auto merge of #15834 : Kimundi/rust/moved_syntax_env, r=cmr

- Made custom syntax extensions capable of expanding custom macros by moving `SyntaxEnv` into `ExtCtx`
- Added convenience method on `ExtCtx` for getting a macro expander.
- Made a few things private to force only a single way to use them (through `ExtCtx`)
- Removed some ancient commented-out code

Closes #14946

Author: bors

src/libregex_macros/lib.rs

@@ -34,6 +34,7 @@ use syntax::ext::build::AstBuilder;
 use syntax::ext::base::{ExtCtxt, MacResult, MacExpr, DummyResult};
 use syntax::parse::token;
 use syntax::print::pprust;
+use syntax::fold::Folder;
 
 use rustc::plugin::Registry;
 
@@ -615,7 +616,7 @@ fn exec<'t>(which: ::regex::native::MatchKind, input: &'t str,
 /// Otherwise, logs an error with cx.span_err and returns None.
 fn parse(cx: &mut ExtCtxt, tts: &[ast::TokenTree]) -> Option<String> {
     let mut parser = cx.new_parser_from_tts(tts);
-    let entry = cx.expand_expr(parser.parse_expr());
+    let entry = cx.expander().fold_expr(parser.parse_expr());
     let regex = match entry.node {
         ast::ExprLit(lit) => {
             match lit.node {

src/libsyntax/ext/base.rs

@@ -20,9 +20,11 @@ use parse::token;
 use parse::token::{InternedString, intern, str_to_ident};
 use util::small_vector::SmallVector;
 use ext::mtwt;
+use fold::Folder;
 
 use std::collections::HashMap;
 use std::gc::{Gc, GC};
+use std::rc::Rc;
 
 // new-style macro! tt code:
 //
@@ -104,9 +106,9 @@ pub type IdentMacroExpanderFn =
 /// just into the compiler's internal macro table, for `make_def`).
 pub trait MacResult {
     /// Define a new macro.
-    // this particular flavor should go away; the idea that a macro might
-    // expand into either a macro definition or an expression, depending
-    // on what the context wants, is kind of silly.
+    // this should go away; the idea that a macro might expand into
+    // either a macro definition or an expression, depending on what
+    // the context wants, is kind of silly.
     fn make_def(&self) -> Option<MacroDef> {
         None
     }
@@ -314,7 +316,7 @@ impl BlockInfo {
 
 /// The base map of methods for expanding syntax extension
 /// AST nodes into full ASTs
-pub fn syntax_expander_table() -> SyntaxEnv {
+fn initial_syntax_expander_table() -> SyntaxEnv {
     // utility function to simplify creating NormalTT syntax extensions
     fn builtin_normal_expander(f: MacroExpanderFn) -> SyntaxExtension {
         NormalTT(box BasicMacroExpander {
@@ -431,7 +433,9 @@ pub struct ExtCtxt<'a> {
 
     pub mod_path: Vec<ast::Ident> ,
     pub trace_mac: bool,
-    pub exported_macros: Vec<Gc<ast::Item>>
+    pub exported_macros: Vec<Gc<ast::Item>>,
+
+    pub syntax_env: SyntaxEnv,
 }
 
 impl<'a> ExtCtxt<'a> {
@@ -445,22 +449,18 @@ impl<'a> ExtCtxt<'a> {
             ecfg: ecfg,
             trace_mac: false,
             exported_macros: Vec::new(),
+            syntax_env: initial_syntax_expander_table(),
         }
     }
 
-    pub fn expand_expr(&mut self, mut e: Gc<ast::Expr>) -> Gc<ast::Expr> {
-        loop {
-            match e.node {
-                ast::ExprMac(..) => {
-                    let mut expander = expand::MacroExpander {
-                        extsbox: syntax_expander_table(),
-                        cx: self,
-                    };
-                    e = expand::expand_expr(e, &mut expander);
-                }
-                _ => return e
-            }
-        }
+    #[deprecated = "Replaced with `expander().fold_expr()`"]
+    pub fn expand_expr(&mut self, e: Gc<ast::Expr>) -> Gc<ast::Expr> {
+        self.expander().fold_expr(e)
+    }
+
+    /// Returns a `Folder` for deeply expanding all macros in a AST node.
+    pub fn expander<'b>(&'b mut self) -> expand::MacroExpander<'b, 'a> {
+        expand::MacroExpander { cx: self }
     }
 
     pub fn new_parser_from_tts(&self, tts: &[ast::TokenTree])
@@ -570,7 +570,7 @@ impl<'a> ExtCtxt<'a> {
 pub fn expr_to_string(cx: &mut ExtCtxt, expr: Gc<ast::Expr>, err_msg: &str)
                    -> Option<(InternedString, ast::StrStyle)> {
     // we want to be able to handle e.g. concat("foo", "bar")
-    let expr = cx.expand_expr(expr);
+    let expr = cx.expander().fold_expr(expr);
     match expr.node {
         ast::ExprLit(l) => match l.node {
             ast::LitStr(ref s, style) => return Some(((*s).clone(), style)),
@@ -627,7 +627,7 @@ pub fn get_exprs_from_tts(cx: &mut ExtCtxt,
     let mut p = cx.new_parser_from_tts(tts);
     let mut es = Vec::new();
     while p.token != token::EOF {
-        es.push(cx.expand_expr(p.parse_expr()));
+        es.push(cx.expander().fold_expr(p.parse_expr()));
         if p.eat(&token::COMMA) {
             continue;
         }
@@ -642,10 +642,13 @@ pub fn get_exprs_from_tts(cx: &mut ExtCtxt,
 /// In order to have some notion of scoping for macros,
 /// we want to implement the notion of a transformation
 /// environment.
-
+///
 /// This environment maps Names to SyntaxExtensions.
+pub struct SyntaxEnv {
+    chain: Vec<MapChainFrame> ,
+}
 
-//impl question: how to implement it? Initially, the
+// impl question: how to implement it? Initially, the
 // env will contain only macros, so it might be painful
 // to add an empty frame for every context. Let's just
 // get it working, first....
@@ -657,15 +660,11 @@ pub fn get_exprs_from_tts(cx: &mut ExtCtxt,
 
 struct MapChainFrame {
     info: BlockInfo,
-    map: HashMap<Name, SyntaxExtension>,
-}
-
-pub struct SyntaxEnv {
-    chain: Vec<MapChainFrame> ,
+    map: HashMap<Name, Rc<SyntaxExtension>>,
 }
 
 impl SyntaxEnv {
-    pub fn new() -> SyntaxEnv {
+    fn new() -> SyntaxEnv {
         let mut map = SyntaxEnv { chain: Vec::new() };
         map.push_frame();
         map
@@ -692,18 +691,18 @@ impl SyntaxEnv {
         unreachable!()
     }
 
-    pub fn find<'a>(&'a self, k: &Name) -> Option<&'a SyntaxExtension> {
+    pub fn find(&self, k: &Name) -> Option<Rc<SyntaxExtension>> {
         for frame in self.chain.iter().rev() {
             match frame.map.find(k) {
-                Some(v) => return Some(v),
+                Some(v) => return Some(v.clone()),
                 None => {}
             }
         }
         None
     }
 
     pub fn insert(&mut self, k: Name, v: SyntaxExtension) {
-        self.find_escape_frame().map.insert(k, v);
+        self.find_escape_frame().map.insert(k, Rc::new(v));
     }
 
     pub fn info<'a>(&'a mut self) -> &'a mut BlockInfo {