Add initial support for a new formatting syntax

The new macro is available under the name ifmt! (only an intermediate name)

3 files changed, 725 insertions, 1 deletions

diff --git a/src/libsyntax/ext/base.rs b/src/libsyntax/ext/base.rs
index 6ed5ca3e402..99f74543e79 100644
--- a/src/libsyntax/ext/base.rs
+++ b/src/libsyntax/ext/base.rs
@@ -139,6 +139,8 @@ pub fn syntax_expander_table() -> SyntaxEnv {
                                 ext::tt::macro_rules::add_new_extension));
     syntax_expanders.insert(intern(&"fmt"),
                             builtin_normal_tt(ext::fmt::expand_syntax_ext));
+    syntax_expanders.insert(intern(&"ifmt"),
+                            builtin_normal_tt(ext::ifmt::expand_syntax_ext));
     syntax_expanders.insert(
         intern(&"auto_encode"),
         @SE(ItemDecorator(ext::auto_encode::expand_auto_encode)));
diff --git a/src/libsyntax/ext/expand.rs b/src/libsyntax/ext/expand.rs
index c7020b990bf..a928680e093 100644
--- a/src/libsyntax/ext/expand.rs
+++ b/src/libsyntax/ext/expand.rs
@@ -1014,7 +1014,9 @@ pub fn expand_crate(parse_sess: @mut parse::ParseSess,
         .. *afp};
     let f = make_fold(f_pre);
 
-    @f.fold_crate(c)
+    let ret = @f.fold_crate(c);
+    parse_sess.span_diagnostic.handler().abort_if_errors();
+    return ret;
 }
 
 // given a function from idents to idents, produce
diff --git a/src/libsyntax/ext/ifmt.rs b/src/libsyntax/ext/ifmt.rs
new file mode 100644
index 00000000000..5cf5fdba632
--- /dev/null
+++ b/src/libsyntax/ext/ifmt.rs
@@ -0,0 +1,720 @@
+// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use ast;
+use codemap::{span, respan};
+use ext::base::*;
+use ext::base;
+use ext::build::AstBuilder;
+use rsparse = parse;
+use parse::token;
+
+use std::fmt::parse;
+use std::hashmap::{HashMap, HashSet};
+use std::vec;
+
+#[deriving(Eq)]
+enum ArgumentType {
+    Unknown,
+    Known(@str),
+    Unsigned,
+    String,
+}
+
+struct Context {
+    ecx: @ExtCtxt,
+    fmtsp: span,
+
+    // Parsed argument expressions and the types that we've found so far for
+    // them.
+    args: ~[@ast::expr],
+    arg_types: ~[Option<ArgumentType>],
+    // Parsed named expressions and the types that we've found for them so far
+    names: HashMap<@str, @ast::expr>,
+    name_types: HashMap<@str, ArgumentType>,
+
+    // Collection of the compiled `rt::Piece` structures
+    pieces: ~[@ast::expr],
+    name_positions: HashMap<@str, uint>,
+    method_statics: ~[@ast::item],
+
+    // Updated as arguments are consumed or methods are entered
+    nest_level: uint,
+    next_arg: uint,
+}
+
+impl Context {
+    /// Parses the arguments from the given list of tokens, returning None if
+    /// there's a parse error so we can continue parsing other fmt! expressions.
