Add support for `--no-deps` to `pip install` (#1191)

## Summary

Closes https://github.com/astral-sh/puffin/issues/1188.

crates/puffin-resolver/src/dependency_mode.rs

@@ -0,0 +1,20 @@
+#[derive(Debug, Default, Clone, Copy)]
+pub enum DependencyMode {
+    /// Include all dependencies, whether direct or transitive.
+    #[default]
+    Transitive,
+    /// Exclude transitive dependencies, only resolving the root package's immediate dependencies.
+    Direct,
+}
+
+impl DependencyMode {
+    /// Returns `true` if transitive dependencies should be included.
+    pub fn is_transitive(self) -> bool {
+        matches!(self, Self::Transitive)
+    }
+
+    /// Returns `true` if (only) direct dependencies should be excluded.
+    pub fn is_direct(self) -> bool {
+        matches!(self, Self::Direct)
+    }
+}

crates/puffin-resolver/src/lib.rs

@@ -1,3 +1,4 @@
+pub use dependency_mode::DependencyMode;
 pub use error::ResolveError;
 pub use finder::{DistFinder, Reporter as FinderReporter};
 pub use manifest::Manifest;
@@ -10,6 +11,7 @@ pub use resolver::{
 };
 
 mod candidate_selector;
+mod dependency_mode;
 mod error;
 mod finder;
 mod manifest;

crates/puffin-resolver/src/options.rs

@@ -1,12 +1,13 @@
 use chrono::{DateTime, Utc};
 
-use crate::{PreReleaseMode, ResolutionMode};
+use crate::{DependencyMode, PreReleaseMode, ResolutionMode};
 
 /// Options for resolving a manifest.
 #[derive(Debug, Default, Copy, Clone)]
 pub struct Options {
     pub resolution_mode: ResolutionMode,
     pub prerelease_mode: PreReleaseMode,
+    pub dependency_mode: DependencyMode,
     pub exclude_newer: Option<DateTime<Utc>>,
 }
 
@@ -15,6 +16,7 @@ pub struct Options {
 pub struct OptionsBuilder {
     resolution_mode: ResolutionMode,
     prerelease_mode: PreReleaseMode,
+    dependency_mode: DependencyMode,
     exclude_newer: Option<DateTime<Utc>>,
 }
 
@@ -38,6 +40,13 @@ impl OptionsBuilder {
         self
     }
 
+    /// Sets the dependency mode.
+    #[must_use]
+    pub fn dependency_mode(mut self, dependency_mode: DependencyMode) -> Self {
+        self.dependency_mode = dependency_mode;
+        self
+    }
+
     /// Sets the exclusion date.
     #[must_use]
     pub fn exclude_newer(mut self, exclude_newer: Option<DateTime<Utc>>) -> Self {
@@ -50,6 +59,7 @@ impl OptionsBuilder {
         Options {
             resolution_mode: self.resolution_mode,
             prerelease_mode: self.prerelease_mode,
+            dependency_mode: self.dependency_mode,
             exclude_newer: self.exclude_newer,
         }
     }

crates/puffin-resolver/src/resolver/mod.rs

@@ -50,7 +50,7 @@ pub use crate::resolver::provider::ResolverProvider;
 use crate::resolver::reporter::Facade;
 pub use crate::resolver::reporter::{BuildId, Reporter};
 use crate::version_map::VersionMap;
-use crate::Options;
+use crate::{DependencyMode, Options};
 
 mod allowed_urls;
 mod index;
@@ -63,6 +63,7 @@ pub struct Resolver<'a, Provider: ResolverProvider> {
     constraints: Vec<Requirement>,
     overrides: Overrides,
     allowed_urls: AllowedUrls,
+    dependency_mode: DependencyMode,
     markers: &'a MarkerEnvironment,
     python_requirement: PythonRequirement,
     selector: CandidateSelector,
@@ -173,6 +174,7 @@ impl<'a, Provider: ResolverProvider> Resolver<'a, Provider> {
             visited: DashSet::default(),
             selector,
             allowed_urls,
+            dependency_mode: options.dependency_mode,
             project: manifest.project,
             requirements: manifest.requirements,
             constraints: manifest.constraints,
@@ -644,6 +646,11 @@ impl<'a, Provider: ResolverProvider> Resolver<'a, Provider> {
             }
 
