a> {
     }
 
     /// Parse single lifetime 'a or panic.
-    fn expect_lifetime(&mut self) -> Lifetime {
-        match self.token {
-            token::Lifetime(ident) => {
-                let ident_span = self.span;
-                self.bump();
-                Lifetime { ident: ident, span: ident_span, id: ast::DUMMY_NODE_ID }
-            }
-            _ => self.span_bug(self.span, "not a lifetime")
+    pub fn expect_lifetime(&mut self) -> Lifetime {
+        if let Some(lifetime) = self.token.lifetime(self.span) {
+            self.bump();
+            lifetime
+        } else {
+            self.span_bug(self.span, "not a lifetime")
         }
     }
 
diff --git a/src/libsyntax/parse/token.rs b/src/libsyntax/parse/token.rs
index 05368c52d2c..bd4f7f9853d 100644
--- a/src/libsyntax/parse/token.rs
+++ b/src/libsyntax/parse/token.rs
@@ -251,7 +251,7 @@ impl Token {
             Lt | BinOp(Shl)             | // associated path
             ModSep                      => true, // global path
             Interpolated(ref nt) => match nt.0 {
-                NtIdent(..) | NtTy(..) | NtPath(..) => true,
+                NtIdent(..) | NtTy(..) | NtPath(..) | NtLifetime(..) => true,
                 _ => false,
             },
             _ => false,
@@ -314,14 +314,26 @@ impl Token {
         false
     }
 
-    /// Returns `true` if the token is a lifetime.
-    pub fn is_lifetime(&self) -> bool {
+    /// Returns a lifetime with the span and a dummy id if it is a lifetime,
+    /// or the original lifetime if it is an interpolated lifetime, ignoring
+    /// the span.
+    pub fn lifetime(&self, span: Span) -> Option<ast::Lifetime> {
         match *self {
-            Lifetime(..) => true,
-            _            => false,
+            Lifetime(ident) =>
+                Some(ast::Lifetime { ident: ident, span: span, id: ast::DUMMY_NODE_ID }),
+            Interpolated(ref nt) => match nt.0 {
+                NtLifetime(lifetime) => Some(lifetime),
+                _ => None,
+            },
+            _ => None,
         }
     }
 
+    /// Returns `true` if the token is a lifetime.
+    pub fn is_lifetime(&self) -> bool {
+        self.lifetime(syntax_pos::DUMMY_SP).is_some()
+    }
+
     /// Returns `true` if the token is either the `mut` or `const` keyword.
     pub fn is_mutability(&self) -> bool {
         self.is_keyword(keywords::Mut) ||
@@ -486,6 +498,10 @@ impl Token {
                 let token = Token::Ident(ident.node);
                 tokens = Some(TokenTree::Token(ident.span, token).into());
             }
+            Nonterminal::NtLifetime(lifetime) => {
+                let token = Token::Lifetime(lifetime.ident);
+                tokens = Some(TokenTree::Token(lifetime.span, token).into());
+            }
             Nonterminal::NtTT(ref tt) => {
                 tokens = Some(tt.clone().into());
             }
@@ -524,6 +540,7 @@ pub enum Nonterminal {
     NtGenerics(ast::Generics),
     NtWhereClause(ast::WhereClause),
     NtArg(ast::Arg),
+    NtLifetime(ast::Lifetime),
 }
 
 impl fmt::Debug for Nonterminal {
@@ -546,6 +563,7 @@ impl fmt::Debug for Nonterminal {
             NtWhereClause(..) => f.pad("NtWhereClause(..)"),
             NtArg(..) => f.pad("NtArg(..)"),
             NtVis(..) => f.pad("NtVis(..)"),
+            NtLifetime(..) => f.pad("NtLifetime(..)"),
         }
     }
 }
diff --git a/src/libsyntax/print/pprust.rs b/src/libsyntax/print/pprust.rs
index 8f619e8af76..dd343a2384b 100644
--- a/src/libsyntax/print/pprust.rs
+++ b/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),
         }
     }
 }