Allow "commit" option to describe a module containing commit functi…

…ons (#768)

* Add CommitFunctions and update config with defaults

* Add changeset

* add checks and types for new commit option

* moved default to cli

* update tests

* fix build

* rename commit fns

* add option for skipCI

* update tests

* move commit logic to cli

* update tests for commit

* allow disabling commit for only one of add/version

* update docs

* update tests

* Apply suggestions from code review

Co-authored-by: Mateusz Burzyński <mateuszburzynski@gmail.com>

* remove unnecessary partial

* change option name

* Apply suggestions from code review

Co-authored-by: Mateusz Burzyński <mateuszburzynski@gmail.com>

* Small tweaks after review

* Tweak changesets

Co-authored-by: Mateusz Burzyński <mateuszburzynski@gmail.com>

.changeset/rare-meals-switch.md

@@ -0,0 +1,5 @@
+---
+"@changesets/types": major
+---
+
+`commit` properties of config types were adjusted to account for this option potentially pointing to a module path.

.changeset/stupid-dogs-eat.md

@@ -0,0 +1,5 @@
+---
+"@changesets/cli": minor
+---
+
+Allow `"commit"` option to be more configurable. You can now point to a module (using a module name or a relative path) that might contain `getAddMessage` and/or `getVersionMessage`. This allows you to configure how the commit message is generated, if `[skip ci]` gets included, etc.

.changeset/tough-rivers-decide.md

@@ -0,0 +1,5 @@
+---
+"@changesets/apply-release-plan": major
+---
+
+This module is no longer responsible for commiting files - this responsibility has been moved entirely to `@changesets/cli`.

.changeset/yellow-cows-juggle.md

@@ -0,0 +1,5 @@
+---
+"@changesets/config": major
+---
+
+The parsed config now normalzied the commit option to either `false` or a tuple describing what module should be loaded to resolve commit functions.

docs/config-file-options.md

@@ -16,9 +16,30 @@ Changesets has a minimal amount of configuration options. Mostly these are for w
 
 > NOTE: the `linked`, `updateInternalDependencies`, and `ignore` options are only for behaviour in monorepos.
 
-## `commit` (`true` | `false`)
+## `commit` (`boolean`, or module path as a `string`, or a tuple like `[modulePath: string, options: any]`)
 
-This argument sets whether the `changeset add` command and the `changeset publish` command will also add and commit the changed files using git. By default, we do not commit the files, and leave it to the user to commit the files.
+This option is for setting if the `changeset add` command and the `changeset version` commands will also add and commit the changed files using git, and how the commit messages should be generated for them.
+
+By default, we do not commit the files, and leave it to the user to commit the files. If it is `true`, we use the default commit message generator (`["@changesets/cli/commit", { "skipCI": "version" }]`). Setting it to a string and options tuple specifies a path from where we will load the commit message generation functions. It expects to be a file that exports one or both of the following:
+
+```
+{
+  getAddMessage,
+  getVersionMessage
+}
+```
+
+If one of the methods is not present then we will not commit the files changed for that command.
+
+You would specify a custom commit message generator with:
+
+```json
+{
+  "commit": ["../scripts/commit.js", { "customOption": true }]
+}
+```
+
+This is similar to how the [changelog generator functions work](#changelog-false-or-a-path).
 
 ## `access` (`restricted` | `public`)