Adds support for --no-deps to pip compile (#1311)

Mostly throwing this up here as a discussion topic. Having something
like this is primarily useful for enabling use cases similar to `rye
add` where I want to use this currently. One can accomplish something
similar with `unearth` today or by abusing regular `pip install`:

```
$ ~/.rye/self/bin/pip install --no-deps --dry-run flask --report - -q | jq '.install[0].metadata | {name, version}'
{
  "name": "Flask",
  "version": "3.0.2"
}
```

Another option would be to have a `puffin resolve` command or similar
that works like `pip compile` without dependencies, takes the
requirements as arguments and returns a line for each resolution. That
would be a larger change.

crates/puffin/src/commands/pip_compile.rs

@@ -27,8 +27,8 @@ use puffin_installer::{Downloader, NoBinary};
 use puffin_interpreter::{Interpreter, PythonVersion};
 use puffin_normalize::{ExtraName, PackageName};
 use puffin_resolver::{
-    DisplayResolutionGraph, InMemoryIndex, Manifest, OptionsBuilder, PreReleaseMode,
-    ResolutionMode, Resolver,
+    DependencyMode, DisplayResolutionGraph, InMemoryIndex, Manifest, OptionsBuilder,
+    PreReleaseMode, ResolutionMode, Resolver,
 };
 use puffin_traits::{InFlight, NoBuild, SetupPyStrategy};
 use puffin_warnings::warn_user;
@@ -51,6 +51,7 @@ pub(crate) async fn pip_compile(
     output_file: Option<&Path>,
     resolution_mode: ResolutionMode,
     prerelease_mode: PreReleaseMode,
+    dependency_mode: DependencyMode,
     upgrade: Upgrade,
     generate_hashes: bool,
     include_annotations: bool,
@@ -212,6 +213,7 @@ pub(crate) async fn pip_compile(
     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

@@ -191,6 +191,11 @@ struct PipCompileArgs {
     #[clap(long, conflicts_with = "extra")]
     all_extras: bool,
 
+    /// Ignore package dependencies, instead only add those packages explicitly listed
+    /// on the command line to the resulting the requirements file.
+    #[clap(long)]
+    no_deps: bool,
+
     #[clap(long, value_enum, default_value_t = ResolutionMode::default())]
     resolution: ResolutionMode,
 
@@ -807,6 +812,11 @@ async fn run() -> Result<ExitStatus> {
             };
             let upgrade = Upgrade::from_args(args.upgrade, args.upgrade_package);
             let no_build = NoBuild::from_args(args.only_binary, args.no_build);
+            let dependency_mode = if args.no_deps {
+                DependencyMode::Direct
+            } else {
+                DependencyMode::Transitive
+            };
             commands::pip_compile(
                 &requirements,
                 &constraints,
@@ -815,6 +825,7 @@ async fn run() -> Result<ExitStatus> {
                 args.output_file.as_deref(),
                 args.resolution,
                 args.prerelease,
+                dependency_mode,
                 upgrade,
                 args.generate_hashes,
                 !args.no_annotate,

crates/puffin/tests/pip_compile.rs

@@ -480,6 +480,33 @@ fn compile_python_312() -> Result<()> {
     Ok(())
 }
 
+/// Resolve a specific version of Black at Python 3.12 without deps.
+#[test]
+fn compile_python_312_no_deps() -> Result<()> {
+    let context = TestContext::new("3.12");
+    let requirements_in = context.temp_dir.child("requirements.in");
+    requirements_in.write_str("black==23.10.1")?;
+
+    puffin_snapshot!(context.compile()
+            .arg("requirements.in")
+            .arg("--no-deps")
+            .arg("--python-version")
+            .arg("3.12"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    # This file was autogenerated by Puffin v[VERSION] via the following command:
+    #    puffin pip compile --cache-dir [CACHE_DIR] --exclude-newer 2023-11-18T12:00:00Z requirements.in --no-deps --python-version 3.12
+    black==23.10.1
+
+    ----- stderr -----
+    Resolved 1 package in [TIME]
+    "###
+    );
+
+    Ok(())
+}
+
 /// Resolve a specific version of Black at Python 3.7.
 #[test]
 fn compile_python_37() -> Result<()> {