refactor: separate out node warning check

Separate out the node version warning rule to its own function and add
tests to cover the cases.

packages/hardhat-core/src/internal/cli/bootstrap.ts

@@ -1,10 +1,10 @@
 #!/usr/bin/env node
-import semver from "semver";
+
 import chalk from "chalk";
 
-import { SUPPORTED_NODE_VERSIONS } from "./constants";
+import { isNodeVersionToWarnOn } from "./is-node-version-to-warn-on";
 
-if (!semver.satisfies(process.version, SUPPORTED_NODE_VERSIONS.join(" || "))) {
+if (isNodeVersionToWarnOn(process.version)) {
   console.warn(
     chalk.yellow.bold(`WARNING:`),
     `You are currently using Node.js ${process.version}, which is not supported by Hardhat. This can lead to unexpected behavior. See https://hardhat.org/nodejs-versions`

packages/hardhat-core/src/internal/cli/is-node-version-to-warn-on.ts

@@ -0,0 +1,16 @@
+import semver from "semver";
+
+import { SUPPORTED_NODE_VERSIONS } from "./constants";
+
+/**
+ * Determine if the node version is unsupported by Hardhat
+ * and so a warning message should be shown.
+ *
+ * The current rule is that Hardhat supports all `Current`,
+ * `Active LTS`, and `Maintenance LTS` versions of Node.js
+ * as defined in the Node.js release schedule and encoded
+ * in the `SUPPORTED_NODE_VERSIONS` constant.
+ */
+export function isNodeVersionToWarnOn(nodeVersion: string): boolean {
+  return !semver.satisfies(nodeVersion, SUPPORTED_NODE_VERSIONS.join(" || "));
+}

packages/hardhat-core/test/internal/cli/is-node-version-to-warn-on.ts

@@ -0,0 +1,43 @@
+import { assert } from "chai";
+import { isNodeVersionToWarnOn } from "../../../src/internal/cli/is-node-version-to-warn-on";
+
+describe("isNodeVersionToWarnOn", function () {
+  it("Should not warn on supported versions", function () {
+    assert.isFalse(isNodeVersionToWarnOn("v18.0.0"));
+    assert.isFalse(isNodeVersionToWarnOn("v18.20.3"));
+
+    assert.isFalse(isNodeVersionToWarnOn("v20.0.0"));
+    assert.isFalse(isNodeVersionToWarnOn("v20.14.0"));
+
+    assert.isFalse(isNodeVersionToWarnOn("v22.0.0"));
+    assert.isFalse(isNodeVersionToWarnOn("v22.3.0"));
+  });
+
+  it("Should warn on unsupported older node versions", function () {
+    assert(isNodeVersionToWarnOn("v10.0.0"));
+    assert(isNodeVersionToWarnOn("v10.24.1"));
+
+    assert(isNodeVersionToWarnOn("v12.0.0"));
+    assert(isNodeVersionToWarnOn("v12.22.12"));
+
+    assert(isNodeVersionToWarnOn("v14.0.0"));
+    assert(isNodeVersionToWarnOn("v14.21.3"));
+
+    assert(isNodeVersionToWarnOn("v16.0.0"));
+    assert(isNodeVersionToWarnOn("v16.20.20"));
+  });
+
+  it("Should warn on unsupported newer versions", function () {
+    assert(isNodeVersionToWarnOn("v24.0.0"));
+    assert(isNodeVersionToWarnOn("v24.3.0"));
+  });
+
+  it("Should warn on unsupported odd number releases", function () {
+    assert(isNodeVersionToWarnOn("v15.14.0"));
+    assert(isNodeVersionToWarnOn("v17.9.1"));
+    assert(isNodeVersionToWarnOn("v19.9.0"));
+    assert(isNodeVersionToWarnOn("v21.7.3"));
+    assert(isNodeVersionToWarnOn("v23.0.0"));
+    assert(isNodeVersionToWarnOn("v25.0.0"));
+  });
+});