fix: answer without an import graph where TypeScript is the native 7

.changeset/import-graph-typescript-7.md

@@ -0,0 +1,5 @@
+---
+"diagnostics-webpack-plugin": patch
+---
+
+Lint every file again, rather than fail, where a project's TypeScript is the native TypeScript 7, which has no API to read what a file imports through: a check reading across files failed with `Cannot read properties of undefined (reading 'readFile')`.

README.md

@@ -381,7 +381,8 @@ drops it before webpack sees it — and this holds for every check, whatever too
 it runs. A change that could reach files some other way — a declaration file
 nothing imports, a `declare global`, a config file, an import that resolves to
 nothing (a stylesheet, an image or another asset webpack bundles aside) — lints
-every file again, as does a project without TypeScript. There,
+every file again, as does a project without TypeScript, or with TypeScript 7,
+whose native compiler has no API to read imports through. There,
 an ESLint check with `cache: true` written down keeps ESLint's own cache, which
 answers for a file whose import changed from before the change.
 

src/import-graph.js

@@ -386,7 +386,19 @@ function getGraph(compiler, context, owner) {
           ).href
         );
 
-        return createGraph(loaded.default || loaded);
+        const ts = loaded.default || loaded;
+
+        // TypeScript 7 is a native compiler whose package exports no such
+        // API: what a file imports cannot be read through it.
+        if (
+          typeof ts.preProcessFile !== "function" ||
+          typeof ts.resolveModuleName !== "function" ||
+          !ts.sys
+        ) {
+          return undefined;
+        }
+
+        return createGraph(ts);
       } catch {
         // Without a TypeScript of the project's own there is nothing to say
         // which file reads which, and every file is linted again instead.

test/import-graph.test.js

@@ -369,6 +369,22 @@ describe("the graph a compiler keeps", () => {
 
     assert.strictEqual(await getGraph({}, project), undefined);
   });
+
+  it("should be nothing for a project whose TypeScript has no API to read imports with", async (t) => {
+    // As TypeScript 7 is: a native compiler whose package exports a version.
+    const project = mkdtempSync(join(tmpdir(), "native-typescript-"));
+    const native = join(project, "node_modules", "typescript");
+
+    t.after(() => rmSync(project, { recursive: true, force: true }));
+    mkdirSync(native, { recursive: true });
+    writeFileSync(join(native, "package.json"), '{ "main": "index.js" }');
+    writeFileSync(
+      join(native, "index.js"),
+      'module.exports = { version: "7.0.0", versionMajorMinor: "7.0" };\n',
+    );
+
+    assert.strictEqual(await getGraph({}, project), undefined);
+  });
 });
 
 describe("signatures", () => {