Use the world SDK for cargo builds and seed it only when missing

cli/src/cargo.rs

@@ -3,7 +3,6 @@ use crate::{Host, world::World};
 use anyhow::{Context, Result, bail};
 use include_dir::{Dir, include_dir};
 use serde_json::{Value, json};
-use sha2::{Digest, Sha256};
 use std::time::Duration;
 use std::{
     path::{Path, PathBuf},
@@ -169,10 +168,9 @@ pub struct Cargo {
     runner: PathBuf,
     target: PathBuf,
     sdk: PathBuf,
-    sdk_files: Arc<std::collections::BTreeMap<PathBuf, Vec<u8>>>,
 }
 impl Cargo {
-    /// Installs changed SDK files and selects the current sausage executable as runner.
+    /// Seeds a missing world SDK and selects the current sausage executable as runner.
     pub fn new(world: World, cache: &Path) -> Result<Self> {
         let mut runner = std::env::current_exe()?;
         if runner
@@ -183,9 +181,23 @@ impl Cargo {
         }
         Self::with_runner(world, runner, cache)
     }
-    /// Installs the SDK and accepts an explicit sausage binary, including for init integrations.
+    /// Seeds a missing world SDK and accepts an explicit sausage binary, including for init integrations.
     pub fn with_runner(world: World, runner: PathBuf, cache: &Path) -> Result<Self> {
         let sdk = world.plugin_dir(ID).join("sdk");
+        Self::seed_sdk(&sdk)?;
+        Ok(Self {
+            sdk,
+            target: std::path::absolute(cache)?.join("cargo-target"),
+            world,
+            runner,
+            builds: Arc::new(tokio::sync::Mutex::new(())),
+        })
+    }
+    /// Seeds only an absent SDK; an existing world owns all of its SDK files.
+    fn seed_sdk(sdk: &Path) -> Result<()> {
+        if sdk.try_exists()? {
+            return Ok(());
+        }
         let mut files = std::collections::BTreeMap::new();
         collect_files(&SDK, Path::new("src"), &mut files);
         collect_files(&MACROS, Path::new("macros/src"), &mut files);
@@ -223,26 +235,23 @@ impl Cargo {
             }
             files.insert(destination, document.to_string().into_bytes());
         }
-        let mut hash = Sha256::new();
+        let parent = sdk.parent().context("SDK has no parent")?;
+        std::fs::create_dir_all(parent).with_context(|| format!("create {}", parent.display()))?;
+        let staging = tempfile::Builder::new()
+            .prefix("seed-sdk-")
+            .tempdir_in(parent)
+            .with_context(|| format!("stage SDK in {}", parent.display()))?;
         for (path, bytes) in &files {
-            let name = path.to_str().unwrap().as_bytes();
-            hash.update((name.len() as u64).to_le_bytes());
-            hash.update(name);
-            hash.update((bytes.len() as u64).to_le_bytes());
-            hash.update(bytes);
-            write_changed(&sdk.join(path), bytes)?;
+            write_changed(&staging.path().join(path), bytes)?;
         }
-        let cached = std::path::absolute(cache)?
-            .join("sdk")
-            .join(format!("{:x}", hash.finalize()));
-        Ok(Self {
-            sdk: cached,
-            sdk_files: Arc::new(files),
-            target: std::path::absolute(cache)?.join("cargo-target"),
-            world,
-            runner,
-            builds: Arc::new(tokio::sync::Mutex::new(())),
-        })
+        // Another builder may have seeded the world while we prepared the files.
+        if !sdk.try_exists()?
+            && let Err(error) = std::fs::rename(staging.path(), sdk)
+            && !sdk.try_exists()?
+        {
+            return Err(error).with_context(|| format!("seed {}", sdk.display()));
+        }
+        Ok(())
     }
     /// Registers cargo.build as a cancellable native process.
     pub fn register(self, host: &Host) {
@@ -310,27 +319,8 @@ impl Cargo {
         let source = source.to_path_buf();
         let copy = work.clone();
         let sdk = self.sdk.clone();
-        let sdk_files = self.sdk_files.clone();
         let build_guard = tokio::task::spawn_blocking(move || -> Result<_> {
-            // Host startup installs only the readable world copy. Builds populate the cache.
-            if !sdk.is_dir() {
-                let parent = sdk.parent().unwrap();
-                std::fs::create_dir_all(parent)
-                    .with_context(|| format!("create {}", parent.display()))?;
-                let staging = tempfile::Builder::new()
-                    .prefix("install-")
-                    .tempdir_in(parent)
-                    .with_context(|| format!("stage SDK in {}", parent.display()))?;
-                for (path, bytes) in sdk_files.iter() {
-                    write_changed(&staging.path().join(path), bytes)?;
-                }
-                // Another builder can publish the same complete SDK first.
-                if let Err(error) = std::fs::rename(staging.path(), &sdk)
-                    && !sdk.is_dir()
-                {
-                    return Err(error).with_context(|| format!("install {}", sdk.display()));
-                }
-            }
+            Self::seed_sdk(&sdk)?;
             if cleanup.exists() {
                 std::fs::remove_dir_all(&cleanup)
                     .with_context(|| format!("remove {}", cleanup.display()))?;
@@ -659,7 +649,7 @@ fn write_changed(path: &Path, bytes: &[u8]) -> Result<()> {
     }
     Ok(())
 }
-/// Collects embedded source files for deterministic hashing and installation.
+/// Collects embedded source files for seeding a missing world SDK.
 fn collect_files(
     directory: &Dir<'_>,
     destination: &Path,