Add microfactory to bootstrap a go program with minimal overhead

microfactory is a tool to incrementally compile a go program. It's
similar to `go install`, but doesn't require a GOPATH. A package->path
mapping can be specified as command line options. All input files are
hashed, and if any change, the necessary packages will be rebuilt.

microfactory can (re)build itself as necessary, so combined with a shell
script that runs `go run microfactory.go` the first time, it can
bootstrap a go program entirely from sources with just a working goroot.

Time to build soong_ui only using source & GOROOT:

            first time    no-change incremental
microfactory  1400ms               15ms
go install     670ms              130ms

While microfactory takes longer the first time, almost half of that time
is from `go run` and building microfactory for use later. If
microfactory only has to build soong_ui, it's about 580ms.

Test: USE_SOONG_UI=true m -j blueprint_tools
Test: go test -bench . build/soong/cmd/microfactory/microfactory_test.go
Change-Id: I4d2b9825788144fa10042bbd804482e44f459a54

1 files changed, 101 insertions, 0 deletions

diff --git a/soong_ui.bash b/soong_ui.bash
new file mode 100755
index 00000000..724d9c54
--- /dev/null
+++ b/soong_ui.bash
@@ -0,0 +1,101 @@
+#!/bin/bash -eu
+#
+# Copyright 2017 Google Inc. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# To track how long we took to startup. %N isn't supported on Darwin, but
+# that's detected in the Go code, and skip calculating the startup time.
+export TRACE_BEGIN_SOONG=$(date +%s%N)
+
+# Function to find top of the source tree (if $TOP isn't set) by walking up the
+# tree.
+function gettop
+{
+    local TOPFILE=build/soong/root.bp
+    if [ -z "${TOP-}" -a -f "${TOP-}/${TOPFILE}" ] ; then
+        # The following circumlocution ensures we remove symlinks from TOP.
+        (cd $TOP; PWD= /bin/pwd)
+    else
+        if [ -f $TOPFILE ] ; then
+            # The following circumlocution (repeated below as well) ensures
+            # that we record the true directory name and not one that is
+            # faked up with symlink names.
+            PWD= /bin/pwd
+        else
+            local HERE=$PWD
+            T=
+            while [ \( ! \( -f $TOPFILE \) \) -a \( $PWD != "/" \) ]; do
+                \cd ..
+                T=`PWD= /bin/pwd -P`
+            done
+            \cd $HERE
+            if [ -f "$T/$TOPFILE" ]; then
+                echo $T
+            fi
+        fi
+    fi
+}
+
+# Bootstrap microfactory from source if necessary and use it to build the
+# soong_ui binary, then run soong_ui.
+function run_go
+{
+    # Increment when microfactory changes enough that it cannot rebuild itself.
+    # For example, if we use a new command line argument that doesn't work on older versions.
+    local mf_version=1
+
+    local mf_src="${TOP}/build/soong/cmd/microfactory"
+
+    local out_dir="${OUT_DIR:-${TOP}/out}"
+    local mf_bin="${out_dir}/microfactory_$(uname)"
+    local mf_version_file="${out_dir}/.microfactory_$(uname)_version"
+    local soong_ui_bin="${out_dir}/soong_ui"
+    local from_src=1
+
+    if [ -f "${mf_bin}" ] && [ -f "${mf_version_file}" ]; then
+        if [ "${mf_version}" -eq "$(cat "${mf_version_file}")" ]; then
+            from_src=0
+        fi
+    fi
+
+    local mf_cmd
+    if [ $from_src -eq 1 ]; then
+        mf_cmd="${GOROOT}/bin/go run ${mf_src}/microfactory.go"
+    else
+        mf_cmd="${mf_bin}"
+    fi
+
+    ${mf_cmd} -s "${mf_src}" -b "${mf_bin}" \
+            -pkg-path "android/soong=${TOP}/build/soong" -trimpath "${TOP}/build/soong" \
+            -o "${soong_ui_bin}" android/soong/cmd/soong_ui
+
+    if [ $from_src -eq 1 ]; then
+        echo "${mf_version}" >"${mf_version_file}"
+    fi
+
+    exec "${out_dir}/soong_ui" "$@"
+}
+
+export TOP=$(gettop)
+case $(uname) in
+    Linux)
+        export GOROOT="${TOP}/prebuilts/go/linux-x86/"
+        ;;
+    Darwin)
+        export GOROOT="${TOP}/prebuilts/go/darwin-x86/"
+        ;;
+    *) echo "unknown OS:" $(uname) >&2 && exit 1;;
+esac
+
+run_go "$@"