Protobuf: update build instructions for MinGW

See https://github.com/bazelbuild/bazel/issues/1856

Slightly reformat (prettify) the page too.

--
MOS_MIGRATED_REVID=134649252

1 files changed, 45 insertions, 16 deletions

diff --git a/third_party/protobuf/README.md b/third_party/protobuf/README.md
index bf93a9893d..0c7627c8d0 100644
--- a/third_party/protobuf/README.md
+++ b/third_party/protobuf/README.md
@@ -1,4 +1,4 @@
-How to update the binaries other than `protoc-linux-x86_64.exe`:
+### Updating binaries other than the Linux 64-bit and MinGW ones
 
 1. Go to http://search.maven.org/
 2. Search for g:"com.google.protobuf"
@@ -9,35 +9,64 @@ How to update the binaries other than `protoc-linux-x86_64.exe`:
 7. Update `third_party/BUILD` to point to the new jar file.
 8. Done.
 
+* * *
+### Updating the Linux 64-bit proto compiler
 The 64-bit Linux version of the proto compiler is linked statically. To update it, do
 the following steps on an x86_64 machine:
 
 1. `git clone http://github.com/google/protobuf.git`
-2. `git checkout <commithash>` (current is `d5fb408d` or `3.0.0-beta-2`)
+2. `git checkout <tag or commithash>` (e.g. `v3.0.0` or `e8ae137`)
 3. `./autogen.sh`
 4. `LDFLAGS=-static ./configure`
 5. Change `LDFLAGS = -static` to `LDFLAGS = -all-static` in  `src/Makefile`.
 6. `make`
 7. `cp src/protoc <Bazel tree>/third_party/protobuf/protoc-linux-x86_64.exe` .
 
-How to update `protobuf.bzl` and the `src/` directory:
+* * *
+### Updating the MinGW proto compiler (64-bit)
+Do this from a MinGW shell ([https://sourceforge.net/projects/msys2/files/]) on
+a Windows machine.
+
+1. Clone the protobuf repo and check out the right commit
+
+   ```sh
+   git clone http://github.com/google/protobuf.git
+   git checkout <tag or commithash>   # e.g. `v3.0.0` or `e8ae137`
+   ```
+
+2. Close all other MSYS/MinGW/Cygwin windows. Kill all running background jobs.
+   This step is optional, but if you have other terminal windows open the next
+   step may print some error messages (though it still seems to work).
+3. Install necessary MinGW packages
+
+   ```sh
+   pacman -Syuu autoconf automake libtool curl make gcc unzip
+   ```
+
+4. Configure for static linking and build like you would for Unix
+
+   ```sh
+   ./autogen.sh
+   ./configure --disable-shared   # takes about 2 minutes
+   ./make                         # takes about 11 minutes
+   ```
+
+5. Copy resulting binary
+
+   ```sh
+   cp src/protoc.exe <bazel tree>/third_party/protobuf/protoc-mingw.exe
+   ```
+
+* * *
+### Updating `protobuf.bzl` and the `src/` directory:
 
 1. `git clone http://github.com/google/protobuf.git`
-2. `git checkout <commithash>` (current is `d5fb408d` or `3.0.0-beta-2`)
+2. `git checkout <tag or commithash>` (e.g. `v3.0.0` or `e8ae137`)
 2. `mkdir -p third_party/protobuf/src/google` in the root of the Bazel tree.
 3. `cp -R <root of protobuf tree>/src/google/protobuf third_party/protobuf/src/google`
 4. Update rules in `third_party/protobuf/BUILD` with the rules in the protobuf repository.
 5. Done.
 
-How to update `protoc-mingw.exe`:
-This is pretty much the same steps as for x86_64 above, but they need to be done
-from MingW shell on Windows machine ([https://sourceforge.net/projects/msys2/files/]).
-
-1. `git clone http://github.com/google/protobuf.git`
-2. `git checkout <commithash>` (current is `d5fb408d` or `3.0.0-beta-2`)
-3. `./autogen.sh`
-6. `make`
-7. `cp src/protoc.exe <Bazel tree>/third_party/protobuf/protoc-mingw.exe` .
-
-How to update anything else in this directory: follow usual procedure as described on
-https://www.bazel.io/contributing.html
+* * *
+### Updating anything else in the directory
+Follow usual procedure as described on https://www.bazel.io/contributing.html