feat: support extending a parent environment

Adds a new environment configuration to bin/hermit.hcl
```
inherit-parent = true
```

Setting this inherits the Hermit environment from a parent directory, inheriting environment variables and packages.

This should be useful in larger monorepos where we want to have a single root environment with most tooling, but want to still allow subprojects to have their own owerwrites and environment variables.

Note, the packages in parent environment won't have access to the child environment even when being called from the child environment. This means that any package calling another package in the parent environment will still call the parent package even if that is overwritten in the child environment. Though this can be potentially confusing, it should give more consistent behaviour between parent and child environments. Also, package dependencies can not cross environments. So, it is not possible to have a package dependency from a child environment package to a parent environment package.

Finally, for the time being, all hermit operations apply only to the currently active environment. So, it is not possible to upgrade or uninstall parent packages from the child environment, for example

docs/docs/usage/config.md

@@ -7,11 +7,12 @@ customise that Hermit environment.
 
 ## Attributes
 
-| Attribute | Type | Description |
-|-----------|------|-------------|
-| `env` | `{string:string}?` | Extra environment variables. |
-| `sources` | `[string]?` | Package manifest sources in order of preference. |
-| `manage-git` | `bool?` | Whether Hermit should manage Git. |
+| Attribute | Type | Description                                                                           |
+|-----------|------|---------------------------------------------------------------------------------------|
+| `env` | `{string:string}?` | Extra environment variables.                                                          |
+| `sources` | `[string]?` | Package manifest sources in order of preference.                                      |
+| `manage-git` | `bool?` | Whether Hermit should manage Git.                                                     |
+| `inherit-parent` | `bool?` | Whether this Hermit environment should inherit an environment from a parent diectory. | 
 
 ## Per-environment Sources
 

env.go

@@ -87,10 +87,11 @@ 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."`
-	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"`
+	AddIJPlugin   bool          `hcl:"idea,optional" default:"false" help:"Whether Hermit should automatically add the IntelliJ IDEA plugin."`
 }
 
 // Env is a Hermit environment.
@@ -974,11 +975,27 @@ func (e *Env) Envars(l *ui.UI, inherit bool) ([]string, error) {
 // environment variables defined in the packages installed in the environment,
 // and finally any environment variables explicitly configured in the environment.
 func (e *Env) EnvOps(l *ui.UI) (envars.Ops, error) {
+	var ops envars.Ops
+
+	if e.config.InheritParent {
+		// load EnvOps from a potential parent environment first
+		parent, err := e.openParent()
+		if err != nil {
+			return nil, err
+		}
+		if parent != nil {
+			ops, err = parent.EnvOps(l)
+			if err != nil {
+				return nil, err
+			}
+		}
+	}
+
 	pkgs, err := e.ListInstalled(l)
 	if err != nil {
 		return nil, err
 	}
-	return e.allEnvarOpsForPackages(nil, nil, pkgs...), nil
+	return append(ops, e.allEnvarOpsForPackages(nil, nil, pkgs...)...), nil
 }
 
 // SetEnv sets an extra environment variable.
@@ -1433,6 +1450,27 @@ func (e *Env) resolver(l *ui.UI) (*manifest.Resolver, error) {
 	return resolver, nil
 }
 
+// openParent finds the closest hermit Env from the parent directories of this Env.
+// if no such environment was found, returns nil
+func (e *Env) openParent() (*Env, error) {
+	path, err := filepath.Abs(e.envDir)
+	if err != nil {
+		return nil, err
+	}
+	for {
+		path = filepath.Dir(path)
+		if path == "/" {
+			// we are at the root of the filesystem, no hermit environments found
+			return nil, nil
+		}
+		if _, err := os.Stat(filepath.Join(path, "bin", "activate-hermit")); err == nil {
+			return OpenEnv(path, e.state, e.packageSource, nil, e.httpClient, e.scriptSums)
+		} else if !errors.Is(err, os.ErrNotExist) {
+			return nil, err
+		}
+	}
+}
+
 // tidySha256Db is a helper function to remove leading and trailing
 // whitespaces and empty lines from a multiline string containing
 // SHA-256 hash digests, and return a slice of digest strings that do

integration/integration_test.go

@@ -274,6 +274,22 @@ func TestIntegration(t *testing.T) {
 			. env2/bin/activate-hermit
 			assert test "$FOO" = "BAR"
 			`},
+		{name: "InheritsEnvVariables",
+			preparations: prep{fixture("environment_inheritance"), activate("child_environment")},
+			script:       `echo "${OVERWRITTEN} - ${NOT_OVERWRITTEN}"`,
+			expectations: exp{outputContains("child - parent")},
+		},
+		{name: "InheritanceOverwritesBinaries",
+			preparations: prep{fixture("environment_inheritance"), activate(".")},
+			script: `
+			hermit install binary
+			. child_environment/bin/activate-hermit
+			assert test "$(binary.sh)" = "Running from parent"
+			
+			hermit install binary
+			assert test "$(binary.sh)" = "Running from child"
+			`,
+		},
 	}
 
 	checkForShells(t)

integration/testdata/environment_inheritance/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/environment_inheritance/bin/activate-hermit

@@ -0,0 +1,21 @@
+#!/bin/bash
+# This file must be used with "source bin/activate-hermit" from bash or zsh.
+# You cannot run it directly
+#
+# THIS FILE IS GENERATED; DO NOT MODIFY
+
+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/environment_inheritance/bin/hermit

@@ -0,0 +1,43 @@
+#!/bin/bash
+#
+# THIS FILE IS GENERATED; DO NOT MODIFY
+
+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/environment_inheritance/bin/hermit.hcl

@@ -0,0 +1,2 @@
+sources = ["env:///packages"]
+env = { OVERWRITTEN:parent, NOT_OVERWRITTEN:parent }

integration/testdata/environment_inheritance/child_environment/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/environment_inheritance/child_environment/bin/activate-hermit

@@ -0,0 +1,21 @@
+#!/bin/bash
+# This file must be used with "source bin/activate-hermit" from bash or zsh.
+# You cannot run it directly
+#
+# THIS FILE IS GENERATED; DO NOT MODIFY
+
+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/environment_inheritance/child_environment/bin/hermit

@@ -0,0 +1,43 @@
+#!/bin/bash
+#
+# THIS FILE IS GENERATED; DO NOT MODIFY
+
+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/environment_inheritance/child_environment/bin/hermit.hcl

@@ -0,0 +1,3 @@
+sources = ["env:///packages"]
+inherit-parent = true
+env = { OVERWRITTEN:child }

integration/testdata/environment_inheritance/child_environment/packages/binary.hcl

@@ -0,0 +1,4 @@
+description = "binary"
+source = "${env}/packages/binary.sh"
+binaries = ["binary.sh"]
+version "1.0.1" {}

integration/testdata/environment_inheritance/child_environment/packages/binary.sh

@@ -0,0 +1,3 @@
+#!/usr/bin/env bash
+
+echo "Running from child"

integration/testdata/environment_inheritance/packages/binary.hcl

@@ -0,0 +1,4 @@
+description = "binary"
+source = "${env}/packages/binary.sh"
+binaries = ["binary.sh"]
+version "1.0.0" {}

integration/testdata/environment_inheritance/packages/binary.sh

@@ -0,0 +1,3 @@
+#!/usr/bin/env bash
+
+echo "Running from parent"