Auto merge of #29780 - KyleMayes:quote-ext, r=nrc

This is my first code contribution to Rust, so I'm sure there are some issues with the changes I've made.

I've added the `quote_arg!`, `quote_block!`, `quote_path!`, and `quote_meta_item!` quasiquoting macros. From my experience trying to build AST in compiler plugins, I would like to be able to build any AST piece with a quasiquoting macro (e.g., `quote_struct_field!` or `quote_variant!`) and then use those AST pieces in other quasiquoting macros, but this pull request just adds some of the low-hanging fruit.

I'm not sure if these additions are desirable, and I'm sure these macros can be implemented in an external crate if not.

src/libsyntax/ext/base.rs

@@ -512,6 +512,18 @@ fn initial_syntax_expander_table<'feat>(ecfg: &expand::ExpansionConfig<'feat>)
         syntax_expanders.insert(intern("quote_attr"),
                            builtin_normal_expander(
                                 ext::quote::expand_quote_attr));
+        syntax_expanders.insert(intern("quote_arg"),
+                           builtin_normal_expander(
+                                ext::quote::expand_quote_arg));
+        syntax_expanders.insert(intern("quote_block"),
+                           builtin_normal_expander(
+                                ext::quote::expand_quote_block));
+        syntax_expanders.insert(intern("quote_meta_item"),
+                           builtin_normal_expander(
+                                ext::quote::expand_quote_meta_item));
+        syntax_expanders.insert(intern("quote_path"),
+                           builtin_normal_expander(
+                                ext::quote::expand_quote_path));
     }
 
     syntax_expanders.insert(intern("line"),

src/libsyntax/ext/quote.rs

@@ -158,6 +158,18 @@ pub mod rt {
         }
     }
 
+    impl ToTokens for ast::Arg {
+        fn to_tokens(&self, _cx: &ExtCtxt) -> Vec<TokenTree> {
+            vec![TokenTree::Token(DUMMY_SP, token::Interpolated(token::NtArg(self.clone())))]
+        }
+    }
+
+    impl ToTokens for P<ast::Block> {
+        fn to_tokens(&self, _cx: &ExtCtxt) -> Vec<TokenTree> {
+            vec![TokenTree::Token(DUMMY_SP, token::Interpolated(token::NtBlock(self.clone())))]
+        }
+    }
+
     macro_rules! impl_to_tokens_slice {
         ($t: ty, $sep: expr) => {
             impl ToTokens for [$t] {
@@ -177,6 +189,7 @@ pub mod rt {
 
     impl_to_tokens_slice! { ast::Ty, [TokenTree::Token(DUMMY_SP, token::Comma)] }
     impl_to_tokens_slice! { P<ast::Item>, [] }
+    impl_to_tokens_slice! { ast::Arg, [TokenTree::Token(DUMMY_SP, token::Comma)] }
 
     impl ToTokens for P<ast::MetaItem> {
         fn to_tokens(&self, _cx: &ExtCtxt) -> Vec<TokenTree> {
@@ -383,6 +396,39 @@ pub fn expand_quote_attr(cx: &mut ExtCtxt,
     base::MacEager::expr(expanded)
 }
 
+pub fn expand_quote_arg(cx: &mut ExtCtxt,
+                        sp: Span,
+                        tts: &[TokenTree])
+                        -> Box<base::MacResult+'static> {
+    let expanded = expand_parse_call(cx, sp, "parse_arg_panic", vec!(), tts);
+    base::MacEager::expr(expanded)
+}
+
+pub fn expand_quote_block(cx: &mut ExtCtxt,
+                        sp: Span,
+                        tts: &[TokenTree])
+                        -> Box<base::MacResult+'static> {
+    let expanded = expand_parse_call(cx, sp, "parse_block_panic", vec!(), tts);
+    base::MacEager::expr(expanded)
+}
+
+pub fn expand_quote_meta_item(cx: &mut ExtCtxt,
+                        sp: Span,
+                        tts: &[TokenTree])
+                        -> Box<base::MacResult+'static> {
+    let expanded = expand_parse_call(cx, sp, "parse_meta_item_panic", vec!(), tts);
+    base::MacEager::expr(expanded)
+}
+
+pub fn expand_quote_path(cx: &mut ExtCtxt,
+                        sp: Span,
+                        tts: &[TokenTree])
+                        -> Box<base::MacResult+'static> {
+    let mode = mk_parser_path(cx, sp, "LifetimeAndTypesWithoutColons");
+    let expanded = expand_parse_call(cx, sp, "parse_path_panic", vec!(mode), tts);
+    base::MacEager::expr(expanded)
+}
+
 pub fn expand_quote_matcher(cx: &mut ExtCtxt,
                             sp: Span,
                             tts: &[TokenTree])
@@ -440,6 +486,11 @@ fn mk_token_path(cx: &ExtCtxt, sp: Span, name: &str) -> P<ast::Expr> {
     cx.expr_path(cx.path_global(sp, idents))
 }
 
+fn mk_parser_path(cx: &ExtCtxt, sp: Span, name: &str) -> P<ast::Expr> {
+    let idents = vec!(id_ext("syntax"), id_ext("parse"), id_ext("parser"), id_ext(name));
+    cx.expr_path(cx.path_global(sp, idents))
+}
+
 fn mk_binop(cx: &ExtCtxt, sp: Span, bop: token::BinOpToken) -> P<ast::Expr> {
     let name = match bop {
         token::Plus     => "Plus",