Report diagnostics with TypeScript Compiler API.

README.md

$ node --disable-warning=ExperimentalWarning test.mts
error TS0: Configuration not found.
path/to/test.css:1:2 - error TS0: CSS selector is not used.

1 .foo { color: red; }
   ~~~

report-diagnostics-with-typescript.mts

import ts from 'typescript';

const host: ts.FormatDiagnosticsHost = {
  getCurrentDirectory: () => '/app',
  getCanonicalFileName: (fileName) => (ts.sys.useCaseSensitiveFileNames ? fileName : fileName.toLowerCase()),
  getNewLine: () => ts.sys.newLine,
};

const file = ts.createSourceFile(
  '/app/path/to/test.css',
  '.foo { color: red; }',
  ts.ScriptTarget.ESNext,
  false,
  ts.ScriptKind.Unknown,
);

const diagnostic1: ts.Diagnostic = {
  category: ts.DiagnosticCategory.Error,
  code: 0,
  file: undefined,
  start: undefined,
  length: undefined,
  messageText: 'Configuration not found.',
};
const diagnostic2: ts.Diagnostic = {
  category: ts.DiagnosticCategory.Error,
  code: 0,
  file,
  start: 1,
  length: 3,
  messageText: 'CSS selector is not used.',
};
const formatted = ts.formatDiagnosticsWithColorAndContext([diagnostic1, diagnostic2], host);
ts.sys.write(formatted + host.getNewLine());