Add a fast-path to skip resolution when installation is complete (#613)

For a very large resolution (a few hundred packages), I see 13ms vs.
400ms for a no-op. It's worth optimizing this case, in my opinion.

crates/distribution-types/src/installed.rs

@@ -1,11 +1,12 @@
 use std::path::{Path, PathBuf};
 use std::str::FromStr;
 
-use anyhow::{anyhow, Result};
+use anyhow::{anyhow, Context, Result};
+use fs_err as fs;
 
 use pep440_rs::Version;
 use puffin_normalize::PackageName;
-use pypi_types::DirectUrl;
+use pypi_types::{DirectUrl, Metadata21};
 
 use crate::{Metadata, VersionOrUrl};
 
@@ -114,6 +115,7 @@ impl InstalledDist {
         }
     }
 
+    /// Return the [`Version`] of the distribution.
     pub fn version(&self) -> &Version {
         match self {
             Self::Registry(dist) => &dist.version,
@@ -130,4 +132,12 @@ impl InstalledDist {
         let direct_url = serde_json::from_reader::<fs_err::File, DirectUrl>(file)?;
         Ok(Some(direct_url))
     }
+
+    /// Read the `METADATA` file from a `.dist-info` directory.
+    pub fn metadata(&self) -> Result<Metadata21> {
+        let path = self.path().join("METADATA");
+        let contents = fs::read(&path)?;
+        Metadata21::parse(&contents)
+            .with_context(|| format!("Failed to parse METADATA file at: {}", path.display()))
+    }
 }

crates/puffin-cli/src/commands/pip_install.rs

@@ -42,7 +42,7 @@ pub(crate) async fn pip_install(
     no_build: bool,
     exclude_newer: Option<DateTime<Utc>>,
     cache: Cache,
-    printer: Printer,
+    mut printer: Printer,
 ) -> Result<ExitStatus> {
     miette::set_hook(Box::new(|_| {
         Box::new(
@@ -54,6 +54,8 @@ pub(crate) async fn pip_install(
         )
     }))?;
 
+    let start = std::time::Instant::now();
+
     // Determine the requirements.
     let spec = specification(requirements, constraints, extras)?;
 
@@ -65,6 +67,23 @@ pub(crate) async fn pip_install(
         venv.python_executable().display()
     );
 
+    // If the requirements are already satisfied, we're done. Ideally, the resolver would be fast
+    // enough to let us remove this check. But right now, for large environments, it's an order of
+    // magnitude faster to validate the environment than to resolve the requirements.
+    if reinstall.is_none() && satisfied(&spec, &venv)? {
+        writeln!(
+            printer,
+            "{}",
+            format!(
+                "Audited {} in {}",
+                format!("{} package{}", spec.requirements.len(), "s").bold(),
+                elapsed(start.elapsed())
+            )
+            .dimmed()
+        )?;
+        return Ok(ExitStatus::Success);
+    }
+
     // Resolve the requirements.
     let resolution = resolve(
         spec,
@@ -140,6 +159,11 @@ fn specification(
     Ok(spec)
 }
 
+/// Returns `true` if the requirements are already satisfied.
+fn satisfied(spec: &RequirementsSpecification, venv: &Virtualenv) -> Result<bool> {
+    SitePackages::try_from_executable(venv)?.satisfies(&spec.requirements, &spec.constraints)
+}
+
 /// Resolve a set of requirements, similar to running `pip-compile`.
 #[allow(clippy::too_many_arguments)]
 async fn resolve(

crates/puffin-cli/tests/pip_install.rs

@@ -161,8 +161,7 @@ fn install_requirements_txt() -> Result<()> {
         ----- stdout -----
 
         ----- stderr -----
-        Resolved 2 packages in [TIME]
-        Audited 2 packages in [TIME]
+        Audited 1 packages in [TIME]
         "###);
     });
 
