rustdoc: Fix documenting rustc-macro crates

This commit adds a "hack" to the session to track whether we're a rustdoc
session or not. If we're rustdoc then we skip the expansion to add the
rustc-macro infrastructure.

Closes rust-lang#36820

Author: alexcrichton

src/bootstrap/step.rs

@@ -486,7 +486,6 @@ impl<'a> Step<'a> {
             Source::CheckCodegenUnits { compiler } |
             Source::CheckIncremental { compiler } |
             Source::CheckUi { compiler } |
-            Source::CheckRustdoc { compiler } |
             Source::CheckPretty { compiler } |
             Source::CheckCFail { compiler } |
             Source::CheckRPassValgrind { compiler } |
@@ -509,6 +508,7 @@ impl<'a> Step<'a> {
                     self.debugger_scripts(compiler.stage),
                 ]
             }
+            Source::CheckRustdoc { compiler } |
             Source::CheckRPassFull { compiler } |
             Source::CheckRFailFull { compiler } |
             Source::CheckCFailFull { compiler } |

src/librustc/session/config.rs

@@ -287,6 +287,11 @@ top_level_options!(
         alt_std_name: Option<String> [TRACKED],
         // Indicates how the compiler should treat unstable features
         unstable_features: UnstableFeatures [TRACKED],
+
+        // Indicates whether this run of the compiler is actually rustdoc. This
+        // is currently just a hack and will be removed eventually, so please
+        // try to not rely on this too much.
+        actually_rustdoc: bool [TRACKED],
     }
 );
 
@@ -439,6 +444,7 @@ pub fn basic_options() -> Options {
         libs: Vec::new(),
         unstable_features: UnstableFeatures::Disallow,
         debug_assertions: true,
+        actually_rustdoc: false,
     }
 }
 
@@ -1536,6 +1542,7 @@ pub fn build_session_options_and_crate_config(matches: &getopts::Matches)
         libs: libs,
         unstable_features: UnstableFeatures::from_environment(),
         debug_assertions: debug_assertions,
+        actually_rustdoc: false,
     },
     cfg)
 }

src/librustc_driver/driver.rs

@@ -703,18 +703,23 @@ pub fn phase_2_configure_and_expand<'a, F>(sess: &Session,
                                          sess.diagnostic())
     });
 
-    krate = time(time_passes, "maybe creating a macro crate", || {
-        let crate_types = sess.crate_types.borrow();
-        let is_rustc_macro_crate = crate_types.contains(&config::CrateTypeRustcMacro);
-        let num_crate_types = crate_types.len();
-        syntax_ext::rustc_macro_registrar::modify(&sess.parse_sess,
-                                                  &mut resolver,
-                                                  krate,
-                                                  is_rustc_macro_crate,
-                                                  num_crate_types,
-                                                  sess.diagnostic(),
-                                                  &sess.features.borrow())
-    });
+    // If we're in rustdoc we're always compiling as an rlib, but that'll trip a
+    // bunch of checks in the `modify` function below. For now just skip this
+    // step entirely if we're rustdoc as it's not too useful anyway.
+    if !sess.opts.actually_rustdoc {
+        krate = time(time_passes, "maybe creating a macro crate", || {
+            let crate_types = sess.crate_types.borrow();
+            let num_crate_types = crate_types.len();
+            let is_rustc_macro_crate = crate_types.contains(&config::CrateTypeRustcMacro);
+            syntax_ext::rustc_macro_registrar::modify(&sess.parse_sess,
+                                                      &mut resolver,
+                                                      krate,
+                                                      is_rustc_macro_crate,
+                                                      num_crate_types,
+                                                      sess.diagnostic(),
+                                                      &sess.features.borrow())
+        });
+    }
 
     if sess.opts.debugging_opts.input_stats {
         println!("Post-expansion node count: {}", count_nodes(&krate));

src/librustdoc/core.rs

@@ -150,6 +150,7 @@ pub fn run_core(search_paths: SearchPaths,
         target_triple: triple.unwrap_or(config::host_triple().to_string()),
         // Ensure that rustdoc works even if rustc is feature-staged
         unstable_features: UnstableFeatures::Allow,
+        actually_rustdoc: true,
         ..config::basic_options().clone()
     };
 

src/test/rustdoc/rustc-macro-crate.rs

@@ -0,0 +1,24 @@
+// Copyright 2016 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.
+
+// no-prefer-dynamic
+
+#![feature(rustc_macro)]
+#![feature(rustc_macro_lib)]
+#![crate_type = "rustc-macro"]
+
+extern crate rustc_macro;
+
+use rustc_macro::TokenStream;
+
+#[rustc_macro_derive(Foo)]
+pub fn foo(input: TokenStream) -> TokenStream {
+    input
+}