(minor) Add fetch depth option

docs/modules/ROOT/pages/grgit-fetch.adoc

@@ -13,7 +13,7 @@ grgit.fetch()
 
 [source, groovy]
 ----
-grgit.fetch(remote: '<name or uri>', refSpecs: [<refspec>, ...], prune: <boolean>, tagMode: <mode>)
+grgit.fetch(remote: '<name or uri>', refSpecs: [<refspec>, ...], prune: <boolean>, depth: <int>, tagMode: <mode>)
 ----
 
 [source, groovy]
@@ -22,6 +22,7 @@ grgit.fetch {
   remote = '<name or uri>'
   refspecs = [<refspec>, ...]
   prune = <boolean>
+  depth = <int>
   tagMode = <mode>
 }
 ----
@@ -43,6 +44,7 @@ The format of a <refspec> parameter is an optional plus +, followed by the sourc
 +
 The remote ref that matches <src> is fetched, and if <dst> is not empty string, the local ref that matches it is fast-forwarded using <src>. If the optional plus + is used, the local ref is updated even if it does not result in a fast-forward update.
 prune:: (`boolean`, default `false`) Before fetching, remove any remote-tracking references that no longer exist on the remote. Tags are not subject to pruning if they are fetched only because of the default tag auto-following or due to a `tagMode` option. However, if tags are fetched due to an explicit refspec, then they are also subject to pruning.
+depth: (`Integer`, default `null`) If set, limits fetching to the specified number of commits from the tip each remote branch history
 tagMode:: (`String`, default `auto`) Must be one of `'auto'`, `'all'`, `'none'`.
 +
 `'auto'` - tags that point at objects that are downloaded from the remote repository are fetched and stored locally.

grgit-core/src/main/groovy/org/ajoberstar/grgit/operation/FetchOp.groovy

@@ -35,6 +35,11 @@ class FetchOp implements Callable<Void> {
    */
   boolean prune = false
 
+  /**
+   * The depth of the clone. Defaults to full history.
+   */
+  Integer depth = null
+
   /**
    * How should tags be handled.
    */
@@ -58,6 +63,7 @@ class FetchOp implements Callable<Void> {
     cmd.refSpecs = refSpecs.collect { new RefSpec(it) }
     cmd.removeDeletedRefs = prune
     cmd.tagOpt = tagMode.jgit
+    if (depth) { cmd.depth = depth }
     cmd.call()
     return null
   }

grgit-core/src/test/groovy/org/ajoberstar/grgit/operation/FetchOpSpec.groovy

@@ -3,9 +3,7 @@ package org.ajoberstar.grgit.operation
 import org.ajoberstar.grgit.Grgit
 import org.ajoberstar.grgit.fixtures.GitTestUtil
 import org.ajoberstar.grgit.fixtures.MultiGitOpSpec
-import org.ajoberstar.grgit.operation.FetchOp.TagMode
 import org.eclipse.jgit.api.errors.GitAPIException
-
 import spock.lang.Unroll
 
 class FetchOpSpec extends MultiGitOpSpec {
@@ -106,4 +104,16 @@ class FetchOpSpec extends MultiGitOpSpec {
       'refs/remotes/origin/master',
       'refs/remotes/origin/my-branch']
   }
+
+  def 'fetch with depth does a shallow fetch'() {
+    given:
+    def shallowGrgit = init('shallow')
+    shallowGrgit.remote.add(name: 'origin', url: remoteGrgit.repository.rootDir.toURI())
+    when:
+    shallowGrgit.fetch(remote: 'origin', depth: 1)
+    shallowGrgit.checkout(branch: 'master', createBranch: true, startPoint: 'origin/master')
+    then:
+    shallowGrgit.head().id == remoteGrgit.resolve.toCommit('master').id
+    shallowGrgit.head().parentIds.isEmpty()
+  }
 }