Fix errors when git could not be found

CHANGELOG.md

@@ -32,6 +32,7 @@
 - Fixed detection of `.egg-info` directory for non-poetry projects. (Thanks to [@gtors](https://github.com/gtors))
 - Fixed only-wheel builds. (Thanks to [@gtors](https://github.com/gtors))
 - Fixed key and array order in lock file to avoid having differences when relocking.
+- Fixed errors when `git` could not be found.
 
 
 ## [0.10.3] - 2018-06-04

poetry/vcs/__init__.py

+import subprocess
+import warnings
+
 from poetry.utils._compat import Path
 
 from .git import Git
@@ -8,4 +11,12 @@ def get_vcs(directory):  # type: (Path) -> Git
 
     for p in [directory] + list(directory.parents):
         if (p / ".git").is_dir():
-            return Git(p)
+            try:
+                return Git(p)
+            except (subprocess.CalledProcessError, OSError):
+                # Either git could not be found or does not exist
+                warnings.warn(
+                    "git executable could not be found", category=RuntimeWarning
+                )
+
+                return

poetry/vcs/git.py

@@ -7,7 +7,7 @@ from poetry.utils._compat import decode
 
 
 class GitConfig:
-    def __init__(self):
+    def __init__(self, requires_git_presence=False):
         self._config = {}
 
         try:
@@ -22,7 +22,8 @@ class GitConfig:
                 for group in m:
                     self._config[group[0]] = group[1]
         except (subprocess.CalledProcessError, OSError):
-            pass
+            if requires_git_presence:
+                raise
 
     def get(self, key, default=None):
         return self._config.get(key, default)
@@ -33,7 +34,7 @@ class GitConfig:
 
 class Git:
     def __init__(self, work_dir=None):
-        self._config = GitConfig()
+        self._config = GitConfig(requires_git_presence=True)
         self._work_dir = work_dir
 
     @property