esbuild-{es,style}lint-plugin.js: Fix error behaviour

Properly report errors. Unfortunately errors cause eslint watch mode to
abort the watch loop, so add a hack to reduce them to warnings in watch
mode. Warnings don't fail a normal "npm run build" [1], so we have to
make this dynamic for now.

[1] eslint/eslint#16804

esbuild-eslint-plugin.js

@@ -4,8 +4,10 @@
 
 import { ESLint } from 'eslint';
 
+const NAME = 'eslintPlugin';
+
 export const eslintPlugin = {
-    name: 'eslintPlugin',
+    name: NAME,
     setup(build) {
         const filesToLint = [];
         const eslint = new ESLint();
@@ -20,9 +22,14 @@ export const eslintPlugin = {
             const formatter = await eslint.loadFormatter('stylish');
             const output = formatter.format(result);
             if (output.length > 0) {
-                // eslint-disable-next-line no-console
-                console.log(output);
+                console.log(output); // eslint-disable no-console
+                // HACK: errors abort watch mode, but warnings don't fail build
+                const key = (process.env.ESBUILD_WATCH === "true") ? 'warnings' : 'errors';
+                return {
+                    [key]: [{ pluginName: NAME, text: 'ESLint errors found' }]
+                };
             }
+            return null;
         });
     },
 };

esbuild-stylelint-plugin.js

@@ -3,11 +3,13 @@
 import * as stylelint from 'stylelint';
 import * as formatter from 'stylelint-formatter-pretty';
 
+const NAME = 'stylelintPlugin';
+
 export const stylelintPlugin = ({
     filter = /\.(s?css)$/,
     ...stylelintOptions
 } = {}) => ({
-    name: 'stylelintPlugin',
+    name: NAME,
     setup(build) {
         const targetFiles = [];
         build.onLoad({ filter }, ({ path }) => {
@@ -24,8 +26,14 @@ export const stylelintPlugin = ({
             });
             const { output } = result;
             if (output.length > 0) {
-                console.log(output);
+                console.log(output); // eslint-disable no-console
+                // HACK: errors abort watch mode, but warnings don't fail build
+                const key = (process.env.ESBUILD_WATCH === "true") ? 'warnings' : 'errors';
+                return {
+                    [key]: [{ pluginName: NAME, text: 'stylelint errors found' }]
+                };
             }
+            return null;
         });
     }
 });