Merge pull request 'Put GOPATH/bin on PATH so go install-ed tools run' (#6) from container-gopath-bin into main

Reviewed-on: #6

Dockerfile

@@ -7,6 +7,13 @@ FROM ${REGISTRY}/${BASE_IMAGE_NAME}:${BASE_VERSION} AS image
 ARG DISTRO=alma9
 ARG GO_CACHE_PLUGIN_VERSION=v0.1.0
 ARG GO_CACHE_PLUGIN_SHA256=0eb23d06a0dcf395559cb6447864579c220e60148fdcd6a6f841c2b17169b9b8
+# `go install` writes to $GOPATH/bin, which nothing puts on PATH by default, so an
+# installed tool is not runnable. Match the official golang images: GOPATH out of root's
+# home, its bin on PATH, and world-writable so this still works if the image ever runs
+# as non-root.
+ENV GOPATH=/go
+ENV PATH=/go/bin:$PATH
+
 COPY distros/${DISTRO}/ /tmp/distro/
 # DL3041: versions are pinned by the estate dnf repos, not here. SC2086: $PACKAGES is a
 # word list on purpose. DL4006: the only pipe ends in sha256sum, whose status is the
@@ -20,5 +27,7 @@ RUN set -eux; \
       "https://git.unkin.net/unkin/go-cache-plugin/releases/download/${GO_CACHE_PLUGIN_VERSION}/go-cache-plugin-linux-amd64"; \
     echo "$GO_CACHE_PLUGIN_SHA256  /usr/local/bin/go-cache-plugin" | sha256sum -c -; \
     chmod 0755 /usr/local/bin/go-cache-plugin; \
+    mkdir -p "$GOPATH/bin"; \
+    chmod -R 1777 "$GOPATH"; \
     rm -rf /var/cache/dnf /tmp/distro
 CMD ["/bin/bash"]

README.md

@@ -13,6 +13,9 @@ Adds `golang`, `gcc` and `nfpm`, and bakes in the `go-cache-plugin` binary on `P
 so Go pipelines get the shared build cache with no download step. No credentials and no
 `GOCACHEPROG` value are baked in — consumers set those.
 
+`GOPATH` is `/go` with `/go/bin` on `PATH`, as on the official `golang` images, so a tool
+installed with `go install <tool>@<version>` is runnable by name in the same step.
+
 The `container-base` release this image builds on is `BASE_VERSION` in the `Dockerfile`.
 
 ## Adding a distro