Ensure vcs dependencies preserve editable flag

Resolves: #3263

poetry/packages/locker.py

@@ -571,7 +571,7 @@ def _dump_package(self, package):  # type: (Package) -> dict
             if package.source_resolved_reference:
                 data["source"]["resolved_reference"] = package.source_resolved_reference
 
-            if package.source_type == "directory":
+            if package.source_type in ["directory", "git"]:
                 data["develop"] = package.develop
 
         return data

poetry/puzzle/provider.py

@@ -168,6 +168,7 @@ def search_for_vcs(self, dependency):  # type: (VCSDependency) -> List[Package]
             rev=dependency.rev,
             name=dependency.name,
         )
+        package.develop = dependency.develop
 
         dependency._constraint = package.version
         dependency._pretty_constraint = package.version.text

tests/packages/test_locker.py

@@ -73,6 +73,7 @@ def test_lock_file_data_is_ordered(locker, root):
 category = "main"
 optional = false
 python-versions = "*"
+develop = true
 
 [package.source]
 type = "git"

tests/puzzle/test_provider.py

@@ -47,6 +47,15 @@ def provider(root, pool):
     return Provider(root, pool, NullIO())
 
 
+@pytest.mark.parametrize("value", [True, False])
+def test_search_for_vcs_retains_develop_flag(provider, value):
+    dependency = VCSDependency(
+        "demo", "git", "https://github.com/demo/demo.git", develop=value
+    )
+    package = provider.search_for_vcs(dependency)[0]
+    assert package.develop == value
+
+
 def test_search_for_vcs_setup_egg_info(provider):
     dependency = VCSDependency("demo", "git", "https://github.com/demo/demo.git")