Rollup merge of #22875 - kmcallister:maceager, r=sfackler

 MacEager is a MacResult implementation for the common case where you've already built each form of AST that you might return.

Fixes #17637. Based on #18814.

This is a [breaking-change] for syntax extensions:

  * MacExpr::new becomes MacEager::expr.

  * MacPat::new becomes MacEager::pat.

  * MacItems::new becomes MacEager::items. It takes a SmallVector directly,
    not an iterator.

r? @sfackler

10 files changed, 97 insertions, 74 deletions

diff --git a/src/libsyntax/diagnostics/plugin.rs b/src/libsyntax/diagnostics/plugin.rs
index b3afc3fc4dd..59fe3658437 100644
--- a/src/libsyntax/diagnostics/plugin.rs
+++ b/src/libsyntax/diagnostics/plugin.rs
@@ -14,10 +14,11 @@ use std::collections::BTreeMap;
 use ast;
 use ast::{Ident, Name, TokenTree};
 use codemap::Span;
-use ext::base::{ExtCtxt, MacExpr, MacResult, MacItems};
+use ext::base::{ExtCtxt, MacEager, MacResult};
 use ext::build::AstBuilder;
 use parse::token;
 use ptr::P;
+use util::small_vector::SmallVector;
 
 thread_local! {
     static REGISTERED_DIAGNOSTICS: RefCell<BTreeMap<Name, Option<Name>>> = {
@@ -73,7 +74,7 @@ pub fn expand_diagnostic_used<'cx>(ecx: &'cx mut ExtCtxt,
             ));
         }
     });
-    MacExpr::new(quote_expr!(ecx, ()))
+    MacEager::expr(quote_expr!(ecx, ()))
 }
 
 pub fn expand_register_diagnostic<'cx>(ecx: &'cx mut ExtCtxt,
@@ -101,7 +102,7 @@ pub fn expand_register_diagnostic<'cx>(ecx: &'cx mut ExtCtxt,
     let sym = Ident::new(token::gensym(&(
         "__register_diagnostic_".to_string() + &token::get_ident(*code)
     )));
-    MacItems::new(vec![quote_item!(ecx, mod $sym {}).unwrap()].into_iter())
+    MacEager::items(SmallVector::many(vec![quote_item!(ecx, mod $sym {}).unwrap()]))
 }
 
 pub fn expand_build_diagnostic_array<'cx>(ecx: &'cx mut ExtCtxt,
@@ -126,7 +127,7 @@ pub fn expand_build_diagnostic_array<'cx>(ecx: &'cx mut ExtCtxt,
             (descriptions.len(), ecx.expr_vec(span, descriptions))
         });
 
-    MacItems::new(vec![quote_item!(ecx,
+    MacEager::items(SmallVector::many(vec![quote_item!(ecx,
         pub static $name: [(&'static str, &'static str); $count] = $expr;
-    ).unwrap()].into_iter())
+    ).unwrap()]))
 }
diff --git a/src/libsyntax/ext/asm.rs b/src/libsyntax/ext/asm.rs
index 009bfef8623..ae48084947e 100644
--- a/src/libsyntax/ext/asm.rs
+++ b/src/libsyntax/ext/asm.rs
@@ -217,7 +217,7 @@ pub fn expand_asm<'cx>(cx: &'cx mut ExtCtxt, sp: Span, tts: &[ast::TokenTree])
         },
     });
 
-    MacExpr::new(P(ast::Expr {
+    MacEager::expr(P(ast::Expr {
         id: ast::DUMMY_NODE_ID,
         node: ast::ExprInlineAsm(ast::InlineAsm {
             asm: token::intern_and_get_ident(&asm),
diff --git a/src/libsyntax/ext/base.rs b/src/libsyntax/ext/base.rs
index 2ef90f04f75..e5d1fe2388c 100644
--- a/src/libsyntax/ext/base.rs
+++ b/src/libsyntax/ext/base.rs
@@ -28,6 +28,7 @@ use fold::Folder;
 
 use std::collections::HashMap;
 use std::rc::Rc;
+use std::default::Default;
 
 pub trait ItemDecorator {
     fn expand(&self,
@@ -226,9 +227,17 @@ impl<F> IdentMacroExpander for F
     }
 }
 
