fix: plugin warnings not showing warning.loc

cli/run/batchWarnings.ts

@@ -189,8 +189,9 @@ const deferredHandlers: {
 				for (const warning of items) {
 					if (warning.url && warning.url !== lastUrl) info((lastUrl = warning.url));
 
-					if (warning.id) {
-						let loc = relativeId(warning.id);
+					const id = warning.id || warning.loc?.file;
+					if (id) {
+						let loc = relativeId(id);
 						if (warning.loc) {
 							loc += `: (${warning.loc.line}:${warning.loc.column})`;
 						}

test/cli/samples/warn-plugin-loc/_config.js

@@ -0,0 +1,17 @@
+const { assertIncludes } = require('../../../utils.js');
+
+module.exports = {
+	description: 'correctly adds locations to plugin warnings',
+	command: 'rollup -c',
+	stderr: stderr => {
+		assertIncludes(
+			stderr,
+			'(!) Plugin test: Warning with file and id\n' +
+				'file1: (1:2)\n' +
+				'(!) Plugin test: Warning with file\n' +
+				'file2: (2:3)\n' +
+				'(!) Plugin test: Warning with id\n' +
+				'file-id3: (3:4)\n'
+		);
+	}
+};

test/cli/samples/warn-plugin-loc/main.js

@@ -0,0 +1 @@
+console.log("everyday I'm throwing");

test/cli/samples/warn-plugin-loc/rollup.config.js

@@ -0,0 +1,29 @@
+const path = require('path');
+
+module.exports = {
+	input: 'main.js',
+	output: {
+		format: 'cjs'
+	},
+	plugins: [
+		{
+			name: 'test',
+			buildStart() {
+				this.warn({
+					message: 'Warning with file and id',
+					file: path.join(__dirname, 'file-id1'),
+					loc: { file: path.join(__dirname, 'file1'), line: 1, column: 2 }
+				});
+				this.warn({
+					message: 'Warning with file',
+					loc: { file: path.join(__dirname, 'file2'), line: 2, column: 3 }
+				});
+				this.warn({
+					message: 'Warning with id',
+					id: path.join(__dirname, 'file-id3'),
+					loc: { line: 3, column: 4 }
+				});
+			}
+		}
+	]
+};