Add install-on-activate to eagerly install selected packages on env activation (#559)

Hermit packages are normally downloaded on-demand when a stub binary in
`./bin` is first invoked. This causes problems for packages like openjdk
that export environment variables pointing to the package root (e.g.
`JAVA_HOME`). Tools like Gradle, Android Studio, and `gradlew` read
`JAVA_HOME` directly and run `$JAVA_HOME/bin/java` without going through
hermit stubs — if the JDK hasn't been downloaded yet, that path doesn't
exist and the tools fail.

This adds an `install-on-activate` list to `bin/hermit.hcl` that
specifies which packages should be eagerly downloaded and unpacked when
the environment is activated:

```hcl
install-on-activate = ["openjdk"]
```

Only the listed packages are installed eagerly; everything else remains
lazy. This keeps activation fast for environments with many packages
while ensuring critical ones like the JDK are always present.

Author: joshfriend

app/activate_cmd.go

@@ -35,6 +35,9 @@ func (a *activateCmd) Run(l *ui.UI, cache *cache.Cache, sta *state.State, global
 	if err != nil {
 		return errors.WithStack(err)
 	}
+	if err := env.EnsureInstalled(l); err != nil {
+		return errors.WithStack(err)
+	}
 	messages, err := env.Trigger(l, manifest.EventEnvActivate)
 	if err != nil {
 		return errors.WithStack(err)

env.go

@@ -90,11 +90,12 @@ const (
 
 // Config for a Hermit environment.
 type Config struct {
-	Envars        envars.Envars `hcl:"env,optional" help:"Extra environment variables."`
-	Sources       []string      `hcl:"sources,optional" help:"Package manifest sources."`
-	ManageGit     bool          `hcl:"manage-git,optional" default:"true" help:"Whether Hermit should automatically 'git add' new packages."`
-	InheritParent bool          `hcl:"inherit-parent,optional" default:"false" help:"Whether this environment inherits a potential parent environment from one of the parent directories"`
-	AddIJPlugin   bool          `hcl:"idea,optional" default:"false" help:"Whether Hermit should automatically add the IntelliJ IDEA plugin."`
+	Envars            envars.Envars `hcl:"env,optional" help:"Extra environment variables."`
+	Sources           []string      `hcl:"sources,optional" help:"Package manifest sources."`
+	ManageGit         bool          `hcl:"manage-git,optional" default:"true" help:"Whether Hermit should automatically 'git add' new packages."`
+	InheritParent     bool          `hcl:"inherit-parent,optional" default:"false" help:"Whether this environment inherits a potential parent environment from one of the parent directories"`
+	InstallOnActivate []string      `hcl:"install-on-activate,optional" help:"List of packages to eagerly download and unpack when the environment is activated."`
+	AddIJPlugin       bool          `hcl:"idea,optional" default:"false" help:"Whether Hermit should automatically add the IntelliJ IDEA plugin."`
 
 	GitHubTokenAuth GitHubTokenAuthConfig `hcl:"github-token-auth,block" help:"When to use GitHub token authentication."`
 }
@@ -431,6 +432,31 @@ next:
 	return nil
 }
 
+// EnsureInstalled downloads and unpacks packages listed in
+// install-on-activate when the environment is activated.
+func (e *Env) EnsureInstalled(l *ui.UI) error {
+	if len(e.config.InstallOnActivate) == 0 {
+		return nil
+	}
+	wanted := map[string]bool{}
+	for _, name := range e.config.InstallOnActivate {
+		wanted[name] = true
+	}
+	pkgs, err := e.ListInstalled(l)
+	if err != nil {
+		return errors.WithStack(err)
+	}
+	for _, pkg := range pkgs {
+		if !wanted[pkg.Reference.Name] {
+			continue
+		}
+		if err := e.state.CacheAndUnpack(l.Task(pkg.Reference.String()), pkg); err != nil {
+			return errors.WithStack(err)
+		}
+	}
+	return nil
+}
+
 // Trigger an event for all installed packages.
 func (e *Env) Trigger(l *ui.UI, event manifest.Event) (messages []string, err error) {
 	pkgs, err := e.ListInstalled(l)

integration/integration_test.go

@@ -673,6 +673,21 @@ EOF
 				assert test "${CLEANUP_DONE:-}" = "yes"
 			`,
 		},
+		{
+			name:         "InstallOnActivateEnsuresPackagesAreUnpacked",
+			preparations: prep{fixture("testenv-install-on-activate"), activate(".")},
+			script: `
+			with-prompt-hooks hermit install testbin1
+			# Clean extracted packages to simulate a fresh clone where
+			# stubs exist but the package hasn't been unpacked yet.
+			hermit clean --packages
+			assert test ! -d "${TESTBIN1_ROOT}"
+			# Re-activate; install-on-activate should re-download/unpack.
+			. bin/activate-hermit
+			assert test -d "${TESTBIN1_ROOT}"
+			assert test -x "${TESTBIN1_ROOT}/testbin1"
+			`,
+		},
 	}
 
 	checkForShells(t)

integration/testdata/testenv-install-on-activate/bin/README.hermit.md

@@ -0,0 +1,7 @@
+# Hermit environment
+
+This is a [Hermit](https://github.com/cashapp/hermit) bin directory.
+
+The symlinks in this directory are managed by Hermit and will automatically
+download and install Hermit itself as well as packages. These packages are
+local to this environment.