+// Use a macro because forwarding to a simple function has type system issues
+macro_rules! make_stmt_default {
+    ($me:expr) => {
+        $me.make_expr().map(|e| {
+            P(codemap::respan(e.span, ast::StmtExpr(e, ast::DUMMY_NODE_ID)))
+        })
+    }
+}
+
 /// The result of a macro expansion. The return values of the various
-/// methods are spliced into the AST at the callsite of the macro (or
-/// just into the compiler's internal macro table, for `make_def`).
+/// methods are spliced into the AST at the callsite of the macro.
 pub trait MacResult {
     /// Create an expression.
     fn make_expr(self: Box<Self>) -> Option<P<ast::Expr>> {
@@ -254,63 +263,76 @@ pub trait MacResult {
     /// By default this attempts to create an expression statement,
     /// returning None if that fails.
     fn make_stmt(self: Box<Self>) -> Option<P<ast::Stmt>> {
-        self.make_expr()
-            .map(|e| P(codemap::respan(e.span, ast::StmtExpr(e, ast::DUMMY_NODE_ID))))
+        make_stmt_default!(self)
     }
 }
 
-/// A convenience type for macros that return a single expression.
-pub struct MacExpr {
-    e: P<ast::Expr>
-}
-impl MacExpr {
-    pub fn new(e: P<ast::Expr>) -> Box<MacResult+'static> {
-        box MacExpr { e: e } as Box<MacResult+'static>
-    }
-}
-impl MacResult for MacExpr {
-    fn make_expr(self: Box<MacExpr>) -> Option<P<ast::Expr>> {
-        Some(self.e)
-    }
-    fn make_pat(self: Box<MacExpr>) -> Option<P<ast::Pat>> {
-        match self.e.node {
-            ast::ExprLit(_) => Some(P(ast::Pat {
-                id: ast::DUMMY_NODE_ID,
-                span: self.e.span,
-                node: ast::PatLit(self.e)
-            })),
-            _ => None
+macro_rules! make_MacEager {
+    ( $( $fld:ident: $t:ty, )* ) => {
+        /// `MacResult` implementation for the common case where you've already
+        /// built each form of AST that you might return.
+        #[derive(Default)]
+        pub struct MacEager {
+            $(
+                pub $fld: Option<$t>,
+            )*
+        }
+
+        impl MacEager {
+            $(
+                pub fn $fld(v: $t) -> Box<MacResult> {
+                    box MacEager {
+                        $fld: Some(v),
+                        ..Default::default()
+                    } as Box<MacResult>
+                }
+            )*
         }
     }
 }
-/// A convenience type for macros that return a single pattern.
-pub struct MacPat {
-    p: P<ast::Pat>
+
+make_MacEager! {
+    expr: P<ast::Expr>,
+    pat: P<ast::Pat>,
+    items: SmallVector<P<ast::Item>>,
+    methods: SmallVector<P<ast::Method>>,
+    stmt: P<ast::Stmt>,
 }
-impl MacPat {
-    pub fn new(p: P<ast::Pat>) -> Box<MacResult+'static> {
-        box MacPat { p: p } as Box<MacResult+'static>
+
+impl MacResult for MacEager {
+    fn make_expr(self: Box<Self>) -> Option<P<ast::Expr>> {
+        self.expr
     }
-}
-impl MacResult for MacPat {
-    fn make_pat(self: Box<MacPat>) -> Option<P<ast::Pat>> {
-        Some(self.p)
+
+    fn make_items(self: Box<Self>) -> Option<SmallVector<P<ast::Item>>> {
+        self.items
     }
-}
-/// A type for macros that return multiple items.
-pub struct MacItems {
-    items: SmallVector<P<ast::Item>>
-}
 
-impl MacItems {
-    pub fn new<I: Iterator<Item=P<ast::Item>>>(it: I) -> Box<MacResult+'static> {
-        box MacItems { items: it.collect() } as Box<MacResult+'static>
+    fn make_methods(self: Box<Self>) -> Option<SmallVector<P<ast::Method>>> {
+        self.methods
     }
-}
 