+    fn parse_args(&mut self, sp: span,
+                  tts: &[ast::token_tree]) -> Option<@ast::expr> {
+        let p = rsparse::new_parser_from_tts(self.ecx.parse_sess(),
+                                             self.ecx.cfg(),
+                                             tts.to_owned());
+        if *p.token == token::EOF {
+            self.ecx.span_err(sp, "ifmt! expects at least one argument");
+            return None;
+        }
+        let fmtstr = p.parse_expr();
+        let mut named = false;
+        while *p.token != token::EOF {
+            if !p.eat(&token::COMMA) {
+                self.ecx.span_err(sp, "expected token: `,`");
+                return None;
+            }
+            if named || (token::is_ident(p.token) &&
+                         p.look_ahead(1, |t| *t == token::EQ)) {
+                named = true;
+                let ident = match *p.token {
+                    token::IDENT(i, _) => {
+                        p.bump();
+                        i
+                    }
+                    _ if named => {
+                        self.ecx.span_err(*p.span,
+                                          "expected ident, positional arguments \
+                                           cannot follow named arguments");
+                        return None;
+                    }
+                    _ => {
+                        self.ecx.span_err(*p.span,
+                                          fmt!("expected ident for named \
+                                                argument, but found `%s`",
+                                               p.this_token_to_str()));
+                        return None;
+                    }
+                };
+                let name = self.ecx.str_of(ident);
+                p.expect(&token::EQ);
+                let e = p.parse_expr();
+                match self.names.find(&name) {
+                    None => {}
+                    Some(prev) => {
+                        self.ecx.span_err(e.span, fmt!("duplicate argument \
+                                                        named `%s`", name));
+                        self.ecx.parse_sess.span_diagnostic.span_note(
+                            prev.span, "previously here");
+                        loop
+                    }
+                }
+                self.names.insert(name, e);
+            } else {
+                self.args.push(p.parse_expr());
+                self.arg_types.push(None);
+            }
+        }
+        return Some(fmtstr);
+    }
+
+    /// Verifies one piece of a parse string. All errors are not emitted as
+    /// fatal so we can continue giving errors about this and possibly other
+    /// format strings.
+    fn verify_piece(&mut self, p: &parse::Piece) {
+        match *p {
+            parse::String(*) => {}
+            parse::CurrentArgument => {
+                if self.nest_level == 0 {
+                    self.ecx.span_err(self.fmtsp,
+                                      "`#` reference used with nothing to \
+                                       reference back to");
+                }
+            }
+            parse::Argument(ref arg) => {
+                // argument first (it's first in the format string)
+                let pos = match arg.position {
+                    parse::ArgumentNext => {
+                        let i = self.next_arg;
+                        if self.check_positional_ok() {
+                            self.next_arg += 1;
+                        }
+                        Left(i)
+                    }
+                    parse::ArgumentIs(i) => Left(i),
+                    parse::ArgumentNamed(s) => Right(s.to_managed()),
+                };
+                let ty = if arg.format.ty == "" {
+                    Unknown
+                } else { Known(arg.format.ty.to_managed()) };
+                self.verify_arg_type(pos, ty);
+
+                // width/precision next
+                self.verify_count(arg.format.width);
+                self.verify_count(arg.format.precision);
+
+                // and finally the method being applied
+                match arg.method {
+                    None => {}
+                    Some(ref method) => { self.verify_method(pos, *method); }
+                }
+            }
+        }
+    }
+
+    fn verify_pieces(&mut self, pieces: &[parse::Piece]) {
+        for piece in pieces.iter() {
+            self.verify_piece(piece);
+        }
+    }
+
+    fn verify_count(&mut self, c: parse::Count) {
+        match c {
+            parse::CountImplied | parse::CountIs(*) => {}
+            parse::CountIsParam(i) => {
+                self.verify_arg_type(Left(i), Unsigned);
+            }
+            parse::CountIsNextParam => {
+                if self.check_positional_ok() {
+                    self.verify_arg_type(Left(self.next_arg), Unsigned);
