Avoid unnecessary operations when using lock

poetry/console/commands/lock.py

@@ -27,7 +27,6 @@ the current directory, processes it, and locks the depdencies in the <comment>po
             self.poetry.pool,
         )
 
-        installer.update(True)
-        installer.execute_operations(False)
+        installer.lock()
 
         return installer.run()

poetry/installation/installer.py

@@ -47,6 +47,7 @@ class Installer:
         self._dev_mode = True
         self._develop = []
         self._execute_operations = True
+        self._lock = False
 
         self._whitelist = []
 
@@ -111,6 +112,16 @@ class Installer:
 
         return self
 
+    def lock(self):  # type: () -> Installer
+        """
+        Prepare the installer for locking only.
+        """
+        self.update()
+        self.execute_operations(False)
+        self._lock = True
+
+        return self
+
     def is_updating(self):  # type: () -> bool
         return self._update
 
@@ -182,6 +193,12 @@ class Installer:
 
         self._populate_local_repo(local_repo, ops, locked_repository)
 
+        if self._lock:
+            # If we are only in lock mode, no need to go any further
+            self._write_lock_file(local_repo)
+
+            return 0
+
         root = self._package
         if not self.is_dev_mode():
             root = root.clone()
@@ -273,19 +290,20 @@ class Installer:
             )
 
         # Writing lock before installing
+        self._write_lock_file(local_repo)
+
+        self._io.writeln("")
+        for op in ops:
+            self._execute(op)
+
+    def _write_lock_file(self, repo):  # type: (Repository) -> None
         if self._update and self._write_lock:
-            updated_lock = self._locker.set_lock_data(
-                self._package, local_repo.packages
-            )
+            updated_lock = self._locker.set_lock_data(self._package, repo.packages)
 
             if updated_lock:
                 self._io.writeln("")
                 self._io.writeln("<info>Writing lock file</>")
 
-        self._io.writeln("")
-        for op in ops:
-            self._execute(op)
-
     def _execute(self, operation):  # type: (Operation) -> None
         """
         Execute a given operation.