integration/testdata/testenv-install-on-activate/bin/activate-hermit

@@ -0,0 +1,19 @@
+#!/bin/bash
+# This file must be used with "source bin/activate-hermit" from bash or zsh.
+# You cannot run it directly
+
+if [ "${BASH_SOURCE-}" = "$0" ]; then
+  echo "You must source this script: \$ source $0" >&2
+  exit 33
+fi
+
+BIN_DIR="$(dirname "${BASH_SOURCE[0]:-${(%):-%x}}")"
+if "${BIN_DIR}/hermit" noop > /dev/null; then
+  eval "$("${BIN_DIR}/hermit" activate "${BIN_DIR}/..")"
+
+  if [ -n "${BASH-}" ] || [ -n "${ZSH_VERSION-}" ]; then
+      hash -r 2>/dev/null
+    fi
+
+    echo "Hermit environment $("${HERMIT_ENV}"/bin/hermit env HERMIT_ENV) activated"
+fi

integration/testdata/testenv-install-on-activate/bin/hermit

@@ -0,0 +1,41 @@
+#!/bin/bash
+
+set -eo pipefail
+
+export HERMIT_USER_HOME=~
+
+if [ -z "${HERMIT_STATE_DIR}" ]; then
+  case "$(uname -s)" in
+  Darwin)
+    export HERMIT_STATE_DIR="${HERMIT_USER_HOME}/Library/Caches/hermit"
+    ;;
+  Linux)
+    export HERMIT_STATE_DIR="${XDG_CACHE_HOME:-${HERMIT_USER_HOME}/.cache}/hermit"
+    ;;
+  esac
+fi
+
+export HERMIT_DIST_URL="${HERMIT_DIST_URL:-https://github.com/cashapp/hermit/releases/download/stable}"
+HERMIT_CHANNEL="$(basename "${HERMIT_DIST_URL}")"
+export HERMIT_CHANNEL
+export HERMIT_EXE=${HERMIT_EXE:-${HERMIT_STATE_DIR}/pkg/hermit@${HERMIT_CHANNEL}/hermit}
+
+if [ ! -x "${HERMIT_EXE}" ]; then
+  echo "Bootstrapping ${HERMIT_EXE} from ${HERMIT_DIST_URL}" 1>&2
+  INSTALL_SCRIPT="$(mktemp)"
+  # This value must match that of the install script
+  INSTALL_SCRIPT_SHA256="180e997dd837f839a3072a5e2f558619b6d12555cd5452d3ab19d87720704e38"
+  if [ "${INSTALL_SCRIPT_SHA256}" = "BYPASS" ]; then
+    curl -fsSL "${HERMIT_DIST_URL}/install.sh" -o "${INSTALL_SCRIPT}"
+  else
+    # Install script is versioned by its sha256sum value
+    curl -fsSL "${HERMIT_DIST_URL}/install-${INSTALL_SCRIPT_SHA256}.sh" -o "${INSTALL_SCRIPT}"
+    # Verify install script's sha256sum
+    openssl dgst -sha256 "${INSTALL_SCRIPT}" | \
+      awk -v EXPECTED="$INSTALL_SCRIPT_SHA256" \
+      '$2!=EXPECTED {print "Install script sha256 " $2 " does not match " EXPECTED; exit 1}'
+  fi
+  /bin/bash "${INSTALL_SCRIPT}" 1>&2
+fi
+
+exec "${HERMIT_EXE}" --level=fatal exec "$0" -- "$@"

integration/testdata/testenv-install-on-activate/bin/hermit.hcl

@@ -0,0 +1,2 @@
+sources = ["env:///packages"]
+install-on-activate = ["testbin1"]

integration/testdata/testenv-install-on-activate/packages/testbin1.hcl

@@ -0,0 +1,9 @@
+description = "Test package one"
+env = {
+  FOO: "bar",
+  TESTBIN1VERSION: "${version}",
+  TESTBIN1_ROOT: "${root}",
+}
+source = "${env}/packages/testbin1.tgz"
+binaries = ["testbin1"]
+version "1.0.0" "1.0.1" {}