3 files changed, 96 insertions, 4 deletions

diff --git a/cli/npm/registry.rs b/cli/npm/registry.rs
index c70741b01..1fb4b2e0a 100644
--- a/cli/npm/registry.rs
+++ b/cli/npm/registry.rs
@@ -31,6 +31,8 @@ use super::semver::NpmVersionReq;
 pub struct NpmPackageInfo {
   pub name: String,
   pub versions: HashMap<String, NpmPackageVersionInfo>,
+  #[serde(rename = "dist-tags")]
+  pub dist_tags: HashMap<String, String>,
 }
 
 pub struct NpmDependencyEntry {
@@ -39,7 +41,7 @@ pub struct NpmDependencyEntry {
   pub version_req: NpmVersionReq,
 }
 
-#[derive(Debug, Deserialize, Serialize, Clone)]
+#[derive(Debug, Default, Deserialize, Serialize, Clone)]
 pub struct NpmPackageVersionInfo {
   pub version: String,
   pub dist: NpmPackageVersionDistInfo,
@@ -89,7 +91,7 @@ impl NpmPackageVersionInfo {
   }
 }
 
-#[derive(Debug, Deserialize, Serialize, Clone)]
+#[derive(Debug, Default, Deserialize, Serialize, Clone)]
 pub struct NpmPackageVersionDistInfo {
   /// URL to the tarball.
   pub tarball: String,
@@ -231,7 +233,20 @@ impl NpmRegistryApi {
       Err(err) if err.kind() == ErrorKind::NotFound => return Ok(None),
       Err(err) => return Err(err.into()),
     };
-    Ok(serde_json::from_str(&file_text)?)
+    match serde_json::from_str(&file_text) {
+      Ok(package_info) => Ok(Some(package_info)),
+      Err(err) => {
+        // This scenario might mean we need to load more data from the
+        // npm registry than before. So, just debug log while in debug
+        // rather than panic.
+        log::debug!(
+          "error deserializing registry.json for '{}'. Reloading. {:?}",
+          name,
+          err
+        );
+        Ok(None)
+      }
+    }
   }
 
   fn save_package_info_to_file_cache(
diff --git a/cli/npm/resolution.rs b/cli/npm/resolution.rs
index 4f46bbed4..8fac92716 100644
--- a/cli/npm/resolution.rs
+++ b/cli/npm/resolution.rs
@@ -19,9 +19,10 @@ use super::semver::NpmVersion;
 use super::semver::SpecifierVersionReq;
 
 /// The version matcher used for npm schemed urls is more strict than
-/// the one used by npm packages.
+/// the one used by npm packages and so we represent either via a trait.
 pub trait NpmVersionMatcher {
   fn matches(&self, version: &NpmVersion) -> bool;
+  fn is_latest(&self) -> bool;
   fn version_text(&self) -> String;
 }
 
@@ -112,6 +113,10 @@ impl NpmVersionMatcher for NpmPackageReq {
     }
   }
 
+  fn is_latest(&self) -> bool {
+    self.version_req.is_none()
+  }
+
   fn version_text(&self) -> String {
     self
       .version_req
@@ -484,6 +489,25 @@ fn get_resolved_package_version_and_info(
   parent: Option<&NpmPackageId>,
 ) -> Result<VersionAndInfo, AnyError> {
   let mut maybe_best_version: Option<VersionAndInfo> = None;
+  if version_matcher.is_latest() {
+    if let Some(version) = info.dist_tags.get("latest") {
+      match info.versions.get(version) {
+        Some(info) => {
+          return Ok(VersionAndInfo {
+            version: NpmVersion::parse(version)?,
+            info: info.clone(),
+          });
+        }
+        None => {
+          bail!(
+            "Could not find version '{}' referenced in dist-tag 'latest'.",
+            version,
+          )
+        }
+      }
+    }
+  }
+
   for (_, version_info) in info.versions.into_iter() {
     let version = NpmVersion::parse(&version_info.version)?;
     if version_matcher.matches(&version) {
@@ -651,4 +675,53 @@ mod tests {
     assert_eq!(name_without_path("@foo/bar/baz"), "@foo/bar");
     assert_eq!(name_without_path("@hello"), "@hello");
   }
+
+  #[test]
+  fn test_get_resolved_package_version_and_info() {
+    // dist tag where version doesn't exist
+    let package_ref = NpmPackageReference::from_str("npm:test").unwrap();
+    let result = get_resolved_package_version_and_info(
+      "test",
+      &package_ref.req,
+      NpmPackageInfo {
+        name: "test".to_string(),
+        versions: HashMap::new(),
+        dist_tags: HashMap::from([(
+          "latest".to_string(),
+          "1.0.0-alpha".to_string(),
+        )]),
+      },
+      None,
+    );
+    assert_eq!(
+      result.err().unwrap().to_string(),
+      "Could not find version '1.0.0-alpha' referenced in dist-tag 'latest'."
+    );
+
+    // dist tag where version is a pre-release
+    let package_ref = NpmPackageReference::from_str("npm:test").unwrap();
+    let result = get_resolved_package_version_and_info(
+      "test",
+      &package_ref.req,
+      NpmPackageInfo {
+        name: "test".to_string(),
+        versions: HashMap::from([
+          ("0.1.0".to_string(), NpmPackageVersionInfo::default()),
+          (
+            "1.0.0-alpha".to_string(),
+            NpmPackageVersionInfo {
+              version: "0.1.0-alpha".to_string(),
+              ..Default::default()
+            },
+          ),
+        ]),
+        dist_tags: HashMap::from([(
+          "latest".to_string(),
+          "1.0.0-alpha".to_string(),
+        )]),
+      },
+      None,
+    );
+    assert_eq!(result.unwrap().version.to_string(), "1.0.0-alpha");
+  }
 }
diff --git a/cli/npm/semver/mod.rs b/cli/npm/semver/mod.rs
index 10a87a13f..53f0f199f 100644
--- a/cli/npm/semver/mod.rs
+++ b/cli/npm/semver/mod.rs
@@ -174,6 +174,10 @@ impl NpmVersionMatcher for NpmVersionReq {
     self.satisfies(version)
   }
 
+  fn is_latest(&self) -> bool {
+    false
+  }
+
   fn version_text(&self) -> String {
     self.raw_text.clone()
   }