Allow user to constrain supported lock environments (#6210)

## Summary

The strategy here is: if the user provides supported environments, we
use those as the initial forks when resolving. As a result, we never add
or explore branches that are disjoint with the supported environments.
(If the supported environments change, we ignore the lockfile entirely,
so we don't have to worry about any interactions between supported
environments and the preference forks.)

Closes https://github.com/astral-sh/uv/issues/6184.

crates/uv-workspace/src/pyproject.rs

@@ -14,6 +14,7 @@ use serde::{Deserialize, Serialize};
 use thiserror::Error;
 use url::Url;
 
+use crate::environments::SupportedEnvironments;
 use pep440_rs::VersionSpecifiers;
 use pypi_types::{RequirementSource, VerbatimParsedUrl};
 use uv_git::GitReference;
@@ -98,6 +99,8 @@ pub struct ToolUv {
         "#
     )]
     pub managed: Option<bool>,
+    /// The project's development dependencies. Development dependencies will be installed by
+    /// default in `uv run` and `uv sync`, but will not appear in the project's published metadata.
     #[cfg_attr(
         feature = "schemars",
         schemars(
@@ -105,12 +108,40 @@ pub struct ToolUv {
             description = "PEP 508-style requirements, e.g., `ruff==0.5.0`, or `ruff @ https://...`."
         )
     )]
+    #[option(
+        default = r#"[]"#,
+        value_type = "list[str]",
+        example = r#"
+            dev_dependencies = ["ruff==0.5.0"]
+        "#
+    )]
     pub dev_dependencies: Option<Vec<pep508_rs::Requirement<VerbatimParsedUrl>>>,
+    /// A list of supported environments against which to resolve dependencies.
+    ///
+    /// By default, uv will resolve for all possible environments during a `uv lock` operation.
+    /// However, you can restrict the set of supported environments to improve performance and avoid
+    /// unsatisfiable branches in the solution space.
     #[cfg_attr(
         feature = "schemars",
         schemars(
             with = "Option<Vec<String>>",
-            description = "PEP 508 style requirements, e.g. `ruff==0.5.0`, or `ruff @ https://...`."
+            description = "A list of environment markers, e.g. `python_version >= '3.6'`."
+        )
+    )]
+    #[option(
+        default = r#"[]"#,
+        value_type = "str | list[str]",
+        example = r#"
+            # Resolve for macOS, but not for Linux or Windows.
+            environments = ["sys_platform == 'darwin'"]
+        "#
+    )]
+    pub environments: Option<SupportedEnvironments>,
+    #[cfg_attr(
+        feature = "schemars",
+        schemars(
+            with = "Option<Vec<String>>",
+            description = "PEP 508-style requirements, e.g. `ruff==0.5.0`, or `ruff @ https://...`."
         )
     )]
     pub override_dependencies: Option<Vec<pep508_rs::Requirement<VerbatimParsedUrl>>>,