auto merge of #10649 : sfackler/rust/multi-macro, r=alexcrichton

The majority of this change is modifying some of the `ast_visit` methods to return multiple values.

It's prohibitively expensive to allocate a `~[Foo]` every time a statement, declaration, item, etc is visited, especially since the vast majority will have 0 or 1 elements. I've added a `SmallVector` class that avoids allocation in the 0 and 1 element cases to take care of that.

Author: bors

src/librustc/front/config.rs

@@ -48,14 +48,6 @@ pub fn strip_items(crate: ast::Crate,
     ctxt.fold_crate(crate)
 }
 
-fn filter_item(cx: &Context, item: @ast::item) -> Option<@ast::item> {
-    if item_in_cfg(cx, item) {
-        Some(item)
-    } else {
-        None
-    }
-}
-
 fn filter_view_item<'r>(cx: &Context, view_item: &'r ast::view_item)
                         -> Option<&'r ast::view_item> {
     if view_item_in_cfg(cx, view_item) {
@@ -66,9 +58,10 @@ fn filter_view_item<'r>(cx: &Context, view_item: &'r ast::view_item)
 }
 
 fn fold_mod(cx: &Context, m: &ast::_mod) -> ast::_mod {
-    let filtered_items = m.items.iter().filter_map(|a| {
-        filter_item(cx, *a).and_then(|x| cx.fold_item(x))
-    }).collect();
+    let filtered_items = m.items.iter()
+            .filter(|&a| item_in_cfg(cx, *a))
+            .flat_map(|&x| cx.fold_item(x).move_iter())
+            .collect();
     let filtered_view_items = m.view_items.iter().filter_map(|a| {
         filter_view_item(cx, a).map(|x| cx.fold_view_item(x))
     }).collect();
@@ -122,28 +115,25 @@ fn fold_item_underscore(cx: &Context, item: &ast::item_) -> ast::item_ {
     fold::noop_fold_item_underscore(&item, cx)
 }
 
-fn filter_stmt(cx: &Context, stmt: @ast::Stmt) -> Option<@ast::Stmt> {
+fn retain_stmt(cx: &Context, stmt: @ast::Stmt) -> bool {
     match stmt.node {
       ast::StmtDecl(decl, _) => {
         match decl.node {
           ast::DeclItem(item) => {
-            if item_in_cfg(cx, item) {
-                Some(stmt)
-            } else {
-                None
-            }
+            item_in_cfg(cx, item)
           }
-          _ => Some(stmt)
+          _ => true
         }
       }
-      _ => Some(stmt),
+      _ => true
     }
 }
 
 fn fold_block(cx: &Context, b: &ast::Block) -> ast::Block {
-    let resulting_stmts = b.stmts.iter().filter_map(|a| {
-        filter_stmt(cx, *a).and_then(|stmt| cx.fold_stmt(stmt))
-    }).collect();
+    let resulting_stmts = b.stmts.iter()
+            .filter(|&a| retain_stmt(cx, *a))
+            .flat_map(|&stmt| cx.fold_stmt(stmt).move_iter())
+            .collect();
     let filtered_view_items = b.view_items.iter().filter_map(|a| {
         filter_view_item(cx, a).map(|x| cx.fold_view_item(x))
     }).collect();

src/librustc/front/std_inject.rs

@@ -19,6 +19,7 @@ use syntax::codemap;
 use syntax::fold::ast_fold;
 use syntax::fold;
 use syntax::opt_vec;
+use syntax::util::small_vector::SmallVector;
 
 static STD_VERSION: &'static str = "0.9-pre";
 
@@ -98,14 +99,14 @@ impl fold::ast_fold for StandardLibraryInjector {
         }
     }
 
-    fn fold_item(&self, item: @ast::item) -> Option<@ast::item> {
+    fn fold_item(&self, item: @ast::item) -> SmallVector<@ast::item> {
         if !no_prelude(item.attrs) {
             // only recur if there wasn't `#[no_implicit_prelude];`
             // on this item, i.e. this means that the prelude is not
             // implicitly imported though the whole subtree
             fold::noop_fold_item(item, self)
         } else {
-            Some(item)
+            SmallVector::one(item)
         }
     }
 

src/librustc/front/test.rs

@@ -26,6 +26,7 @@ use syntax::fold;
 use syntax::opt_vec;
 use syntax::print::pprust;
 use syntax::{ast, ast_util};
+use syntax::util::small_vector::SmallVector;
 
 struct Test {
     span: Span,
@@ -76,7 +77,7 @@ impl fold::ast_fold for TestHarnessGenerator {
         }
     }
 
