feat: add "lts" version option (#97)

(cherry picked from commit a1496dd8d9)

src/version.ts

@@ -9,12 +9,12 @@ const GIT_HASH_RE = /^[0-9a-fA-F]{40}$/;
 
 export interface VersionRange {
   range: string;
-  kind: "canary" | "rc" | "stable";
+  kind: "canary" | "rc" | "stable" | "lts";
 }
 
 export interface Version {
   version: string;
-  kind: "canary" | "rc" | "stable";
+  kind: "canary" | "rc" | "stable" | "lts";
 }
 
 /** Parses the version from the user into a structure */
@@ -36,6 +36,10 @@ export function parseVersionRange(
     return { range: "latest", kind: "stable" };
   }
 
+  if (version === "lts") {
+    return { range: "latest", kind: "lts" };
+  }
+
   if (GIT_HASH_RE.test(version)) {
     return { range: version, kind: "canary" };
   }
@@ -82,6 +86,8 @@ export function resolveVersion(
   } else if (kind === "rc") {
     // range is always "latest"
     return resolveReleaseCandidate();
+  } else if (kind === "lts") {
+    return resolveLTS();
   } else {
     return resolveRelease(range);
   }
@@ -120,6 +126,22 @@ async function resolveReleaseCandidate(): Promise<Version | null> {
   return { version, kind: "rc" };
 }
 
+async function resolveLTS(): Promise<Version | null> {
+  const res = await fetchWithRetries(
+    "https://dl.deno.land/release-lts-latest.txt",
+  );
+  if (res.status !== 200) {
+    throw new Error(
+      "Failed to fetch LTS version info from dl.deno.land. Please try again later.",
+    );
+  }
+  const version = semver.clean((await res.text()).trim());
+  if (version === null) {
+    throw new Error("Failed to parse LTS version.");
+  }
+  return { version, kind: "lts" };
+}
+
 async function resolveRelease(range: string): Promise<Version | null> {
   if (range === "latest") {
     const res = await fetchWithRetries(