feat: add --no-hash option to update, preventing metadata.content-hash

Currently when creating a lockfile, a metadata.content-hash field is
generated, containing the hash of the sorted contents of pyproject.toml.

However (see python-poetry#496) this causes merge conflicts, particularly
when using a tool such as dependabot that makes multiple parallel
branches with dependency changes.

Add a --no-hash option to poetry update. This causes metadata.content-hash
to be omitted. In turn poetry will later complain that the lock file
may not be fresh, (although it is correct), and the user can run poetry lock
to update it, after all the merges are complete.

dependabot currently runs `poetry update <DEPENDENCY> --lock`, I would
propose to incrporate this PR to poetry and then modify dependabot
to have teh --no-hash option.

docs/docs/cli.md

@@ -166,6 +166,7 @@ update the constraint, for example `^2.3`. You can do this using the `add` comma
 * `--dry-run` : Outputs the operations but will not execute anything (implicitly enables --verbose).
 * `--no-dev` : Do not install dev dependencies.
 * `--lock` : Do not perform install (only update the lockfile).
+* `--no-hash` : Do not write a content-hash to the lockfile. Useful with merge conflics.
 
 ## add
 

poetry/console/commands/update.py

@@ -23,6 +23,7 @@ class UpdateCommand(EnvCommand):
             "(implicitly enables --verbose).",
         ),
         option("lock", None, "Do not perform operations (only update the lockfile)."),
+        option("no-hash", None, "Do not write a content-hash to the lockfile."),
     ]
 
     loggers = ["poetry.repositories.pypi_repository"]
@@ -41,6 +42,7 @@ def handle(self):
 
         installer.dev_mode(not self.option("no-dev"))
         installer.dry_run(self.option("dry-run"))
+        self.poetry.locker.set_write_hash(not self.option("no-hash"))
         installer.execute_operations(not self.option("lock"))
 
         # Force update

poetry/packages/locker.py

@@ -27,6 +27,7 @@ def __init__(self, lock, local_config):  # type: (Path, dict) -> None
         self._local_config = local_config
         self._lock_data = None
         self._content_hash = self._get_content_hash()
+        self._write_hash = True
 
     @property
     def lock(self):  # type: () -> TomlFile
@@ -184,6 +185,8 @@ def set_lock_data(self, root, packages):  # type: (...) -> bool
             "content-hash": self._content_hash,
             "files": files,
         }
+        if not self._write_hash:
+            del lock["metadata"]["content-hash"]
 
         if not self.is_locked() or lock != self.lock_data:
             self._write_lock_data(lock)
@@ -201,6 +204,9 @@ def _write_lock_data(self, data):
 
         self._lock_data = None
 
+    def set_write_hash(self, write_hash=True):
+        self._write_hash = write_hash
+
     def _get_content_hash(self):  # type: () -> str
         """
         Returns the sha256 hash of the sorted content of the pyproject file.

tests/console/conftest.py

@@ -93,6 +93,7 @@ def __init__(self, lock, local_config):
         self._locked = False
         self._lock_data = None
         self._write = False
+        self._write_hash = True
 
     def write(self, write=True):
         self._write = write

tests/installation/test_installer.py

@@ -44,6 +44,7 @@ def __init__(self):
         self._written_data = None
         self._locked = False
         self._content_hash = self._get_content_hash()
+        self._write_hash = True
 
     @property
     def written_data(self):

tests/utils/test_exporter.py

@@ -14,6 +14,7 @@ class Locker(BaseLocker):
     def __init__(self):
         self._locked = True
         self._content_hash = self._get_content_hash()
+        self._write_hash = True
 
     def locked(self, is_locked=True):
         self._locked = is_locked