+                    self.next_arg += 1;
+                }
+            }
+        }
+    }
+
+    fn check_positional_ok(&mut self) -> bool {
+        if self.nest_level != 0 {
+            self.ecx.span_err(self.fmtsp, "cannot use implicit positional \
+                                           arguments nested inside methods");
+            false
+        } else {
+            true
+        }
+    }
+
+    fn verify_method(&mut self, pos: Either<uint, @str>, m: &parse::Method) {
+        self.nest_level += 1;
+        match *m {
+            parse::Plural(_, ref arms, ref default) => {
+                let mut seen_cases = HashSet::new();
+                self.verify_arg_type(pos, Unsigned);
+                for arm in arms.iter() {
+                    if !seen_cases.insert(arm.selector) {
+                        match arm.selector {
+                            Left(name) => {
+                                self.ecx.span_err(self.fmtsp,
+                                                  fmt!("duplicate selector \
+                                                       `%?`", name));
+                            }
+                            Right(idx) => {
+                                self.ecx.span_err(self.fmtsp,
+                                                  fmt!("duplicate selector \
+                                                       `=%u`", idx));
+                            }
+                        }
+                    }
+                    self.verify_pieces(arm.result);
+                }
+                self.verify_pieces(*default);
+            }
+            parse::Select(ref arms, ref default) => {
+                self.verify_arg_type(pos, String);
+                let mut seen_cases = HashSet::new();
+                for arm in arms.iter() {
+                    if !seen_cases.insert(arm.selector) {
+                        self.ecx.span_err(self.fmtsp,
+                                          fmt!("duplicate selector `%s`",
+                                               arm.selector));
+                    } else if arm.selector == "" {
+                        self.ecx.span_err(self.fmtsp,
+                                          "empty selector in `select`");
+                    }
+                    self.verify_pieces(arm.result);
+                }
+                self.verify_pieces(*default);
+            }
+        }
+        self.nest_level -= 1;
+    }
+
+    fn verify_arg_type(&mut self, arg: Either<uint, @str>, ty: ArgumentType) {
+        match arg {
+            Left(arg) => {
+                if arg < 0 || self.args.len() <= arg {
+                    let msg = fmt!("invalid reference to argument `%u` (there \
+                                    are %u arguments)", arg, self.args.len());
+                    self.ecx.span_err(self.fmtsp, msg);
+                    return;
+                }
+                self.verify_same(self.args[arg].span, ty, self.arg_types[arg]);
+                if ty != Unknown || self.arg_types[arg].is_none() {
+                    self.arg_types[arg] = Some(ty);
+                }
+            }
+
+            Right(name) => {
+                let span = match self.names.find(&name) {
+                    Some(e) => e.span,
+                    None => {
+                        let msg = fmt!("There is no argument named `%s`", name);
+                        self.ecx.span_err(self.fmtsp, msg);
+                        return;
+                    }
+                };
+                self.verify_same(span, ty,
+                                 self.name_types.find(&name).map(|&x| *x));
+                if ty != Unknown || !self.name_types.contains_key(&name) {
+                    self.name_types.insert(name, ty);
+                }
+                // Assign this named argument a slot in the arguments array if
+                // it hasn't already been assigned a slot.
+                if !self.name_positions.contains_key(&name) {
+                    let slot = self.name_positions.len();
+                    self.name_positions.insert(name, slot);
+                }
+            }
+        }
+    }
+
+    /// When we're keeping track of the types that are declared for certain
+    /// arguments, we assume that `None` means we haven't seen this argument
+    /// yet, `Some(None)` means that we've seen the argument, but no format was
+    /// specified, and `Some(Some(x))` means that the argument was declared to
+    /// have type `x`.
+    ///
+    /// Obviously `Some(Some(x)) != Some(Some(y))`, but we consider it true
+    /// that: `Some(None) == Some(Some(x))`
+    fn verify_same(&self, sp: span, ty: ArgumentType,
+                   before: Option<ArgumentType>) {
+        if ty == Unknown { return }
+        let cur = match before {
+            Some(Unknown) | None => return,
