versioned_go_build.sh

#!/bin/bash

set -euf -o pipefail

# In a nutshell, this script:
# - makes a tempdir and moves to it
# - go gets the requested bin (but does not install it)
# - cds to the repo
# - checks out the requested version
# - maybe runs `glide install`
# - maybe runs `dep ensure`
# - builds the bin and puts it where you told it to.
#
# Since doing that verbatim is a bit noisy, and pinning tools tends to
# cause them to slowly get out of date, it does two additional things:
# - suppresses output unless `--debug` is passed
# - checks for newer commits / tags than the one you passed, and
#   prints the newer sha/version (if any) to stderr so it's always visible.

usage () {
    echo 'Installs a specific version of a go-gettable bin to the specified location.'
    echo ''
    echo 'Usage:'
    echo ''
    echo -e "\\t$0 [--debug] go-gettable-repo version [path-to-bin-in-repo] install-location"
    echo ''
    echo 'Examples:'
    echo ''
    echo -e "\\t$0 go.uber.org/thriftrw 1.10.0 somewhere/thriftrw"
    echo -e '\t\tInstalls v1.10.0 of go.uber.org/thriftrw to somewhere/thriftrw.'
    echo -e '\t\tNotice that go.uber.org/thriftrw is both the repository AND the binary name.'
    echo ''
    echo -e "\\t$0 golang.org/x/lint SOME_SHA golint somewhere/golint"
    echo -e '\t\tInstalls a specific SHA of e.g. "golang.org/x/lint/golint" to "somewhere/golint",'
    echo -e '\t\tNotice that the golint bin is in a subfolder of the golang.org/x/lint repository.'

    exit 1
}

num_commits_behind () {
    head=$1
    git rev-list "..$head" | wc -l | tr -dc '0-9'
}

is_versioned () {
    # returns truthy if the arg is version-like.

    str=$1
    if echo "$str" | grep -q -E "$VERSION_TAG_REGEX"; then
        return 0
    fi
    return 1
}

most_recent_version_tag () {
    # using xargs because it's safer (for big lists) + it doesn't result in
    # a ton of SHAs in debug output like `git describe --tags $(...)` causes.
    #
    # in brief:
    # - get all tagged shas
    # - get their tags
    # - grep for version-like tags
    # - sort by version
    # - return the "biggest"

    git rev-list --tags \
    | xargs git describe --always --tags 2>/dev/null \
    | grep -E "$VERSION_TAG_REGEX" \
    | sort -Vr \
    | head -n 1
}

# matches "v1[.2[.3[.4]]]" exactly or fails.
# this intentionally does not match "v1.2.3-ae83c2" tags, nor "v1.2-pre", etc,
# as these are not likely "real" release versions.
declare -r VERSION_TAG_REGEX='^v?\d+(\.\d+){0,3}$'

# output control vars
declare DEBUG=
declare TO_DEV_NULL=
declare QUIET=

# build control vars
declare -x GOPATH
declare GO_GETTABLE_REPO
declare VERSION
declare GO_GETTABLE_BIN
declare INSTALL_LOCATION

# handle optional debug (and consume the arg)
if [ "$1" == "--debug" ]; then
    shift  # consume it
    DEBUG=1
else
    # otherwise, redirect to /dev/null (requires eval)
    TO_DEV_NULL='>/dev/null'
    # pass quiet flags where needed (do not quote)
    QUIET='--quiet'
fi

# must have 3 or 4 args
[ $# -ge 3 ] || usage
[ $# -le 4 ] || usage

[ -z $DEBUG ] || set -x

#
# Set up some variables / the temp folder
#

# set up gopath, and make sure it's cleaned up regardless of how we exit
GOPATH=$(mktemp -d)
trap 'rm -rf $GOPATH' EXIT

GO_GETTABLE_REPO="$1"
VERSION="$2"
if [ $# -eq 4 ]; then
    # bin resides in a sub-folder
    GO_GETTABLE_BIN="$1/$3"
    INSTALL_LOCATION="$4"
elif [ $# -eq 3 ]; then
    # repo == bin
    GO_GETTABLE_BIN="$1"
    INSTALL_LOCATION="$3"
else
    # should be unreachable
    usage
fi

#
# Pull the repo, set to the correct version
#

# TODO: use go modules
# See:
#  * https://github.com/myitcv/gobin
#  * https://github.com/golang/go/issues/25922
export GO111MODULE=off

go get -d "$GO_GETTABLE_BIN"
# eval so redirection works when quiet
eval "pushd $GOPATH/src/$GO_GETTABLE_REPO $TO_DEV_NULL"

# save for the version check
HEAD="$(git rev-parse HEAD)"

# silently check out, reduces a lot of default spam
git checkout $QUIET "$VERSION"

#
# Check if we're building an old version, warn if so
#

if is_versioned "$VERSION"; then
    # versioned, check for newer tags.
    LATEST="$(most_recent_version_tag)"
    # use sort to check if VERSION >= LATEST, or warn about the newer version
    echo -e "$VERSION\\n$LATEST" | sort -Vrc 2>/dev/null || (>&2 echo -e "\\t$GO_GETTABLE_REPO has a newer tag: $LATEST")
else
    # not versioned, check for newer commits
    BEHIND="$(num_commits_behind "$HEAD")"
    # should be zero, or warn about the newer version
    [ "$BEHIND" -eq 0 ] || (>&2 echo -e "\\t$GO_GETTABLE_REPO is $BEHIND commits behind the current HEAD: $HEAD")
fi

#
# Build the bin, install to the correct location
#

# only glide install when there is a glide file, or it tries to install
# to the current repo (not in our current folder)
if [ -f glide.lock ]; then
    glide $QUIET install
fi
if [ -f Gopkg.lock ]; then
    dep init
fi

# eval so redirection works when quiet
eval "popd $TO_DEV_NULL"

go build -o "$INSTALL_LOCATION" "$GO_GETTABLE_BIN"