feat(core): allow disabling modules, services, tests + tasks in confi…

…gs (#1515)

* feat(core): allow disabling modules, services, tests + tasks in configs

This adds an optional `disabled` boolean field to all modules, and
where applicable to service, task and test config schemas.

The semantics are explained both in docs and unit tests, but they are
as follows:

- Disabling a module disables all services, tasks and tests within it.
- A disabled module may still be built if it is a build dependency of
  another module.
- Disabled services are never deployed and are ignored if listed as
  runtime dependencies.
- Disabled tasks are never run and are ignored if listed as
  runtime dependencies.
- Disabled tests are never run.
- An error if throw if trying to explicitly run a service, task or test
  via `garden run ...`, unless the `--force` flag is set.

docs/module-types/conftest.md

@@ -38,45 +38,50 @@ name:
 
 description:
 
-# Specify a list of POSIX-style paths or globs that should be regarded as the source files for
-# this
-# module. Files that do *not* match these paths or globs are excluded when computing the version
-# of the module,
+# Set this to `true` to disable the module. You can use this with conditional template strings to
+# disable modules based on, for example, the current environment or other variables (e.g.
+# `disabled: \${environment.name == "prod"}`). This can be handy when you only need certain modules for
+# specific environments, e.g. only for development.
+#
+# Disabling a module means that any services, tasks and tests contained in it will not be deployed or run.
+# It also means that the module is not built _unless_ it is declared as a build dependency by another enabled
+# module (in which case building this module is necessary for the dependant to be built).
+#
+# If you disable the module, and its services, tasks or tests are referenced as _runtime_ dependencies, Garden
+# will automatically ignore those dependency declarations. Note however that template strings referencing the
+# module's service or task outputs (i.e. runtime outputs) will fail to resolve when the module is disabled,
+# so you need to make sure to provide alternate values for those if you're using them, using conditional
+# expressions.
+disabled: false
+
+# Specify a list of POSIX-style paths or globs that should be regarded as the source files for this
+# module. Files that do *not* match these paths or globs are excluded when computing the version of the module,
 # when responding to filesystem watch events, and when staging builds.
 #
-# Note that you can also _exclude_ files using the `exclude` field or by placing `.gardenignore`
-# files in your
+# Note that you can also _exclude_ files using the `exclude` field or by placing `.gardenignore` files in your
 # source tree, which use the same format as `.gitignore` files. See the
 # [Configuration Files
-# guide](https://docs.garden.io/guides/configuration-files#including-excluding-files-and-directories)
-# for details.
+# guide](https://docs.garden.io/guides/configuration-files#including-excluding-files-and-directories) for details.
 #
 # Also note that specifying an empty list here means _no sources_ should be included.
 include:
 
-# Specify a list of POSIX-style paths or glob patterns that should be excluded from the module.
-# Files that
-# match these paths or globs are excluded when computing the version of the module, when
-# responding to filesystem
+# Specify a list of POSIX-style paths or glob patterns that should be excluded from the module. Files that
+# match these paths or globs are excluded when computing the version of the module, when responding to filesystem
 # watch events, and when staging builds.
 #
-# Note that you can also explicitly _include_ files using the `include` field. If you also specify
-# the
-# `include` field, the files/patterns specified here are filtered from the files matched by
-# `include`. See the
+# Note that you can also explicitly _include_ files using the `include` field. If you also specify the
+# `include` field, the files/patterns specified here are filtered from the files matched by `include`. See the
 # [Configuration Files
-# guide](https://docs.garden.io/guides/configuration-files#including-excluding-files-and-directories)for
-# details.
+# guide](https://docs.garden.io/guides/configuration-files#including-excluding-files-and-directories)for details.
 #
-# Unlike the `modules.exclude` field in the project config, the filters here have _no effect_ on
-# which files
-# and directories are watched for changes. Use the project `modules.exclude` field to affect
-# those, if you have
+# Unlike the `modules.exclude` field in the project config, the filters here have _no effect_ on which files
+# and directories are watched for changes. Use the project `modules.exclude` field to affect those, if you have
 # large directories that should not be watched for changes.
 exclude:
 
-# A remote repository URL. Currently only supports git servers. Must contain a hash suffix
-# pointing to a specific branch or tag, with the format: <git remote url>#<branch|tag>
+# A remote repository URL. Currently only supports git servers. Must contain a hash suffix pointing to a specific
+# branch or tag, with the format: <git remote url>#<branch|tag>
 #
 # Garden will import the repository source code into this module, but read the module's
 # config from the local garden.yml file.
@@ -95,8 +100,7 @@ build:
       copy:
         # POSIX-style path or filename of the directory or file(s) to copy to the target.
         - source:
-          # POSIX-style path or filename to copy the directory or file(s), relative to the build
-          # directory.
+          # POSIX-style path or filename to copy the directory or file(s), relative to the build directory.
           # Defaults to to same as source path.
           target: ''
 
@@ -112,8 +116,7 @@ policyPath:
 # The policy namespace in which to find _deny_ and _warn_ rules.
 namespace: main
 
-# A list of files to test with the given policy. Must be POSIX-style paths, and may include
-# wildcards.
+# A list of files to test with the given policy. Must be POSIX-style paths, and may include wildcards.
 files:
 ```
 
@@ -167,6 +170,27 @@ name: "my-sweet-module"
 | -------- | -------- |
 | `string` | No       |
 
+#### `disabled`
+
+Set this to `true` to disable the module. You can use this with conditional template strings to
+disable modules based on, for example, the current environment or other variables (e.g.
+`disabled: \${environment.name == "prod"}`). This can be handy when you only need certain modules for
+specific environments, e.g. only for development.
+
+Disabling a module means that any services, tasks and tests contained in it will not be deployed or run.
+It also means that the module is not built _unless_ it is declared as a build dependency by another enabled
+module (in which case building this module is necessary for the dependant to be built).
+
+If you disable the module, and its services, tasks or tests are referenced as _runtime_ dependencies, Garden
+will automatically ignore those dependency declarations. Note however that template strings referencing the
+module's service or task outputs (i.e. runtime outputs) will fail to resolve when the module is disabled,
+so you need to make sure to provide alternate values for those if you're using them, using conditional
+expressions.
+
+| Type      | Required | Default |
+| --------- | -------- | ------- |
+| `boolean` | No       | `false` |
+
 #### `include`
 
 Specify a list of POSIX-style paths or globs that should be regarded as the source files for this