feat: catch preprocess errors

lib/linter/linter.js

@@ -1510,7 +1510,33 @@ class Linter {
             options.filterCodeBlock ||
             (blockFilename => blockFilename.endsWith(".js"));
         const originalExtname = path.extname(filename);
-        const messageLists = preprocess(text, filenameToExpose).map((block, i) => {
+        let blocks;
+
+        try {
+            blocks = preprocess(text, filenameToExpose);
+        } catch (ex) {
+
+            // If the message includes a leading line number, strip it:
+            const message = `Preprocessing error: ${ex.message.replace(/^line \d+:/iu, "").trim()}`;
+
+            debug("%s\n%s", message, ex.stack);
+
+            return [
+                {
+                    success: false,
+                    error: {
+                        ruleId: null,
+                        fatal: true,
+                        severity: 2,
+                        message,
+                        line: ex.lineNumber,
+                        column: ex.column
+                    }
+                }
+            ];
+        }
+
+        const messageLists = blocks.map((block, i) => {
             debug("A code block was found: %o", block.filename || "(unnamed)");
 
             // Keep the legacy behavior.

tests/lib/linter/linter.js

@@ -6660,6 +6660,23 @@ var a = "test2";
                 assert.strictEqual(preprocess.calledOnce, true);
                 assert.deepStrictEqual(preprocess.args[0], [code, filename]);
             });
+
+            it("should catch preprocess error.", () => {
+                const code = "foo";
+                const preprocess = sinon.spy(() => {
+                    throw Object.assign(new SyntaxError("Invalid syntax"), {
+                        lineNumber: 1,
+                        column: 1
+                    });
+                });
+
+                linter.verify(code, {});
+                const sourceCode = linter.getSourceCode();
+
+                assert.throw(() => linter.verify(sourceCode, {}, { filename, preprocess }), "Invalid syntax");
+                assert.strictEqual(preprocess.calledOnce, true);
+                assert.deepStrictEqual(preprocess.args[0], [code, filename]);
+            });
         });
 
         describe("postprocessors", () => {