add documentation on howto build just rustc without libstd to the build system

diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 495d7e46baa6ebbf4239ccd42a96f7c1658ed94d..60935770781817a63c3ea9b6a19260ee33118b54 100644 (file)
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -108,7 +108,8 @@ root.
 There are large number of options accepted by this script to alter the
 configuration used later in the build process. Some options to note:
 
 There are large number of options accepted by this script to alter the
 configuration used later in the build process. Some options to note:
 

-- `--enable-debug` - Build a debug version of the compiler (disables optimizations)
+- `--enable-debug` - Build a debug version of the compiler (disables optimizations,
+    which speeds up compilation of stage1 rustc)

 - `--enable-optimize` - Enable optimizations (can be used with `--enable-debug`
     to make a debug build with optimizations)
 - `--disable-valgrind-rpass` - Don't run tests with valgrind
 - `--enable-optimize` - Enable optimizations (can be used with `--enable-debug`
     to make a debug build with optimizations)
 - `--disable-valgrind-rpass` - Don't run tests with valgrind


@@ -128,6 +129,12 @@ Some common make targets are:
   cases we don't need to build the stage2 compiler, so we can save time by not
   building it. The stage1 compiler is a fully functioning compiler and
   (probably) will be enough to determine if your change works as expected.
   cases we don't need to build the stage2 compiler, so we can save time by not
   building it. The stage1 compiler is a fully functioning compiler and
   (probably) will be enough to determine if your change works as expected.

+- `make $host/stage1/bin/rustc` - Where $host is a target triple like x86_64-unknown-linux-gnu.
+  This will build just rustc, without libstd. This is the fastest way to recompile after
+  you changed only rustc source code. Note however that the resulting rustc binary
+  won't have a stdlib to link against by default. You can build libstd once with
+  `make rustc-stage1`, rustc will pick it up afterwards. libstd is only guaranteed to
+  work if recompiled, so if there are any issues recompile it.

 - `make check` - build the full compiler & run all tests (takes a while). This
   is what gets run by the continuous integration system against your pull
   request. You should run this before submitting to make sure your tests pass
 - `make check` - build the full compiler & run all tests (takes a while). This
   is what gets run by the continuous integration system against your pull
   request. You should run this before submitting to make sure your tests pass

diff --git a/Makefile.in b/Makefile.in
index 7425e9bd73e95913b75af6d7b8d345a05218b819..20e2e19305e1b98a34f5a073b490b29267085571 100644 (file)
--- a/Makefile.in
+++ b/Makefile.in
@@ -62,6 +62,8 @@
 #   * tidy - Basic style check, show highest rustc error code and
 #     the status of language and lib features
 #   * rustc-stage$(stage) - Only build up to a specific stage
 #   * tidy - Basic style check, show highest rustc error code and
 #     the status of language and lib features
 #   * rustc-stage$(stage) - Only build up to a specific stage

+#   * $host/stage1/bin/rustc - Only build stage1 rustc, not libstd. For further
+#     information see "Rust recipes for build system success" below.

 #
 # Then mix in some of these environment variables to harness the
 # ultimate power of The Rust Build System.
 #
 # Then mix in some of these environment variables to harness the
 # ultimate power of The Rust Build System.


@@ -93,6 +95,15 @@
 #     // Modifying libstd? Use this command to run unit tests just on your change
 #     make check-stage1-std NO_REBUILD=1 NO_BENCH=1
 #
 #     // Modifying libstd? Use this command to run unit tests just on your change
 #     make check-stage1-std NO_REBUILD=1 NO_BENCH=1
 #

+#     // Modifying just rustc?
+#     // Compile rustc+libstd once
+#     make rustc-stage1
+#     // From now on use this command to rebuild just rustc and reuse the previously built libstd
+#     // $host is a target triple, eg. x86_64-unknown-linux-gnu
+#     // The resulting binary is located at $host/stage1/bin/rustc.
+#     // If there are any issues with libstd recompile it with the command above.
+#     make $host/stage1/bin/rustc
+#

 #     // Added a run-pass test? Use this to test running your test
 #     make check-stage1-rpass TESTNAME=my-shiny-new-test
 #
 #     // Added a run-pass test? Use this to test running your test
 #     make check-stage1-rpass TESTNAME=my-shiny-new-test
 #