             PubGrubPackage::Package(package_name, extra, url) => {
+                // If we're excluding transitive dependencies, short-circuit.
+                if self.dependency_mode.is_direct() {
+                    return Ok(Dependencies::Available(DependencyConstraints::default()));
+                }
+
                 // Wait for the metadata to be available.
                 let dist = match url {
                     Some(url) => PubGrubDistribution::from_url(package_name, url),

crates/puffin/src/commands/pip_install.rs

@@ -26,8 +26,8 @@ use puffin_installer::{
 use puffin_interpreter::{Interpreter, Virtualenv};
 use puffin_normalize::PackageName;
 use puffin_resolver::{
-    InMemoryIndex, Manifest, Options, OptionsBuilder, PreReleaseMode, ResolutionGraph,
-    ResolutionMode, Resolver,
+    DependencyMode, InMemoryIndex, Manifest, Options, OptionsBuilder, PreReleaseMode,
+    ResolutionGraph, ResolutionMode, Resolver,
 };
 use puffin_traits::{InFlight, SetupPyStrategy};
 use requirements_txt::EditableRequirement;
@@ -46,6 +46,7 @@ pub(crate) async fn pip_install(
     extras: &ExtrasSpecification<'_>,
     resolution_mode: ResolutionMode,
     prerelease_mode: PreReleaseMode,
+    dependency_mode: DependencyMode,
     index_locations: IndexLocations,
     reinstall: &Reinstall,
     link_mode: LinkMode,
@@ -154,6 +155,7 @@ pub(crate) async fn pip_install(
     let options = OptionsBuilder::new()
         .resolution_mode(resolution_mode)
         .prerelease_mode(prerelease_mode)
+        .dependency_mode(dependency_mode)
         .exclude_newer(exclude_newer)
         .build();
 

crates/puffin/src/main.rs

@@ -15,7 +15,7 @@ use puffin_cache::{Cache, CacheArgs, Refresh};
 use puffin_installer::{NoBinary, Reinstall};
 use puffin_interpreter::PythonVersion;
 use puffin_normalize::{ExtraName, PackageName};
-use puffin_resolver::{PreReleaseMode, ResolutionMode};
+use puffin_resolver::{DependencyMode, PreReleaseMode, ResolutionMode};
 use puffin_traits::SetupPyStrategy;
 use requirements::ExtrasSpecification;
 
@@ -445,6 +445,11 @@ struct PipInstallArgs {
     #[clap(long)]
     refresh_package: Vec<PackageName>,
 
+    /// Ignore package dependencies, instead only installing those packages explicitly listed
+    /// on the command line or in the requirements files.
+    #[clap(long)]
+    no_deps: bool,
+
     /// The method to use when installing packages from the global cache.
     #[clap(long, value_enum, default_value_t = install_wheel_rs::linker::LinkMode::default())]
     link_mode: install_wheel_rs::linker::LinkMode,
@@ -802,6 +807,11 @@ async fn run() -> Result<ExitStatus> {
             };
             let reinstall = Reinstall::from_args(args.reinstall, args.reinstall_package);
             let no_binary = NoBinary::from_args(args.no_binary, args.no_binary_package);
+            let dependency_mode = if args.no_deps {
+                DependencyMode::Direct
+            } else {
+                DependencyMode::Transitive
+            };
             commands::pip_install(
                 &requirements,
                 &constraints,
@@ -809,6 +819,7 @@ async fn run() -> Result<ExitStatus> {
                 &extras,
                 args.resolution,
                 args.prerelease,
+                dependency_mode,
                 index_urls,
                 &reinstall,
                 args.link_mode,

crates/puffin/tests/pip_install.rs

@@ -1099,3 +1099,48 @@ fn install_executable_hardlink() -> Result<()> {
 
     Ok(())
 }
+
+/// Install a package from the command line into a virtual environment, ignoring its dependencies.
+#[test]
+fn no_deps() -> Result<()> {
+    let temp_dir = assert_fs::TempDir::new()?;
+    let cache_dir = assert_fs::TempDir::new()?;
+    let venv = create_venv_py312(&temp_dir, &cache_dir);
+
+    // Install Flask.
+    insta::with_settings!({
+        filters => INSTA_FILTERS.to_vec()
+    }, {
+        assert_cmd_snapshot!(Command::new(get_cargo_bin(BIN_NAME))
+            .arg("pip")
+            .arg("install")
+            .arg("Flask")
+            .arg("--no-deps")
+            .arg("--strict")
+            .arg("--cache-dir")
+            .arg(cache_dir.path())
+            .arg("--exclude-newer")
+            .arg(EXCLUDE_NEWER)
+            .env("VIRTUAL_ENV", venv.as_os_str())
+            .current_dir(&temp_dir), @r###"
+        success: true
+        exit_code: 0
+        ----- stdout -----
+
+        ----- stderr -----
+        Resolved 1 package in [TIME]
+        Downloaded 1 package in [TIME]
+        Installed 1 package in [TIME]
+         + flask==3.0.0
+        warning: The package `flask` requires `werkzeug >=3.0.0`, but it's not installed.
+        warning: The package `flask` requires `jinja2 >=3.1.2`, but it's not installed.
+        warning: The package `flask` requires `itsdangerous >=2.1.2`, but it's not installed.
+        warning: The package `flask` requires `click >=8.1.3`, but it's not installed.
+        warning: The package `flask` requires `blinker >=1.6.2`, but it's not installed.
+        "###);
+    });
+
+    assert_command(&venv, "import flask", &temp_dir).failure();
+
+    Ok(())
+}