Ensure develop flag is respected for git packages (#1321)

Resolves: #1080

poetry/installation/pip_installer.py

@@ -138,10 +138,15 @@ class PipInstaller(BaseInstaller):
             return req
 
         if package.source_type == "git":
-            return "git+{}@{}#egg={}".format(
+            req = "git+{}@{}#egg={}".format(
                 package.source_url, package.source_reference, package.name
             )
 
+            if package.develop:
+                req = ["-e", req]
+
+            return req
+
         return "{}=={}".format(package.name, package.version)
 
     def create_temporary_requirement(self, package):
@@ -226,6 +231,6 @@ class PipInstaller(BaseInstaller):
         pkg = Package(package.name, package.version)
         pkg.source_type = "directory"
         pkg.source_url = str(src_dir)
-        pkg.develop = True
+        pkg.develop = package.develop
 
         self.install_directory(pkg)

tests/installation/test_pip_installer.py

+import pytest
+
 from poetry.installation.pip_installer import PipInstaller
 from poetry.io import NullIO
 from poetry.packages.package import Package
 from poetry.utils.env import NullEnv
 
 
-def test_requirement():
-    installer = PipInstaller(NullEnv(), NullIO())
+@pytest.fixture
+def package_git():
+    package = Package("demo", "1.0.0")
+    package.source_type = "git"
+    package.source_url = "git@github.com:demo/demo.git"
+    package.source_reference = "master"
+    return package
+
+
+@pytest.fixture
+def installer():
+    return PipInstaller(NullEnv(), NullIO())
 
+
+def test_requirement(installer):
     package = Package("ipython", "7.5.0")
     package.hashes = [
         "md5:dbdc53e3918f28fa335a173432402a00",
@@ -22,3 +36,19 @@ def test_requirement():
     )
 
     assert expected == result
+
+
+def test_requirement_git_develop_false(installer, package_git):
+    package_git.develop = False
+    result = installer.requirement(package_git)
+    expected = "git+git@github.com:demo/demo.git@master#egg=demo"
+
+    assert expected == result
+
+
+def test_requirement_git_develop_true(installer, package_git):
+    package_git.develop = True
+    result = installer.requirement(package_git)
+    expected = ["-e", "git+git@github.com:demo/demo.git@master#egg=demo"]
+
+    assert expected == result