+            Some(t) => t,
+        };
+        if ty == cur { return }
+        match (cur, ty) {
+            (Known(cur), Known(ty)) => {
+                self.ecx.span_err(sp,
+                                  fmt!("argument redeclared with type `%s` when \
+                                        it was previously `%s`", ty, cur));
+            }
+            (Known(cur), _) => {
+                self.ecx.span_err(sp,
+                                  fmt!("argument used to format with `%s` was \
+                                        attempted to not be used for formatting",
+                                        cur));
+            }
+            (_, Known(ty)) => {
+                self.ecx.span_err(sp,
+                                  fmt!("argument previously used as a format \
+                                        argument attempted to be used as `%s`",
+                                        ty));
+            }
+            (_, _) => {
+                self.ecx.span_err(sp, "argument declared with multiple formats");
+            }
+        }
+    }
+
+    /// Translate a `parse::Piece` to a static `rt::Piece`
+    fn trans_piece(&mut self, piece: &parse::Piece) -> @ast::expr {
+        let sp = self.fmtsp;
+        let rtpath = |s: &str| {
+            ~[self.ecx.ident_of("std"), self.ecx.ident_of("fmt"),
+              self.ecx.ident_of("rt"), self.ecx.ident_of(s)]
+        };
+        let ctpath = |s: &str| {
+            ~[self.ecx.ident_of("std"), self.ecx.ident_of("fmt"),
+              self.ecx.ident_of("parse"), self.ecx.ident_of(s)]
+        };
+        let none = || {
+            let p = self.ecx.path(sp, ~[self.ecx.ident_of("None")]);
+            self.ecx.expr_path(p)
+        };
+        let some = |e: @ast::expr| {
+            self.ecx.expr_call_ident(sp, self.ecx.ident_of("Some"), ~[e])
+        };
+        let trans_count = |c: parse::Count| {
+            match c {
+                parse::CountIs(i) => {
+                    self.ecx.expr_call_global(sp, ctpath("CountIs"),
+                                              ~[self.ecx.expr_uint(sp, i)])
+                }
+                parse::CountIsParam(i) => {
+                    self.ecx.expr_call_global(sp, ctpath("CountIsParam"),
+                                              ~[self.ecx.expr_uint(sp, i)])
+                }
+                parse::CountImplied => {
+                    let path = self.ecx.path_global(sp, ctpath("CountImplied"));
+                    self.ecx.expr_path(path)
+                }
+                parse::CountIsNextParam => {
+                    let path = self.ecx.path_global(sp, ctpath("CountIsNextParam"));
+                    self.ecx.expr_path(path)
+                }
+            }
+        };
+        let trans_method = |method: &parse::Method| {
+            let method = match *method {
+                parse::Select(ref arms, ref default) => {
+                    let arms = arms.iter().transform(|arm| {
+                        let p = self.ecx.path_global(sp, rtpath("SelectArm"));
+                        let result = arm.result.iter().transform(|p| {
+                            self.trans_piece(p)
+                        }).collect();
+                        let s = arm.selector.to_managed();
+                        let selector = self.ecx.expr_str(sp, s);
+                        self.ecx.expr_struct(sp, p, ~[
+                            self.ecx.field_imm(sp,
+                                               self.ecx.ident_of("selector"),
+                                               selector),
+                            self.ecx.field_imm(sp, self.ecx.ident_of("result"),
+                                               self.ecx.expr_vec_slice(sp, result)),
+                        ])
+                    }).collect();
+                    let default = default.iter().transform(|p| {
+                        self.trans_piece(p)
+                    }).collect();
+                    self.ecx.expr_call_global(sp, rtpath("Select"), ~[
+                        self.ecx.expr_vec_slice(sp, arms),
+                        self.ecx.expr_vec_slice(sp, default),
+                    ])
+                }
+                parse::Plural(offset, ref arms, ref default) => {
+                    let offset = match offset {
+                        Some(i) => { some(self.ecx.expr_uint(sp, i)) }
+                        None => { none() }
+                    };
+                    let arms = arms.iter().transform(|arm| {
+                        let p = self.ecx.path_global(sp, rtpath("PluralArm"));
+                        let result = arm.result.iter().transform(|p| {
+                            self.trans_piece(p)
+                        }).collect();
+                        let (lr, selarg) = match arm.selector {
+                            Left(t) => {
