Check for the existence of git before running commands.

Checks in the gclient wrapper and when running any gclient git command.

TEST=none
BUG=none

Patch contributed by Nasser <nasser@codeaurora>

Review URL: http://codereview.chromium.org/518064

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@35762 0039d316-1c4b-4281-b951-d872f2087c98

gclient

@@ -7,14 +7,48 @@
 
 base_dir=$(dirname "$0")
 
+# Test git and git --version.
+function test_git {
+  local GITV="$(git --version)" || {
+    echo "git isn't installed, please install it"
+    exit 1
+  }
+
+  GITV="${GITV##* }"          # Only examine last word (i.e. version number)
+  local GITD=( ${GITV//./ } ) # Split version number into decimals
+  if ((GITD[0] < 1 || (GITD[0] == 1 && GITD[1] < 6) )); then
+    echo "git version is ${GITV}, please update to a version later than 1.6"
+    exit 1
+  fi
+}
+
+# Test git svn and git svn --version.
+function test_git_svn {
+  local GITV="$(git svn --version)" || {
+    echo "git-svn isn't installed, please install it"
+    exit 1
+  }
+
+  GITV="${GITV#* version }"   # git svn --version has extra output to remove.
+  GITV="${GITV% (svn*}"
+  local GITD=( ${GITV//./ } ) # Split version number into decimals
+  if ((GITD[0] < 1 || (GITD[0] == 1 && GITD[1] < 6) )); then
+    echo "git version is ${GITV}, please update to a version later than 1.6"
+    exit 1
+  fi
+}
+
+
 # Update git checkouts prior the cygwin check, we don't want to use msysgit.
 if [ "X$DEPOT_TOOLS_UPDATE" != "X0" -a -e "$base_dir/.git" ]
 then
+  test_git_svn
   (cd "$base_dir"; git svn rebase -q -q)
 fi
 
 if [ "X$DEPOT_TOOLS_UPDATE" != "X0" -a -e "$base_dir/git-cl-repo/.git" ]
 then
+  test_git
   (cd "$base_dir/git-cl-repo"; git pull -q)
 fi
 

gclient_scm.py

@@ -286,8 +286,13 @@ class GitWrapper(SCMWrapper, scm.GIT):
       cwd = self.checkout_path
     cmd = [self.COMMAND]
     cmd.extend(args)
-    sp = subprocess.Popen(cmd, cwd=cwd, stdout=stdout)
-    output = sp.communicate()[0]
+    logging.debug(cmd)
+    try:
+      sp = subprocess.Popen(cmd, cwd=cwd, stdout=stdout)
+      output = sp.communicate()[0]
+    except OSError:
+      raise gclient_utils.Error("git command '%s' failed to run." %
+              ' '.join(cmd) + "\nCheck that you have git installed.")
     if checkrc and sp.returncode:
       raise gclient_utils.Error('git command %s returned %d' %
                                 (args[0], sp.returncode))