-    fn fold_item(&self, i: @ast::item) -> Option<@ast::item> {
+    fn fold_item(&self, i: @ast::item) -> SmallVector<@ast::item> {
         self.cx.path.push(i.ident);
         debug!("current path: {}",
                ast_util::path_name_i(self.cx.path.clone()));
@@ -108,7 +109,7 @@ impl fold::ast_fold for TestHarnessGenerator {
 
         let res = fold::noop_fold_item(i, self);
         self.cx.path.pop();
-        return res;
+        res
     }
 
     fn fold_mod(&self, m: &ast::_mod) -> ast::_mod {

src/librustc/middle/astencode.rs

@@ -347,7 +347,8 @@ fn simplify_ast(ii: &ast::inlined_item) -> ast::inlined_item {
 
     match *ii {
         //hack: we're not dropping items
-        ast::ii_item(i) => ast::ii_item(fld.fold_item(i).unwrap()),
+        ast::ii_item(i) => ast::ii_item(fld.fold_item(i)
+                                        .expect_one("expected one item")),
         ast::ii_method(d, is_provided, m) =>
           ast::ii_method(d, is_provided, fld.fold_method(m)),
         ast::ii_foreign(i) => ast::ii_foreign(fld.fold_foreign_item(i))
@@ -379,7 +380,8 @@ fn renumber_ast(xcx: @ExtendedDecodeContext, ii: ast::inlined_item)
         xcx: xcx,
     };
     match ii {
-        ast::ii_item(i) => ast::ii_item(fld.fold_item(i).unwrap()),
+        ast::ii_item(i) => ast::ii_item(fld.fold_item(i)
+                                        .expect_one("expected one item")),
         ast::ii_method(d, is_provided, m) =>
           ast::ii_method(xcx.tr_def_id(d), is_provided, fld.fold_method(m)),
         ast::ii_foreign(i) => ast::ii_foreign(fld.fold_foreign_item(i)),

src/librustpkg/util.rs

@@ -22,6 +22,7 @@ use syntax::{ast, attr, codemap, diagnostic, fold, visit};
 use syntax::attr::AttrMetaMethods;
 use syntax::fold::ast_fold;
 use syntax::visit::Visitor;
+use syntax::util::small_vector::SmallVector;
 use rustc::back::link::output_type_exe;
 use rustc::back::link;
 use rustc::driver::session::{lib_crate, bin_crate};
@@ -99,7 +100,7 @@ fn fold_mod(_ctx: @mut ReadyCtx, m: &ast::_mod, fold: &CrateSetup)
 }
 
 fn fold_item(ctx: @mut ReadyCtx, item: @ast::item, fold: &CrateSetup)
-             -> Option<@ast::item> {
+             -> SmallVector<@ast::item> {
     ctx.path.push(item.ident);
 
     let mut cmds = ~[];
@@ -142,7 +143,7 @@ struct CrateSetup {
 }
 
 impl fold::ast_fold for CrateSetup {
-    fn fold_item(&self, item: @ast::item) -> Option<@ast::item> {
+    fn fold_item(&self, item: @ast::item) -> SmallVector<@ast::item> {
         fold_item(self.ctx, item, self)
     }
     fn fold_mod(&self, module: &ast::_mod) -> ast::_mod {

src/libsyntax/ext/base.rs

@@ -18,6 +18,7 @@ use ext::expand;
 use parse;
 use parse::token;
 use parse::token::{ident_to_str, intern, str_to_ident};
+use util::small_vector::SmallVector;
 
 use std::hashmap::HashMap;
 
@@ -131,7 +132,7 @@ pub type SyntaxExpanderTTItemFunNoCtxt =
 
 pub trait AnyMacro {
     fn make_expr(&self) -> @ast::Expr;
-    fn make_item(&self) -> Option<@ast::item>;
+    fn make_items(&self) -> SmallVector<@ast::item>;
     fn make_stmt(&self) -> @ast::Stmt;
 }