Add option not to override existing env variables

README.md

@@ -34,3 +34,9 @@ Pipenv env var | Poetry env var
 -------------- | ----------------------
 PIPENV_DOTENV_LOCATION | POETRY_DOTENV_LOCATION
 PIPENV_DONT_LOAD_ENV | POETRY_DONT_LOAD_ENV
+
+### Overriding existing environment variables
+
+By default, this plugin will override existing environment variables. This is because this plugin was built to make onboarding for users coming from `pipenv` as seamless as possible. If you want to prevent existing environment variables from being overridden, you can set the `POETRY_DOTENV_DONT_OVERRIDE` environment variable to `true`.[^1]
+
+[^1]: See [#16](https://github.com/mpeteuil/poetry-dotenv-plugin/pull/16) for background.

poetry_dotenv_plugin/dotenv_plugin.py

@@ -29,4 +29,9 @@ def load_dotenv(
             io.write_line("<debug>Loading environment variables.</debug>")
 
         path = POETRY_DOTENV_LOCATION or dotenv.find_dotenv(usecwd=True)
-        dotenv.load_dotenv(dotenv_path=path, override=True)
+        POETRY_DOTENV_DONT_OVERRIDE = os.environ.get("POETRY_DOTENV_DONT_OVERRIDE", "")
+        DOTENV_OVERRIDE = not POETRY_DOTENV_DONT_OVERRIDE.lower() in (
+            "true",
+            "1",
+        )
+        dotenv.load_dotenv(dotenv_path=path, override=DOTENV_OVERRIDE)

tests/test_system.sh

@@ -56,6 +56,46 @@ function test_end_to_end_system_with_dotenv_location_override() {
   fi
 }
 
+function test_end_to_end_system_with_default_env_overrides() {
+  # Setup
+  local expected
+  expected='foo'
+  create_dotenv_file
+
+  local output
+  output=$(export MY_ENV_VAR='bar' && poetry run python -c "import os; print(os.environ['MY_ENV_VAR'])")
+
+  # Cleanup
+  delete_dotenv_file
+
+  if [ "$expected" = "$output" ]; then
+    printf "test_end_to_end_system_with_default_env_overrides: PASSED\n"
+  else
+    printf "Expected '$expected', but got '%s'.\n" "$output"
+    exit 1
+  fi
+}
+
+function test_end_to_end_system_without_env_overrides() {
+  # Setup
+  local expected
+  expected='bar'
+  create_dotenv_file
+
+  local output
+  output=$(export MY_ENV_VAR='bar' POETRY_DOTENV_DONT_OVERRIDE=true && poetry run python -c "import os; print(os.environ['MY_ENV_VAR'])")
+
+  # Cleanup
+  delete_dotenv_file
+
+  if [ "$expected" = "$output" ]; then
+    printf "test_end_to_end_system_without_env_overrides: PASSED\n"
+  else
+    printf "Expected '$expected', but got '%s'.\n" "$output"
+    exit 1
+  fi
+}
+
 function test_end_to_end_system_without_loading_dotenv_file() {
   # Setup
   local expected
@@ -78,4 +118,6 @@ function test_end_to_end_system_without_loading_dotenv_file() {
 
 test_end_to_end_system_with_default_dotenv_file
 test_end_to_end_system_with_dotenv_location_override
+test_end_to_end_system_with_default_env_overrides
+test_end_to_end_system_without_env_overrides
 test_end_to_end_system_without_loading_dotenv_file