Document the --fork-strategy setting (#9887)

crates/uv-cli/src/lib.rs

@@ -4052,9 +4052,9 @@ pub struct ToolUpgradeArgs {
     /// supported Python version (`requires-python`), while minimizing the number of selected
     /// versions across platforms.
     ///
-    /// Under `fewest`, uv will minimize the number of
-    /// selected versions for each package, preferring older versions that are compatible with a
-    /// wider range of supported Python versions or platforms.
+    /// Under `fewest`, uv will minimize the number of selected versions for each package,
+    /// preferring older versions that are compatible with a wider range of supported Python
+    /// versions or platforms.
     #[arg(
         long,
         value_enum,
@@ -4859,9 +4859,9 @@ pub struct ResolverArgs {
     /// supported Python version (`requires-python`), while minimizing the number of selected
     /// versions across platforms.
     ///
-    /// Under `fewest`, uv will minimize the number of
-    /// selected versions for each package, preferring older versions that are compatible with a
-    /// wider range of supported Python versions or platforms.
+    /// Under `fewest`, uv will minimize the number of selected versions for each package,
+    /// preferring older versions that are compatible with a wider range of supported Python
+    /// versions or platforms.
     #[arg(
         long,
         value_enum,
@@ -5049,9 +5049,9 @@ pub struct ResolverInstallerArgs {
     /// supported Python version (`requires-python`), while minimizing the number of selected
     /// versions across platforms.
     ///
-    /// Under `fewest`, uv will minimize the number of
-    /// selected versions for each package, preferring older versions that are compatible with a
-    /// wider range of supported Python versions or platforms.
+    /// Under `fewest`, uv will minimize the number of selected versions for each package,
+    /// preferring older versions that are compatible with a wider range of supported Python
+    /// versions or platforms.
     #[arg(
         long,
         value_enum,

crates/uv-settings/src/settings.rs

@@ -493,9 +493,9 @@ pub struct ResolverInstallerOptions {
     /// supported Python version (`requires-python`), while minimizing the number of selected
     /// versions across platforms.
     ///
-    /// Under `fewest`, uv will minimize the number of
-    /// selected versions for each package, preferring older versions that are compatible with a
-    /// wider range of supported Python versions or platforms.
+    /// Under `fewest`, uv will minimize the number of selected versions for each package,
+    /// preferring older versions that are compatible with a wider range of supported Python
+    /// versions or platforms.
     #[option(
         default = "\"fewest\"",
         value_type = "str",
@@ -1095,9 +1095,9 @@ pub struct PipOptions {
     /// supported Python version (`requires-python`), while minimizing the number of selected
     /// versions across platforms.
     ///
-    /// Under `fewest`, uv will minimize the number of
-    /// selected versions for each package, preferring older versions that are compatible with a
-    /// wider range of supported Python versions or platforms.
+    /// Under `fewest`, uv will minimize the number of selected versions for each package,
+    /// preferring older versions that are compatible with a wider range of supported Python
+    /// versions or platforms.
     #[option(
         default = "\"fewest\"",
         value_type = "str",

docs/concepts/resolution.md

@@ -88,7 +88,7 @@ This ensures that dependencies are locked for everyone working on the project, r
 operating system, architecture, and Python version. The uv lockfile is created and modified by
 [project](../concepts/projects/index.md) commands such as `uv lock`, `uv sync`, and `uv add`.
 
-universal resolution is also available in uv's pip interface, i.e.,
+Universal resolution is also available in uv's pip interface, i.e.,
 [`uv pip compile`](../pip/compile.md), with the `--universal` flag. The resulting requirements file
 will contain markers to indicate which platform each dependency is relevant for.
 
@@ -97,12 +97,6 @@ if different versions are needed for different platforms — the markers determi
 be used. A universal resolution is often more constrained than a platform-specific resolution, since
 we need to take the requirements for all markers into account.
 
-During universal resolution, a minimum Python version must be specified. Project commands read the
-minimum required version from `project.requires-python` in the `pyproject.toml`. When using uv's pip
-interface, provide a value with the `--python-version` option; otherwise, the current Python version
-will be treated as a lower bound. For example, `--universal --python-version 3.9` performs a
-universal resolution for Python 3.9 and later.
-
 During universal resolution, all selected dependency versions must be compatible with the _entire_
 `requires-python` range declared in the `pyproject.toml`. For example, if a project's
 `requires-python` is `>=3.8`, then uv will not allow _any_ dependency versions that are limited to,
@@ -229,6 +223,40 @@ _intentionally_ limited and requires user opt-in for pre-releases to ensure corr
 For more details, see
 [Pre-release compatibility](../pip/compatibility.md#pre-release-compatibility).
 
+## Multi-version resolution
+
+During universal resolution, a package may be listed multiple times with different versions or URLs
+within the same lockfile, since different versions may be needed for different platforms or Python
+versions.
+
+The `--fork-strategy` setting can be used to control how uv trades off between (1) minimizing the
+number of selected versions and (2) selecting the latest-possible version for each platform. The
+former leads to greater consistency across platforms, while the latter leads to use of newer package
+versions where possible.
+
+By default (`--fork-strategy requires-python`), uv will optimize for selecting the latest version of
+each package for each supported Python version, while minimizing the number of selected versions
+across platforms.
+
+For example, when resolving `numpy` with a Python requirement of `>=3.8`, uv would select the
+following versions:
+
+```txt
+numpy==1.24.4 ; python_version == "3.8"
+numpy==2.0.2 ; python_version == "3.9"
+numpy==2.2.0 ; python_version >= "3.10"
+```
+
+This resolution reflects the fact that NumPy 2.2.0 and later require at least Python 3.10, while
+earlier versions are compatible with Python 3.8 and 3.9.
+
+Under `--fork-strategy fewest`, uv will instead minimize the number of selected versions for each
+package, preferring older versions that are compatible with a wider range of supported Python
+versions or platforms.
+
+For example, when in the scenario above, uv would select `numpy==1.24.4` for all Python versions,
+rather than upgrading to `numpy==2.0.2` for Python 3.9 and `numpy==2.2.0` for Python 3.10 and later.
+
 ## Dependency constraints
 
 Like pip, uv supports constraint files (`--constraint constraints.txt`) which narrow the set of

docs/reference/settings.md

@@ -773,9 +773,9 @@ By default, uv will optimize for selecting the latest version of each package fo
 supported Python version (`requires-python`), while minimizing the number of selected
 versions across platforms.
 
-Under `fewest`, uv will minimize the number of
-selected versions for each package, preferring older versions that are compatible with a
-wider range of supported Python versions or platforms.
+Under `fewest`, uv will minimize the number of selected versions for each package,
+preferring older versions that are compatible with a wider range of supported Python
+versions or platforms.
 
 **Default value**: `"fewest"`
 
@@ -2154,9 +2154,9 @@ By default, uv will optimize for selecting the latest version of each package fo
 supported Python version (`requires-python`), while minimizing the number of selected
 versions across platforms.
 
-Under `fewest`, uv will minimize the number of
-selected versions for each package, preferring older versions that are compatible with a
-wider range of supported Python versions or platforms.
+Under `fewest`, uv will minimize the number of selected versions for each package,
+preferring older versions that are compatible with a wider range of supported Python
+versions or platforms.
 
 **Default value**: `"fewest"`