+                                let p = ctpath(fmt!("%?", t));
+                                let p = self.ecx.path_global(sp, p);
+                                (self.ecx.ident_of("Left"),
+                                 self.ecx.expr_path(p))
+                            }
+                            Right(i) => {
+                                (self.ecx.ident_of("Right"),
+                                 self.ecx.expr_uint(sp, i))
+                            }
+                        };
+                        let selector = self.ecx.expr_call_ident(sp,
+                                lr, ~[selarg]);
+                        self.ecx.expr_struct(sp, p, ~[
+                            self.ecx.field_imm(sp,
+                                               self.ecx.ident_of("selector"),
+                                               selector),
+                            self.ecx.field_imm(sp, self.ecx.ident_of("result"),
+                                               self.ecx.expr_vec_slice(sp, result)),
+                        ])
+                    }).collect();
+                    let default = default.iter().transform(|p| {
+                        self.trans_piece(p)
+                    }).collect();
+                    self.ecx.expr_call_global(sp, rtpath("Plural"), ~[
+                        offset,
+                        self.ecx.expr_vec_slice(sp, arms),
+                        self.ecx.expr_vec_slice(sp, default),
+                    ])
+                }
+            };
+            let life = self.ecx.lifetime(sp, self.ecx.ident_of("static"));
+            let ty = self.ecx.ty_path(self.ecx.path_all(
+                sp,
+                true,
+                rtpath("Method"),
+                Some(life),
+                ~[]
+            ), None);
+            let st = ast::item_static(ty, ast::m_imm, method);
+            let static_name = self.ecx.ident_of(fmt!("__static_method_%u",
+                                                     self.method_statics.len()));
+            let item = self.ecx.item(sp, static_name, ~[], st);
+            self.method_statics.push(item);
+            self.ecx.expr_ident(sp, static_name)
+        };
+
+        match *piece {
+            parse::String(s) => {
+                self.ecx.expr_call_global(sp, rtpath("String"),
+                                          ~[self.ecx.expr_str(sp, s.to_managed())])
+            }
+            parse::CurrentArgument => {
+                let nil = self.ecx.expr_lit(sp, ast::lit_nil);
+                self.ecx.expr_call_global(sp, rtpath("CurrentArgument"), ~[nil])
+            }
+            parse::Argument(ref arg) => {
+                // Translate the position
+                let pos = match arg.position {
+                    // These two have a direct mapping
+                    parse::ArgumentNext => {
+                        let path = self.ecx.path_global(sp,
+                                                        rtpath("ArgumentNext"));
+                        self.ecx.expr_path(path)
+                    }
+                    parse::ArgumentIs(i) => {
+                        self.ecx.expr_call_global(sp, rtpath("ArgumentIs"),
+                                                  ~[self.ecx.expr_uint(sp, i)])
+                    }
+                    // Named arguments are converted to positional arguments at
+                    // the end of the list of arguments
+                    parse::ArgumentNamed(n) => {
+                        let n = n.to_managed();
+                        let i = match self.name_positions.find_copy(&n) {
+                            Some(i) => i,
+                            None => 0, // error already emitted elsewhere
+                        };
+                        let i = i + self.args.len();
+                        self.ecx.expr_call_global(sp, rtpath("ArgumentIs"),
+                                                  ~[self.ecx.expr_uint(sp, i)])
+                    }
+                };
+
+                // Translate the format
+                let fill = match arg.format.fill { Some(c) => c, None => ' ' };
+                let fill = self.ecx.expr_lit(sp, ast::lit_int(fill as i64,
+                                                              ast::ty_char));
+                let align = match arg.format.align {
+                    None | Some(parse::AlignLeft) => {
+                        self.ecx.expr_bool(sp, true)
+                    }
+                    Some(parse::AlignRight) => {
+                        self.ecx.expr_bool(sp, false)
+                    }
+                };
+                let flags = self.ecx.expr_uint(sp, arg.format.flags);
+                let prec = trans_count(arg.format.precision);
+                let width = trans_count(arg.format.width);
+                let path = self.ecx.path_global(sp, rtpath("FormatSpec"));
