Better UX error for migrations (#7966)

* Better UX error for migrations

Signed-off-by: Uilian Ries <uilianries@gmail.com>

* File already exists is not an error

Signed-off-by: Uilian Ries <uilianries@gmail.com>

* Print dir path name for makedirs error

Signed-off-by: Uilian Ries <uilianries@gmail.com>

* Fix cache attribute

Signed-off-by: Uilian Ries <uilianries@gmail.com>

* Run migration test

Signed-off-by: Uilian Ries <uilianries@gmail.com>

* Fix expected string

Signed-off-by: Uilian Ries <uilianries@gmail.com>

* Improve migration error message

Signed-off-by: Uilian Ries <uilianries@gmail.com>

* Filter error message for utils.file.save

Signed-off-by: Uilian Ries <uilianries@gmail.com>

* Exclude errno.ENOENT from file errors

Signed-off-by: Uilian Ries <uilianries@gmail.com>

* Could not apply chmod on Windows

There is a note on chmod docs:
https://docs.python.org/2.7/library/os.html#os.chmod

"Although Windows supports chmod(), you can only set the file’s
read-only flag with it (via the stat.S_IWRITE and stat.S_IREAD constants
or a corresponding integer value). All other bits are ignored."

However, it works for files, not for folder.

Signed-off-by: Uilian Ries <uilianries@gmail.com>

conans/migrations.py

@@ -32,8 +32,9 @@ def _make_migrations(self, old_version):
     def _update_version_file(self):
         try:
             save(self.file_version_path, str(self.current_version))
-        except Exception:
-            raise ConanException("Can't write version file in %s" % self.file_version_path)
+        except Exception as error:
+            raise ConanException("Can't write version file in '{}': {}"
+                                 .format(self.file_version_path, str(error)))
 
     def _load_old_version(self):
         try:

conans/test/unittests/client/migrations/test_migrator.py

@@ -0,0 +1,36 @@
+# coding=utf-8
+
+import unittest
+import os
+import platform
+
+from conans.migrations import Migrator
+from conans.test.utils.mocks import TestBufferConanOutput
+from conans.test.utils.test_files import temp_folder
+from conans.errors import ConanMigrationError
+
+
+class FakeMigrator(Migrator):
+
+    def __init__(self, cache_folder, current_version, out):
+        self.cache_folder = cache_folder
+        super(FakeMigrator, self).__init__(cache_folder, current_version, out)
+
+    def _make_migrations(self, old_version):
+        pass
+
+
+class MigratorPermissionTest(unittest.TestCase):
+
+    @unittest.skipIf(platform.system() == "Windows", "Can't apply chmod on Windows")
+    def test_invalid_permission(self):
+        out = TestBufferConanOutput()
+        conf_path = temp_folder(False)
+        os.chmod(conf_path, 0o444)
+        conf_path = os.path.join(conf_path, "foo")
+        migrator = FakeMigrator(conf_path, "latest", out)
+        with self.assertRaises(ConanMigrationError) as error:
+            migrator.migrate()
+        self.assertEqual("Can't write version file in '{0}/version.txt': The folder {0} does not "
+                         "exist and could not be created (Permission denied).".format(conf_path),
+                         str(error.exception))

conans/util/files.py

@@ -187,10 +187,16 @@ def save(path, content, only_if_modified=False, encoding="utf-8"):
         only_if_modified: file won't be modified if the content hasn't changed
         encoding: target file text encoding
     """
-    try:
-        os.makedirs(os.path.dirname(path))
-    except Exception:
-        pass
+    dir_path = os.path.dirname(path)
+    if not os.path.isdir(dir_path):
+        try:
+            os.makedirs(dir_path)
+        except OSError as error:
+            if error.errno not in (errno.EEXIST, errno.ENOENT):
+                raise OSError("The folder {} does not exist and could not be created ({})."
+                              .format(dir_path, error.strerror))
+        except Exception:
+            raise
 
     new_content = to_file_bytes(content, encoding)