Add a guide to compiler plugins

Fixes #16983.

configure

@@ -926,6 +926,7 @@ do
     make_dir $h/test/doc-guide-pointers
     make_dir $h/test/doc-guide-container
     make_dir $h/test/doc-guide-tasks
+    make_dir $h/test/doc-guide-plugin
     make_dir $h/test/doc-rust
 done
 

mk/docs.mk

@@ -27,7 +27,7 @@
 ######################################################################
 DOCS := index intro tutorial guide guide-ffi guide-macros guide-lifetimes \
 	guide-tasks guide-container guide-pointers guide-testing \
-	guide-runtime complement-bugreport \
+	guide-runtime guide-plugin complement-bugreport \
 	complement-lang-faq complement-design-faq complement-project-faq rust \
     rustdoc guide-unsafe guide-strings reference
 

src/doc/guide-plugin.md

@@ -0,0 +1,259 @@
+% The Rust Compiler Plugins Guide
+
+<div class="unstable-feature">
+
+<p>
+<b>Warning:</b> Plugins are an advanced, unstable feature! For many details,
+the only available documentation is the <a
+href="syntax/index.html"><code>libsyntax</code></a> and <a
+href="rustc/index.html"><code>librustc</code></a> API docs, or even the source
+code itself. These internal compiler APIs are also subject to change at any
+time.
+</p>
+
+<p>
+For defining new syntax it is often much easier to use Rust's <a
+href="guide-macros.html">built-in macro system</a>.
+</p>
+
+<p style="margin-bottom: 0">
+The code in this document uses language features not covered in the Rust
+Guide.  See the <a href="reference.html">Reference Manual</a> for more
+information.
+</p>
+
+</div>
+
+# Introduction
+
+`rustc` can load compiler plugins, which are user-provided libraries that
+extend the compiler's behavior with new syntax extensions, lint checks, etc.
+
+A plugin is a dynamic library crate with a designated "registrar" function that
+registers extensions with `rustc`. Other crates can use these extensions by
+loading the plugin crate with `#[phase(plugin)] extern crate`. See the
+[`rustc::plugin`](rustc/plugin/index.html) documentation for more about the
+mechanics of defining and loading a plugin.
+
+# Syntax extensions
+
+Plugins can extend Rust's syntax in various ways. One kind of syntax extension
+is the procedural macro. These are invoked the same way as [ordinary
+macros](guide-macros.html), but the expansion is performed by arbitrary Rust
+code that manipulates [syntax trees](syntax/ast/index.html) at
+compile time.
+
+Let's write a plugin
+[`roman_numerals.rs`](https://github.com/rust-lang/rust/tree/master/src/test/auxiliary/roman_numerals.rs)
+that implements Roman numeral integer literals.
+
+```ignore
+#![crate_type="dylib"]
+#![feature(plugin_registrar)]
+
+extern crate syntax;
+extern crate rustc;
+
+use syntax::codemap::Span;
+use syntax::parse::token::{IDENT, get_ident};
+use syntax::ast::{TokenTree, TTTok};
+use syntax::ext::base::{ExtCtxt, MacResult, DummyResult, MacExpr};
+use syntax::ext::build::AstBuilder;  // trait for expr_uint
+use rustc::plugin::Registry;
+
+fn expand_rn(cx: &mut ExtCtxt, sp: Span, args: &[TokenTree])
+        -> Box<MacResult + 'static> {
+
+    static NUMERALS: &'static [(&'static str, uint)] = &[
+        ("M", 1000), ("CM", 900), ("D", 500), ("CD", 400),
+        ("C",  100), ("XC",  90), ("L",  50), ("XL",  40),
+        ("X",   10), ("IX",   9), ("V",   5), ("IV",   4),
+        ("I",    1)];
+
+    let text = match args {
+        [TTTok(_, IDENT(s, _))] => get_ident(s).to_string(),
+        _ => {
+            cx.span_err(sp, "argument should be a single identifier");
+            return DummyResult::any(sp);
+        }
+    };
+
+    let mut text = text.as_slice();
+    let mut total = 0u;
+    while !text.is_empty() {
+        match NUMERALS.iter().find(|&&(rn, _)| text.starts_with(rn)) {
+            Some(&(rn, val)) => {
+                total += val;
+                text = text.slice_from(rn.len());
+            }
+            None => {
+                cx.span_err(sp, "invalid Roman numeral");
+                return DummyResult::any(sp);
+            }
+        }
+    }
+
+    MacExpr::new(cx.expr_uint(sp, total))
+}
+
+#[plugin_registrar]
+pub fn plugin_registrar(reg: &mut Registry) {
+    reg.register_macro("rn", expand_rn);
+}
+```
+
+Then we can use `rn!()` like any other macro:
+
+```ignore
+#![feature(phase)]
+
+#[phase(plugin)]
+extern crate roman_numerals;
+
+fn main() {
+    assert_eq!(rn!(MMXV), 2015);
+}
+```
+
+The advantages over a simple `fn(&str) -> uint` are:
+
+* The (arbitrarily complex) conversion is done at compile time.
+* Input validation is also performed at compile time.
+* It can be extended to allow use in patterns, which effectively gives
+  a way to define new literal syntax for any data type.
+
+In addition to procedural macros, you can define new
+[`deriving`](reference.html#deriving)-like attributes and other kinds of
+extensions.  See
+[`Registry::register_syntax_extension`](rustc/plugin/registry/struct.Registry.html#method.register_syntax_extension)