@@ -239,8 +238,7 @@ fn respect_installed() -> Result<()> {
         ----- stdout -----
 
         ----- stderr -----
-        Resolved 7 packages in [TIME]
-        Audited 7 packages in [TIME]
+        Audited 1 packages in [TIME]
         "###);
     });
 

crates/puffin-installer/src/plan.rs

@@ -307,4 +307,9 @@ impl Reinstall {
             Self::None
         }
     }
+
+    /// Returns `true` if no packages should be reinstalled.
+    pub fn is_none(&self) -> bool {
+        matches!(self, Self::None)
+    }
 }

crates/puffin-installer/src/site_packages.rs

@@ -1,14 +1,15 @@
 use std::collections::BTreeMap;
+use std::hash::BuildHasherDefault;
 
 use anyhow::{Context, Result};
 use fs_err as fs;
+use rustc_hash::FxHashSet;
 
 use distribution_types::{InstalledDist, Metadata, VersionOrUrl};
 use pep440_rs::Version;
 use pep508_rs::Requirement;
 use puffin_interpreter::Virtualenv;
 use puffin_normalize::PackageName;
-use pypi_types::Metadata21;
 
 #[derive(Debug)]
 pub struct SitePackages<'a> {
@@ -92,10 +93,7 @@ impl<'a> SitePackages<'a> {
 
         for (package, distribution) in &self.index {
             // Determine the dependencies for the given package.
-            let path = distribution.path().join("METADATA");
-            let contents = fs::read(&path)?;
-            let metadata = Metadata21::parse(&contents)
-                .with_context(|| format!("Failed to parse METADATA file at: {}", path.display()))?;
+            let metadata = distribution.metadata()?;
 
             // Verify that the dependencies are installed.
             for requirement in &metadata.requires_dist {
@@ -130,6 +128,63 @@ impl<'a> SitePackages<'a> {
 
         Ok(diagnostics)
     }
+
+    /// Returns `true` if the installed packages satisfy the given requirements.
+    pub fn satisfies(
+        &self,
+        requirements: &[Requirement],
+        constraints: &[Requirement],
+    ) -> Result<bool> {
+        let mut requirements = requirements.to_vec();
+        let mut seen =
+            FxHashSet::with_capacity_and_hasher(requirements.len(), BuildHasherDefault::default());
+
+        while let Some(requirement) = requirements.pop() {
+            if !requirement.evaluate_markers(self.venv.interpreter().markers(), &[]) {
+                continue;
+            }
+
+            let Some(distribution) = self.index.get(&requirement.name) else {
+                // The package isn't installed.
+                return Ok(false);
+            };
+
+            // Validate that the installed version matches the requirement.
+            match &requirement.version_or_url {
+                None | Some(pep508_rs::VersionOrUrl::Url(_)) => {}
+                Some(pep508_rs::VersionOrUrl::VersionSpecifier(version_specifier)) => {
+                    // The installed version doesn't satisfy the requirement.
+                    if !version_specifier.contains(distribution.version()) {
+                        return Ok(false);
+                    }
+                }
+            }
+
+            // Validate that the installed version satisfies the constraints.
+            for constraint in constraints {
+                if !constraint.evaluate_markers(self.venv.interpreter().markers(), &[]) {
+                    continue;
+                }
+
+                match &constraint.version_or_url {
+                    None | Some(pep508_rs::VersionOrUrl::Url(_)) => {}
+                    Some(pep508_rs::VersionOrUrl::VersionSpecifier(version_specifier)) => {
+                        // The installed version doesn't satisfy the constraint.
+                        if !version_specifier.contains(distribution.version()) {
+                            return Ok(false);
+                        }
+                    }
+                }
+            }
+
+            // Recurse into the dependencies.
+            if seen.insert(requirement) {
+                requirements.extend(distribution.metadata()?.requires_dist);
+            }
+        }
+
+        Ok(true)
+    }
 }
 
 impl IntoIterator for SitePackages<'_> {