Change Lit::tokens() to Lit::token_tree().

Because most of the call sites have an easier time working with a
`TokenTree` instead of a `TokenStream`.

src/libsyntax/attr/mod.rs

@@ -541,9 +541,10 @@ impl MetaItemKind {
         match *self {
             MetaItemKind::Word => TokenStream::default(),
             MetaItemKind::NameValue(ref lit) => {
-                let mut vec = vec![TokenTree::token(token::Eq, span).into()];
-                lit.tokens().append_to_tree_and_joint_vec(&mut vec);
-                TokenStream::new(vec)
+                TokenStream::new(vec![
+                    TokenTree::token(token::Eq, span).into(),
+                    lit.token_tree().into(),
+                ])
             }
             MetaItemKind::List(ref list) => {
                 let mut tokens = Vec::new();
@@ -606,7 +607,7 @@ impl NestedMetaItem {
     fn tokens(&self) -> TokenStream {
         match *self {
             NestedMetaItem::MetaItem(ref item) => item.tokens(),
-            NestedMetaItem::Literal(ref lit) => lit.tokens(),
+            NestedMetaItem::Literal(ref lit) => lit.token_tree().into(),
         }
     }
 

src/libsyntax/parse/literal.rs

@@ -3,7 +3,7 @@
 use crate::ast::{self, Lit, LitKind};
 use crate::parse::token::{self, Token};
 use crate::symbol::{kw, sym, Symbol};
-use crate::tokenstream::{TokenStream, TokenTree};
+use crate::tokenstream::TokenTree;
 
 use log::debug;
 use rustc_data_structures::sync::Lrc;
@@ -216,13 +216,13 @@ impl Lit {
         Lit { token: kind.to_lit_token(), kind, span }
     }
 
-    /// Losslessly convert an AST literal into a token stream.
-    crate fn tokens(&self) -> TokenStream {
+    /// Losslessly convert an AST literal into a token tree.
+    crate fn token_tree(&self) -> TokenTree {
         let token = match self.token.kind {
             token::Bool => token::Ident(self.token.symbol, false),
             _ => token::Literal(self.token),
         };
-        TokenTree::token(token, self.span).into()
+        TokenTree::token(token, self.span)
     }
 }
 

src/libsyntax/parse/parser/attr.rs

@@ -6,7 +6,6 @@ use crate::tokenstream::{TokenStream, TokenTree};
 use crate::source_map::Span;
 
 use log::debug;
-use smallvec::smallvec;
 
 #[derive(Debug)]
 enum InnerAttributeParsePolicy<'a> {
@@ -193,15 +192,15 @@ impl<'a> Parser<'a> {
                         is_interpolated_expr = true;
                     }
                 }
-                let tokens = if is_interpolated_expr {
+                let token_tree = if is_interpolated_expr {
                     // We need to accept arbitrary interpolated expressions to continue
                     // supporting things like `doc = $expr` that work on stable.
                     // Non-literal interpolated expressions are rejected after expansion.
-                    self.parse_token_tree().into()
+                    self.parse_token_tree()
                 } else {
-                    self.parse_unsuffixed_lit()?.tokens()
+                    self.parse_unsuffixed_lit()?.token_tree()
                 };
-                TokenStream::from_streams(smallvec![eq.into(), tokens])
+                TokenStream::new(vec![eq.into(), token_tree.into()])
             } else {
                 TokenStream::default()
             };