+and the [`SyntaxExtension`
+enum](http://doc.rust-lang.org/syntax/ext/base/enum.SyntaxExtension.html).  For
+a more involved macro example, see
+[`src/libregex_macros/lib.rs`](https://github.com/rust-lang/rust/blob/master/src/libregex_macros/lib.rs)
+in the Rust distribution.
+
+
+## Tips and tricks
+
+To see the results of expanding syntax extensions, run
+`rustc --pretty expanded`. The output represents a whole crate, so you
+can also feed it back in to `rustc`, which will sometimes produce better
+error messages than the original compilation. Note that the
+`--pretty expanded` output may have a different meaning if multiple
+variables of the same name (but different syntax contexts) are in play
+in the same scope. In this case `--pretty expanded,hygiene` will tell
+you about the syntax contexts.
+
+You can use [`syntax::parse`](syntax/parse/index.html) to turn token trees into
+higher-level syntax elements like expressions:
+
+```ignore
+fn expand_foo(cx: &mut ExtCtxt, sp: Span, args: &[TokenTree])
+        -> Box<MacResult+'static> {
+
+    let mut parser =
+        parse::new_parser_from_tts(cx.parse_sess(), cx.cfg(), args.to_slice())
+
+    let expr: P<Expr> = parser.parse_expr();
+```
+
+Looking through [`libsyntax` parser
+code](https://github.com/rust-lang/rust/blob/master/src/libsyntax/parse/parser.rs)
+will give you a feel for how the parsing infrastructure works.
+
+Keep the [`Span`s](syntax/codemap/struct.Span.html) of
+everything you parse, for better error reporting. You can wrap
+[`Spanned`](syntax/codemap/struct.Spanned.html) around
+your custom data structures.
+
+Calling
+[`ExtCtxt::span_fatal`](syntax/ext/base/struct.ExtCtxt.html#method.span_fatal)
+will immediately abort compilation. It's better to instead call
+[`ExtCtxt::span_err`](syntax/ext/base/struct.ExtCtxt.html#method.span_err)
+and return
+[`DummyResult`](syntax/ext/base/struct.DummyResult.html),
+so that the compiler can continue and find further errors.
+
+The example above produced an integer literal using
+[`AstBuilder::expr_uint`](syntax/ext/build/trait.AstBuilder.html#tymethod.expr_uint).
+As an alternative to the `AstBuilder` trait, `libsyntax` provides a set of
+[quasiquote macros](syntax/ext/quote/index.html).  They are undocumented and
+very rough around the edges.  However, the implementation may be a good
+starting point for an improved quasiquote as an ordinary plugin library.
+
+
+# Lint plugins
+
+Plugins can extend [Rust's lint
+infrastructure](reference.html#lint-check-attributes) with additional checks for
+code style, safety, etc. You can see
+[`src/test/auxiliary/lint_plugin_test.rs`](https://github.com/rust-lang/rust/blob/master/src/test/auxiliary/lint_plugin_test.rs)
+for a full example, the core of which is reproduced here:
+
+```ignore
+declare_lint!(TEST_LINT, Warn,
+              "Warn about items named 'lintme'")
+
+struct Pass;
+
+impl LintPass for Pass {
+    fn get_lints(&self) -> LintArray {
+        lint_array!(TEST_LINT)
+    }
+
+    fn check_item(&mut self, cx: &Context, it: &ast::Item) {
+        let name = token::get_ident(it.ident);
+        if name.get() == "lintme" {
+            cx.span_lint(TEST_LINT, it.span, "item is named 'lintme'");
+        }
+    }
+}
+
+#[plugin_registrar]
+pub fn plugin_registrar(reg: &mut Registry) {
+    reg.register_lint_pass(box Pass as LintPassObject);
+}
+```
+
+Then code like
+
+```ignore
+#[phase(plugin)]
+extern crate lint_plugin_test;
+
+fn lintme() { }
+```
+
+will produce a compiler warning:
+
+```txt
+foo.rs:4:1: 4:16 warning: item is named 'lintme', #[warn(test_lint)] on by default
+foo.rs:4 fn lintme() { }
+         ^~~~~~~~~~~~~~~
+```
+
+The components of a lint plugin are:
+
+* one or more `declare_lint!` invocations, which define static
+  [`Lint`](rustc/lint/struct.Lint.html) structs;
+
+* a struct holding any state needed by the lint pass (here, none);
+
+* a [`LintPass`](rustc/lint/trait.LintPass.html)
+  implementation defining how to check each syntax element. A single
+  `LintPass` may call `span_lint` for several different `Lint`s, but should
+  register them all through the `get_lints` method.
+
+Lint passes are syntax traversals, but they run at a late stage of compilation
+where type information is available. `rustc`'s [built-in
+lints](https://github.com/rust-lang/rust/blob/master/src/librustc/lint/builtin.rs)
+mostly use the same infrastructure as lint plugins, and provide examples of how
+to access type information.
+
+Lints defined by plugins are controlled by the usual [attributes and compiler
+flags](reference.html#lint-check-attributes), e.g. `#[allow(test_lint)]` or
+`-A test-lint`. These identifiers are derived from the first argument to
+`declare_lint!`, with appropriate case and punctuation conversion.
+
+You can run `rustc -W help foo.rs` to see a list of lints known to `rustc`,
+including those provided by plugins loaded by `foo.rs`.