+                let fmt = self.ecx.expr_struct(sp, path, ~[
+                    self.ecx.field_imm(sp, self.ecx.ident_of("fill"), fill),
+                    self.ecx.field_imm(sp, self.ecx.ident_of("alignleft"), align),
+                    self.ecx.field_imm(sp, self.ecx.ident_of("flags"), flags),
+                    self.ecx.field_imm(sp, self.ecx.ident_of("precision"), prec),
+                    self.ecx.field_imm(sp, self.ecx.ident_of("width"), width),
+                ]);
+
+                // Translate the method (if any)
+                let method = match arg.method {
+                    None => { none() }
+                    Some(ref m) => {
+                        let m = trans_method(*m);
+                        some(self.ecx.expr_addr_of(sp, m))
+                    }
+                };
+                let path = self.ecx.path_global(sp, rtpath("Argument"));
+                let s = self.ecx.expr_struct(sp, path, ~[
+                    self.ecx.field_imm(sp, self.ecx.ident_of("position"), pos),
+                    self.ecx.field_imm(sp, self.ecx.ident_of("format"), fmt),
+                    self.ecx.field_imm(sp, self.ecx.ident_of("method"), method),
+                ]);
+                self.ecx.expr_call_global(sp, rtpath("Argument"), ~[s])
+            }
+        }
+    }
+
+    /// Actually builds the expression which the ifmt! block will be expanded
+    /// to
+    fn to_expr(&self) -> @ast::expr {
+        let mut lets = ~[];
+        let mut locals = ~[];
+        let mut names = vec::from_fn(self.name_positions.len(), |_| None);
+
+        // First, declare all of our methods that are statics
+        for &method in self.method_statics.iter() {
+            let decl = respan(self.fmtsp, ast::decl_item(method));
+            lets.push(@respan(self.fmtsp,
+                              ast::stmt_decl(@decl, self.ecx.next_id())));
+        }
+
+        // Next, build up the static array which will become our precompiled
+        // format "string"
+        let fmt = self.ecx.expr_vec(self.fmtsp, self.pieces.clone());
+        let ty = ast::ty_fixed_length_vec(
+            self.ecx.ty_mt(
+                self.ecx.ty_path(self.ecx.path_all(
+                    self.fmtsp,
+                    true, ~[
+                        self.ecx.ident_of("std"),
+                        self.ecx.ident_of("fmt"),
+                        self.ecx.ident_of("rt"),
+                        self.ecx.ident_of("Piece"),
+                    ],
+                    Some(self.ecx.lifetime(self.fmtsp, self.ecx.ident_of("static"))),
+                    ~[]
+                ), None),
+                ast::m_imm
+            ),
+            self.ecx.expr_uint(self.fmtsp, self.pieces.len())
+        );
+        let ty = self.ecx.ty(self.fmtsp, ty);
+        let st = ast::item_static(ty, ast::m_imm, fmt);
+        let static_name = self.ecx.ident_of("__static_fmtstr");
+        let item = self.ecx.item(self.fmtsp, static_name, ~[], st);
+        let decl = respan(self.fmtsp, ast::decl_item(item));
+        lets.push(@respan(self.fmtsp, ast::stmt_decl(@decl, self.ecx.next_id())));
+
+        // Right now there is a bug such that for the expression:
+        //      foo(bar(&1))
+        // the lifetime of `1` doesn't outlast the call to `bar`, so it's not
+        // vald for the call to `foo`. To work around this all arguments to the
+        // fmt! string are shoved into locals.
+        for (i, &e) in self.args.iter().enumerate() {
+            if self.arg_types[i].is_none() { loop } // error already generated
+
+            let name = self.ecx.ident_of(fmt!("__arg%u", i));
+            lets.push(self.ecx.stmt_let(e.span, false, name, e));
+            locals.push(self.format_arg(e.span, Left(i), name));
+        }
+        for (&name, &e) in self.names.iter() {
+            if !self.name_types.contains_key(&name) { loop }
+
+            let lname = self.ecx.ident_of(fmt!("__arg%s", name));
+            lets.push(self.ecx.stmt_let(e.span, false, lname, e));
+            names[*self.name_positions.get(&name)] =
+                Some(self.format_arg(e.span, Right(name), lname));
+        }
+
+        let args = names.consume_iter().transform(|a| a.unwrap());
+        let mut args = locals.consume_iter().chain_(args);
+
+        // Next, build up the actual call to the sprintf function.
+        let result = self.ecx.expr_call_global(self.fmtsp, ~[
+                self.ecx.ident_of("std"),
+                self.ecx.ident_of("fmt"),
+                self.ecx.ident_of("sprintf"),
+            ], ~[
+                self.ecx.expr_ident(self.fmtsp, static_name),
+                self.ecx.expr_vec(self.fmtsp, args.collect()),
+            ]);
+
+        // sprintf is unsafe, but we just went through a lot of work to
+        // validate that our call is save, so inject the unsafe block for the
+        // user.
