Add "tip" version

This is pinned to the latest commit merged upstream before midnight (UTC) on Monday of the current week.

Dockerfile-linux.template

@@ -13,7 +13,15 @@ FROM buildpack-deps:{{ env.variant }}-scm AS build
 
 ENV PATH /usr/local/go/bin:$PATH
 
+{{ if env.version != "tip" then ( -}}
 ENV GOLANG_VERSION {{ .version }}
+{{ ) else ( -}}
+COPY --from=golang:{{ env.variant }} /usr/local/go /usr/local/goroot-bootstrap
+
+# {{ .version }}: https://github.com/golang/go/tree/{{ .commit.version }}
+ARG GOLANG_COMMIT={{ .commit.version | @sh }}
+ENV GOLANG_COMMIT $GOLANG_COMMIT
+{{ ) end -}}
 
 {{
 	def os_arches:
@@ -54,16 +62,23 @@ RUN set -eux; \
 	now="$(date '+%s')"; \
 {{ if is_alpine then ( -}}
 	apk add --no-cache --virtual .fetch-deps \
+{{ if env.version != "tip" then ( -}}
 		ca-certificates \
 		gnupg \
 # busybox's "tar" doesn't handle directory mtime correctly, so our SOURCE_DATE_EPOCH lookup doesn't work (the mtime of "/usr/local/go" always ends up being the extraction timestamp)
 		tar \
+{{ ) else ( -}}
+		bash \
+		git \
+{{ ) end -}}
 	; \
 	arch="$(apk --print-arch)"; \
 {{ ) else ( -}}
 	arch="$(dpkg --print-architecture)"; arch="${arch##*-}"; \
 {{ ) end -}}
+{{ if env.version != "tip" then ( -}}
 	url=; \
+{{ ) else "" end -}}
 	case "$arch" in \
 {{
 	[
@@ -78,8 +93,12 @@ RUN set -eux; \
 		| (
 -}}
 		{{ $osArch | @sh }}) \
+{{ if env.version != "tip" then ( -}}
 			url={{ .url | @sh }}; \
 			sha256={{ .sha256 | @sh }}; \
+{{ ) else ( -}}
+			export {{ .env | to_entries | sort_by(.key) | map(.key + "=" + (.value | @sh)) | join(" ") }}; \
+{{ ) end -}}
 			;; \
 {{
 		)
@@ -88,6 +107,7 @@ RUN set -eux; \
 		*) echo >&2 "error: unsupported architecture '$arch' (likely packaging update needed)"; exit 1 ;; \
 	esac; \
 	\
+{{ if env.version != "tip" then ( -}}
 	wget -O go.tgz.asc "$url.asc"; \
 	wget -O go.tgz "$url"{{ if is_alpine then "" else " --progress=dot:giga" end }}; \
 	echo "$sha256 *go.tgz" | sha256sum -c -; \
@@ -107,14 +127,57 @@ RUN set -eux; \
 	\
 # save the timestamp from the tarball so we can restore it for reproducibility, if necessary (see below)
 	SOURCE_DATE_EPOCH="$(stat -c '%Y' /usr/local/go)"; \
+{{ ) else ( -}}
+# before we get too far, let's validate that our "bootstrap" Go works
+	export GOROOT_BOOTSTRAP=/usr/local/goroot-bootstrap; \
+# TODO figure out why QEMU's user-mode emulation with Go 1.23.0 causes "can't start telemetry child process: fork/exec /usr/local/go/bin/go: invalid argument" (it works if we run it a second time, but then later "go build" fails to fork/exec the compile process 🙃)
+	"$GOROOT_BOOTSTRAP/bin/go" version; \
+	\
+	git init --quiet /usr/local/go; \
+	git -C /usr/local/go fetch --depth 1 https://github.com/golang/go.git "$GOLANG_COMMIT:"; \
+	git -C /usr/local/go checkout --quiet FETCH_HEAD; \
+	\
+# save the Git timestamp so we can use it for reproducibility
+	SOURCE_DATE_EPOCH="$(git -C /usr/local/go log -1 --format='format:%ct' HEAD)"; \
+{{ ) end -}}
 	export SOURCE_DATE_EPOCH; \
 	touchy="$(date -d "@$SOURCE_DATE_EPOCH" '+%Y%m%d%H%M.%S')"; \
 # for logging validation/edification
 	date --date "@$SOURCE_DATE_EPOCH" --rfc-2822; \
 # sanity check (detected value should be older than our wall clock)
 	[ "$SOURCE_DATE_EPOCH" -lt "$now" ]; \
 	\
-{{ if .arches["arm32v7"].url // "" | contains("armv6") then ( -}}
+{{ if env.version == "tip" then ( -}}
+	( \
+		export \
+			GOCACHE='/tmp/gocache' \
+# set GOHOST* to make sure explicitly 32bit builds on 64bit infra work correctly
+			GOHOSTOS="$GOOS" \
+			GOHOSTARCH="$GOARCH" \
+		; \
+		\
+		cd /usr/local/go/src; \
+		./make.bash; \
+		\
+# remove a few intermediate / bootstrapping files the official binary release tarballs do not contain (and ".git" that is hard to make reproducible)
+		rm -rf \
+			/usr/local/go/.git* \
+			/usr/local/go/pkg/*/cmd \
+			/usr/local/go/pkg/bootstrap \
+			/usr/local/go/pkg/obj \
+			/usr/local/go/pkg/tool/*/api \
+			/usr/local/go/pkg/tool/*/go_bootstrap \
+			/usr/local/go/src/cmd/dist/dist \
+			"$GOCACHE" \
+		; \
+		\
+# clamp timestamps for reproducibility (allows "COPY --link" to be more clever/useful)
+		touch -t "$touchy" /usr/local/.go-date-stamp; \
+		find /usr/local/go -depth -newer /usr/local/.go-date-stamp -exec touch -ht "$touchy" '{}' +; \
+		rm /usr/local/.go-date-stamp; \
+	); \
+	\
+{{ ) elif .arches["arm32v7"].url // "" | contains("armv6") then ( -}}
 	if [ "$arch" = {{ os_arches["arm32v7"] | @sh }} ]; then \
 		[ -s /usr/local/go/go.env ]; \
 		before="$(go env GOARM)"; [ "$before" != {{ .arches["arm32v7"].env["GOARM"] | @sh }} ]; \
@@ -166,8 +229,10 @@ RUN set -eux; \
 	rm -rf /var/lib/apt/lists/*
 {{ ) end -}}
 
+{{ if env.version != "tip" then ( -}}
 ENV GOLANG_VERSION {{ .version }}
 
+{{ ) else "" end -}}
 # don't auto-upgrade the gotoolchain
 # https://github.com/docker-library/golang/issues/472
 ENV GOTOOLCHAIN=local

generate-stackbrew-library.sh

@@ -111,8 +111,6 @@ for version; do
 
 		fullVersion="$(jq -r '.[env.version].version' versions.json)"
 
-		[[ "$fullVersion" == *.*[^0-9]* ]] || fullVersion+='.0'
-
 		if [ "$version" = "$fullVersion" ]; then
 			baseAliases=( "${versionAliases[@]}" )
 		else