src/doc/index.md

@@ -63,6 +63,7 @@ a guide that can help you out:
 * [Macros](guide-macros.html)
 * [Testing](guide-testing.html)
 * [Rust's Runtime](guide-runtime.html)
+* [Compiler Plugins](guide-plugin.html)
 
 # Tools
 

src/doc/po4a.conf

@@ -13,6 +13,7 @@
 [type: text] src/doc/guide-ffi.md $lang:doc/l10n/$lang/guide-ffi.md
 [type: text] src/doc/guide-lifetimes.md $lang:doc/l10n/$lang/guide-lifetimes.md
 [type: text] src/doc/guide-macros.md $lang:doc/l10n/$lang/guide-macros.md
+[type: text] src/doc/guide-plugin.md $lang:doc/l10n/$lang/guide-plugin.md
 [type: text] src/doc/guide-pointers.md $lang:doc/l10n/$lang/guide-pointers.md
 [type: text] src/doc/guide-runtime.md $lang:doc/l10n/$lang/guide-runtime.md
 [type: text] src/doc/guide-strings.md $lang:doc/l10n/$lang/guide-strings.md

src/librustc/plugin/mod.rs

@@ -53,8 +53,8 @@
  * If you also need the plugin crate available at runtime, use
  * `phase(plugin, link)`.
  *
- * See `src/test/auxiliary/macro_crate_test.rs` and `src/libfourcc`
- * for examples of syntax extension plugins.
+ * See [the compiler plugin guide](../../guide-plugin.html)
+ * for more examples.
  */
 
 pub use self::registry::Registry;

src/test/auxiliary/roman_numerals.rs

@@ -0,0 +1,70 @@
+// Copyright 2014 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.
+
+// force-host
+
+#![crate_type="dylib"]
+#![feature(plugin_registrar)]
+
+extern crate syntax;
+extern crate rustc;
+
+use syntax::codemap::Span;
+use syntax::parse::token::{IDENT, get_ident};
+use syntax::ast::{TokenTree, TTTok};
+use syntax::ext::base::{ExtCtxt, MacResult, DummyResult, MacExpr};
+use syntax::ext::build::AstBuilder;  // trait for expr_uint
+use rustc::plugin::Registry;
+
+// WARNING WARNING WARNING WARNING WARNING
+// =======================================
+//
+// This code also appears in src/doc/guide-plugin.md. Please keep
+// the two copies in sync!  FIXME: have rustdoc read this file
+
+fn expand_rn(cx: &mut ExtCtxt, sp: Span, args: &[TokenTree])
+        -> Box<MacResult + 'static> {
+
+    static NUMERALS: &'static [(&'static str, uint)] = &[
+        ("M", 1000), ("CM", 900), ("D", 500), ("CD", 400),
+        ("C",  100), ("XC",  90), ("L",  50), ("XL",  40),
+        ("X",   10), ("IX",   9), ("V",   5), ("IV",   4),
+        ("I",    1)];
+
+    let text = match args {
+        [TTTok(_, IDENT(s, _))] => get_ident(s).to_string(),
+        _ => {
+            cx.span_err(sp, "argument should be a single identifier");
+            return DummyResult::any(sp);
+        }
+    };
+
+    let mut text = text.as_slice();
+    let mut total = 0u;
+    while !text.is_empty() {
+        match NUMERALS.iter().find(|&&(rn, _)| text.starts_with(rn)) {
+            Some(&(rn, val)) => {
+                total += val;
+                text = text.slice_from(rn.len());
+            }
+            None => {
+                cx.span_err(sp, "invalid Roman numeral");
+                return DummyResult::any(sp);
+            }
+        }
+    }
+
+    MacExpr::new(cx.expr_uint(sp, total))
+}
+
+#[plugin_registrar]
+pub fn plugin_registrar(reg: &mut Registry) {
+    reg.register_macro("rn", expand_rn);
+}