-impl MacResult for MacItems {
-    fn make_items(self: Box<MacItems>) -> Option<SmallVector<P<ast::Item>>> {
-        Some(self.items)
+    fn make_stmt(self: Box<Self>) -> Option<P<ast::Stmt>> {
+        match self.stmt {
+            None => make_stmt_default!(self),
+            s => s,
+        }
+    }
+
+    fn make_pat(self: Box<Self>) -> Option<P<ast::Pat>> {
+        if let Some(p) = self.pat {
+            return Some(p);
+        }
+        if let Some(e) = self.expr {
+            if let ast::ExprLit(_) = e.node {
+                return Some(P(ast::Pat {
+                    id: ast::DUMMY_NODE_ID,
+                    span: e.span,
+                    node: ast::PatLit(e),
+                }));
+            }
+        }
+        None
     }
 }
 
diff --git a/src/libsyntax/ext/cfg.rs b/src/libsyntax/ext/cfg.rs
index 7216602071b..6a2209bf0ae 100644
--- a/src/libsyntax/ext/cfg.rs
+++ b/src/libsyntax/ext/cfg.rs
@@ -35,5 +35,5 @@ pub fn expand_cfg<'cx>(cx: &mut ExtCtxt,
     }
 
     let matches_cfg = attr::cfg_matches(&cx.parse_sess.span_diagnostic, &cx.cfg, &*cfg);
-    MacExpr::new(cx.expr_bool(sp, matches_cfg))
+    MacEager::expr(cx.expr_bool(sp, matches_cfg))
 }
diff --git a/src/libsyntax/ext/concat.rs b/src/libsyntax/ext/concat.rs
index 84f786e9780..754c73a9d78 100644
--- a/src/libsyntax/ext/concat.rs
+++ b/src/libsyntax/ext/concat.rs
@@ -60,7 +60,7 @@ pub fn expand_syntax_ext(cx: &mut base::ExtCtxt,
             }
         }
     }
-    base::MacExpr::new(cx.expr_str(
+    base::MacEager::expr(cx.expr_str(
             sp,
             token::intern_and_get_ident(&accumulator[..])))
 }
diff --git a/src/libsyntax/ext/concat_idents.rs b/src/libsyntax/ext/concat_idents.rs
index 2303eb9645b..e350ce61017 100644
--- a/src/libsyntax/ext/concat_idents.rs
+++ b/src/libsyntax/ext/concat_idents.rs
@@ -67,5 +67,5 @@ pub fn expand_syntax_ext<'cx>(cx: &mut ExtCtxt, sp: Span, tts: &[ast::TokenTree]
         ),
         span: sp,
     });
-    MacExpr::new(e)
+    MacEager::expr(e)
 }
diff --git a/src/libsyntax/ext/env.rs b/src/libsyntax/ext/env.rs
index 93f8ee5042b..f72303985e7 100644
--- a/src/libsyntax/ext/env.rs
+++ b/src/libsyntax/ext/env.rs
@@ -59,7 +59,7 @@ pub fn expand_option_env<'cx>(cx: &'cx mut ExtCtxt, sp: Span, tts: &[ast::TokenT
                                           &s[..]))))
       }
     };
-    MacExpr::new(e)
+    MacEager::expr(e)
 }
 
 pub fn expand_env<'cx>(cx: &'cx mut ExtCtxt, sp: Span, tts: &[ast::TokenTree])
@@ -108,5 +108,5 @@ pub fn expand_env<'cx>(cx: &'cx mut ExtCtxt, sp: Span, tts: &[ast::TokenTree])
         }
         Ok(s) => cx.expr_str(sp, token::intern_and_get_ident(&s))
     };
-    MacExpr::new(e)
+    MacEager::expr(e)
 }
diff --git a/src/libsyntax/ext/format.rs b/src/libsyntax/ext/format.rs
index 91262556abd..0eaca9af4f0 100644
--- a/src/libsyntax/ext/format.rs
+++ b/src/libsyntax/ext/format.rs
@@ -633,7 +633,7 @@ pub fn expand_format_args<'cx>(ecx: &'cx mut ExtCtxt, sp: Span,
 
