Add `--only-root` option to install command, excluding all dependencies. (#5783)

* Add `--only-root` option to group commands, excluding all dependencies.
* Add documentation for usage.
* Apply suggestions from code review

Co-authored-by: Bjorn Neergaard <bjorn@neersighted.com>

docs/cli.md

@@ -167,6 +167,12 @@ It's also possible to only install specific dependency groups by using the `only
 poetry install --only test,docs
 ```
 
+To only install the project itself with no dependencies, use the `--only-root` flag.
+
+```bash
+poetry install --only-root
+```
+
 See [Dependency groups]({{< relref "managing-dependencies#dependency-groups" >}}) for more information
 about dependency groups.
 
@@ -220,6 +226,7 @@ option is used.
 * `--without`: The dependency groups to ignore.
 * `--with`: The optional dependency groups to include.
 * `--only`: The only dependency groups to include.
+* `--only-root`: Install only the root project, exclude all dependencies.
 * `--default`: Only include the main dependencies. (**Deprecated**)
 * `--sync`: Synchronize the environment with the locked packages and the specified groups.
 * `--no-root`: Do not install the root package (your project).

docs/managing-dependencies.md

@@ -158,6 +158,15 @@ poetry install --only main
 ```
 {{% /note %}}
 
+{{% note %}}
+If you want to install the project root, and no other dependencies, you can use
+the `--only-root` option.
+
+```bash
+poetry install --only-root
+```
+{{% /note %}}
+
 ### Removing dependencies from a group
 
 The [`remove`]({{< relref "cli#remove" >}}) command supports a `--group` option

src/poetry/console/commands/install.py

@@ -47,6 +47,13 @@ class InstallCommand(InstallerCommand):
             multiple=True,
         ),
         option("all-extras", None, "Install all extra dependencies."),
+        option(
+            "only-root",
+            None,
+            "Exclude all dependencies.",
+            flag=True,
+            multiple=False,
+        ),
     ]
 
     help = """The <info>install</info> command reads the <comment>poetry.lock</> file from
@@ -65,6 +72,13 @@ dependencies and not including the current project, run the command with the
 
     _loggers = ["poetry.repositories.pypi_repository", "poetry.inspection.info"]
 
+    @property
+    def activated_groups(self) -> set[str]:
+        if self.option("only-root"):
+            return set()
+        else:
+            return super().activated_groups
+
     def handle(self) -> int:
         from poetry.core.masonry.utils.module import ModuleOrPackageNotFound
 
@@ -82,6 +96,25 @@ dependencies and not including the current project, run the command with the
             )
             return 1
 
+        if self.option("only-root") and any(
+            self.option(key) for key in {"with", "without", "only"}
+        ):
+            self.line_error(
+                "<error>The `<fg=yellow;options=bold>--with</>`,"
+                " `<fg=yellow;options=bold>--without</>` and"
+                " `<fg=yellow;options=bold>--only</>` options cannot be used with"
+                " the `<fg=yellow;options=bold>--only-root</>`"
+                " option.</error>"
+            )
+            return 1
+
+        if self.option("only-root") and self.option("no-root"):
+            self.line_error(
+                "<error>You cannot specify `<fg=yellow;options=bold>--no-root</>`"
+                " when using `<fg=yellow;options=bold>--only-root</>`.</error>"
+            )
+            return 1
+
         if self.option("all-extras"):
             extras = list(self.poetry.package.extras.keys())
         else:

tests/console/commands/test_install.py

@@ -73,6 +73,7 @@ def tester(
     ("options", "groups"),
     [
         ("", {MAIN_GROUP, "foo", "bar", "baz", "bim"}),
+        ("--only-root", set()),
         (f"--only {MAIN_GROUP}", {MAIN_GROUP}),
         ("--only foo", {"foo"}),
         ("--only foo,bar", {"foo", "bar"}),
@@ -111,7 +112,13 @@ def test_group_options_are_passed_to_the_installer(
     if not with_root:
         options = f"--no-root {options}"
 
-    tester.execute(options)
+    status_code = tester.execute(options)
+
+    if options == "--no-root --only-root":
+        assert status_code == 1
+        return
+    else:
+        assert status_code == 0
 
     package_groups = set(tester.command.poetry.package._dependency_groups.keys())
     installer_groups = set(tester.command.installer._groups)