+        let result = self.ecx.expr_block(ast::Block {
+           view_items: ~[],
+           stmts: ~[],
+           expr: Some(result),
+           id: self.ecx.next_id(),
+           rules: ast::UnsafeBlock,
+           span: self.fmtsp,
+        });
+
+        self.ecx.expr_block(self.ecx.block(self.fmtsp, lets, Some(result)))
+    }
+
+    fn format_arg(&self, sp: span, arg: Either<uint, @str>,
+                  ident: ast::ident) -> @ast::expr {
+        let mut ty = match arg {
+            Left(i) => self.arg_types[i].unwrap(),
+            Right(s) => *self.name_types.get(&s)
+        };
+        // Default types to '?' if nothing else is specified.
+        if ty == Unknown {
+            ty = Known(@"?");
+        }
+        let argptr = self.ecx.expr_addr_of(sp, self.ecx.expr_ident(sp, ident));
+        match ty {
+            Known(tyname) => {
+                let fmt_trait = match tyname.as_slice() {
+                    "?" => "Poly",
+                    "d" | "i" => "Signed",
+                    "u" => "Unsigned",
+                    "b" => "Bool",
+                    "c" => "Char",
+                    "o" => "Octal",
+                    "x" => "LowerHex",
+                    "X" => "UpperHex",
+                    "s" => "String",
+                    "p" => "Pointer",
+                    _ => {
+                        self.ecx.span_err(sp, fmt!("unknown format trait \
+                                                    `%s`", tyname));
+                        "Dummy"
+                    }
+                };
+                let format_fn = self.ecx.path_global(sp, ~[
+                        self.ecx.ident_of("std"),
+                        self.ecx.ident_of("fmt"),
+                        self.ecx.ident_of(fmt_trait),
+                        self.ecx.ident_of("fmt"),
+                    ]);
+                self.ecx.expr_call_global(sp, ~[
+                        self.ecx.ident_of("std"),
+                        self.ecx.ident_of("fmt"),
+                        self.ecx.ident_of("argument"),
+                    ], ~[self.ecx.expr_path(format_fn), argptr])
+            }
+            String => {
+                self.ecx.expr_call_global(sp, ~[
+                        self.ecx.ident_of("std"),
+                        self.ecx.ident_of("fmt"),
+                        self.ecx.ident_of("argumentstr"),
+                    ], ~[argptr])
+            }
+            Unsigned => {
+                self.ecx.expr_call_global(sp, ~[
+                        self.ecx.ident_of("std"),
+                        self.ecx.ident_of("fmt"),
+                        self.ecx.ident_of("argumentuint"),
+                    ], ~[argptr])
+            }
+            Unknown => { fail!() }
+        }
+    }
+}
+
+pub fn expand_syntax_ext(ecx: @ExtCtxt, sp: span,
+                         tts: &[ast::token_tree]) -> base::MacResult {
+    let mut cx = Context {
+        ecx: ecx,
+        args: ~[],
+        arg_types: ~[],
+        names: HashMap::new(),
+        name_positions: HashMap::new(),
+        name_types: HashMap::new(),
+        nest_level: 0,
+        next_arg: 0,
+        pieces: ~[],
+        method_statics: ~[],
+        fmtsp: sp,
+    };
+    let efmt = match cx.parse_args(sp, tts) {
+        Some(e) => e,
+        None => { return MRExpr(ecx.expr_uint(sp, 2)); }
+    };
+    cx.fmtsp = efmt.span;
+    let fmt = expr_to_str(ecx, efmt,
+                          ~"first argument to ifmt! must be a string literal.");
+
+    let mut err = false;
+    do parse::parse_error::cond.trap(|m| {
+        if !err {
+            err = true;
+            ecx.span_err(efmt.span, m);
+        }
+    }).inside {
+        for piece in parse::Parser::new(fmt) {
+            if !err {
+                cx.verify_piece(&piece);
+                let piece = cx.trans_piece(&piece);
+                cx.pieces.push(piece);
+            }
+        }
+    }
+    if err { return MRExpr(efmt) }
+
+    // Make sure that all arguments were used and all arguments have types.
+    for (i, ty) in cx.arg_types.iter().enumerate() {
+        if ty.is_none() {
+            ecx.span_err(cx.args[i].span, "argument never used");
+        }
+    }
+    for (name, e) in cx.names.iter() {
+        if !cx.name_types.contains_key(name) {
+            ecx.span_err(e.span, "named argument never used");
+        }
+    }
+
+    MRExpr(cx.to_expr())
+}