     match parse_args(ecx, sp, tts) {
         Some((efmt, args, order, names)) => {
-            MacExpr::new(expand_preparsed_format_args(ecx, sp, efmt,
+            MacEager::expr(expand_preparsed_format_args(ecx, sp, efmt,
                                                       args, order, names))
         }
         None => DummyResult::expr(sp)
diff --git a/src/libsyntax/ext/quote.rs b/src/libsyntax/ext/quote.rs
index 554529b5cb2..544fb15dcde 100644
--- a/src/libsyntax/ext/quote.rs
+++ b/src/libsyntax/ext/quote.rs
@@ -402,7 +402,7 @@ pub fn expand_quote_tokens<'cx>(cx: &'cx mut ExtCtxt,
                                 -> Box<base::MacResult+'cx> {
     let (cx_expr, expr) = expand_tts(cx, sp, tts);
     let expanded = expand_wrapper(cx, sp, cx_expr, expr);
-    base::MacExpr::new(expanded)
+    base::MacEager::expr(expanded)
 }
 
 pub fn expand_quote_expr<'cx>(cx: &'cx mut ExtCtxt,
@@ -410,7 +410,7 @@ pub fn expand_quote_expr<'cx>(cx: &'cx mut ExtCtxt,
                               tts: &[ast::TokenTree])
                               -> Box<base::MacResult+'cx> {
     let expanded = expand_parse_call(cx, sp, "parse_expr", Vec::new(), tts);
-    base::MacExpr::new(expanded)
+    base::MacEager::expr(expanded)
 }
 
 pub fn expand_quote_item<'cx>(cx: &mut ExtCtxt,
@@ -419,7 +419,7 @@ pub fn expand_quote_item<'cx>(cx: &mut ExtCtxt,
                               -> Box<base::MacResult+'cx> {
     let expanded = expand_parse_call(cx, sp, "parse_item_with_outer_attributes",
                                     vec!(), tts);
-    base::MacExpr::new(expanded)
+    base::MacEager::expr(expanded)
 }
 
 pub fn expand_quote_pat<'cx>(cx: &'cx mut ExtCtxt,
@@ -427,7 +427,7 @@ pub fn expand_quote_pat<'cx>(cx: &'cx mut ExtCtxt,
                              tts: &[ast::TokenTree])
                              -> Box<base::MacResult+'cx> {
     let expanded = expand_parse_call(cx, sp, "parse_pat", vec!(), tts);
-    base::MacExpr::new(expanded)
+    base::MacEager::expr(expanded)
 }
 
 pub fn expand_quote_arm(cx: &mut ExtCtxt,
@@ -435,7 +435,7 @@ pub fn expand_quote_arm(cx: &mut ExtCtxt,
                         tts: &[ast::TokenTree])
                         -> Box<base::MacResult+'static> {
     let expanded = expand_parse_call(cx, sp, "parse_arm", vec!(), tts);
-    base::MacExpr::new(expanded)
+    base::MacEager::expr(expanded)
 }
 
 pub fn expand_quote_ty(cx: &mut ExtCtxt,
@@ -443,7 +443,7 @@ pub fn expand_quote_ty(cx: &mut ExtCtxt,
                        tts: &[ast::TokenTree])
                        -> Box<base::MacResult+'static> {
     let expanded = expand_parse_call(cx, sp, "parse_ty", vec!(), tts);
-    base::MacExpr::new(expanded)
+    base::MacEager::expr(expanded)
 }
 
 pub fn expand_quote_method(cx: &mut ExtCtxt,
@@ -452,7 +452,7 @@ pub fn expand_quote_method(cx: &mut ExtCtxt,
                            -> Box<base::MacResult+'static> {
     let expanded = expand_parse_call(cx, sp, "parse_method_with_outer_attributes",
                                      vec!(), tts);
-    base::MacExpr::new(expanded)
+    base::MacEager::expr(expanded)
 }
 
 pub fn expand_quote_stmt(cx: &mut ExtCtxt,
@@ -462,7 +462,7 @@ pub fn expand_quote_stmt(cx: &mut ExtCtxt,
     let e_attrs = cx.expr_vec_ng(sp);
     let expanded = expand_parse_call(cx, sp, "parse_stmt",
                                     vec!(e_attrs), tts);
-    base::MacExpr::new(expanded)
+    base::MacEager::expr(expanded)
 }
 
 fn ids_ext(strs: Vec<String> ) -> Vec<ast::Ident> {
diff --git a/src/libsyntax/ext/source_util.rs b/src/libsyntax/ext/source_util.rs
index af43f5a1501..ba3743cdb33 100644
--- a/src/libsyntax/ext/source_util.rs
+++ b/src/libsyntax/ext/source_util.rs
@@ -35,7 +35,7 @@ pub fn expand_line(cx: &mut ExtCtxt, sp: Span, tts: &[ast::TokenTree])
     let topmost = cx.original_span_in_file();
     let loc = cx.codemap().lookup_char_pos(topmost.lo);
 
-    base::MacExpr::new(cx.expr_u32(topmost, loc.line as u32))
+    base::MacEager::expr(cx.expr_u32(topmost, loc.line as u32))
 }
 
 /* column!(): expands to the current column number */
@@ -46,7 +46,7 @@ pub fn expand_column(cx: &mut ExtCtxt, sp: Span, tts: &[ast::TokenTree])
     let topmost = cx.original_span_in_file();
     let loc = cx.codemap().lookup_char_pos(topmost.lo);
 
-    base::MacExpr::new(cx.expr_u32(topmost, loc.col.to_usize() as u32))
+    base::MacEager::expr(cx.expr_u32(topmost, loc.col.to_usize() as u32))
 }
 
 /// file!(): expands to the current filename */
@@ -59,13 +59,13 @@ pub fn expand_file(cx: &mut ExtCtxt, sp: Span, tts: &[ast::TokenTree])
     let topmost = cx.original_span_in_file();
     let loc = cx.codemap().lookup_char_pos(topmost.lo);
     let filename = token::intern_and_get_ident(&loc.file.name);
-    base::MacExpr::new(cx.expr_str(topmost, filename))
+    base::MacEager::expr(cx.expr_str(topmost, filename))
 }
 
 pub fn expand_stringify(cx: &mut ExtCtxt, sp: Span, tts: &[ast::TokenTree])
                         -> Box<base::MacResult+'static> {
     let s = pprust::tts_to_string(tts);
-    base::MacExpr::new(cx.expr_str(sp,
+    base::MacEager::expr(cx.expr_str(sp,
                                    token::intern_and_get_ident(&s[..])))
 }
 
@@ -77,7 +77,7 @@ pub fn expand_mod(cx: &mut ExtCtxt, sp: Span, tts: &[ast::TokenTree])
                    .map(|x| token::get_ident(*x).to_string())
                    .collect::<Vec<String>>()
                    .connect("::");
-    base::MacExpr::new(cx.expr_str(
+    base::MacEager::expr(cx.expr_str(
             sp,
             token::intern_and_get_ident(&string[..])))
 }
@@ -155,7 +155,7 @@ pub fn expand_include_str(cx: &mut ExtCtxt, sp: Span, tts: &[ast::TokenTree])
             let interned = token::intern_and_get_ident(&src[..]);
             cx.codemap().new_filemap(filename, src);
 
-            base::MacExpr::new(cx.expr_str(sp, interned))
+            base::MacEager::expr(cx.expr_str(sp, interned))
         }
         Err(_) => {
             cx.span_err(sp,
@@ -181,7 +181,7 @@ pub fn expand_include_bytes(cx: &mut ExtCtxt, sp: Span, tts: &[ast::TokenTree])
         }
         Ok(bytes) => {
             let bytes = bytes.iter().cloned().collect();
-            base::MacExpr::new(cx.expr_lit(sp, ast::LitBinary(Rc::new(bytes))))
+            base::MacEager::expr(cx.expr_lit(sp, ast::LitBinary(Rc::new(bytes))))
         }
     }
 }