bug symfony#58274 [Dotenv] throw a meaningful exception when parsing dotenv files with BOM (xabbuh)

This PR was merged into the 5.4 branch.

Discussion
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[Dotenv] throw a meaningful exception when parsing dotenv files with BOM

| Q             | A
| ------------- | ---
| Branch?       | 5.4
| Bug fix?      | yes
| New feature?  | no
| Deprecations? | no
| Issues        | Fix symfony#58214
| License       | MIT

This replaces symfony#58216. Other than in that PR I did not account for UTF-16 and UTF-32 byte-order-mark variants as that would IMO require us to first reliably detect the file encoding.

Commits
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b4f3eaa throw a meaningful exception when parsing dotenv files with BOM

Author: nicolas-grekas

src/Symfony/Component/Dotenv/Dotenv.php

@@ -568,7 +568,13 @@ private function doLoad(bool $overrideExistingVars, array $paths): void
                 throw new PathException($path);
             }
 
-            $this->populate($this->parse(file_get_contents($path), $path), $overrideExistingVars);
+            $data = file_get_contents($path);
+
+            if ("\xEF\xBB\xBF" === substr($data, 0, 3)) {
+                throw new FormatException('Loading files starting with a byte-order-mark (BOM) is not supported.', new FormatExceptionContext($data, $path, 1, 0));
+            }
+
+            $this->populate($this->parse($data, $path), $overrideExistingVars);
         }
     }
 }

src/Symfony/Component/Dotenv/Tests/DotenvTest.php

@@ -604,4 +604,14 @@ public function testBootEnv()
         $resetContext();
         rmdir($tmpdir);
     }
+
+    public function testExceptionWithBom()
+    {
+        $dotenv = new Dotenv();
+
+        $this->expectException(FormatException::class);
+        $this->expectExceptionMessage('Loading files starting with a byte-order-mark (BOM) is not supported.');
+
+        $dotenv->load(__DIR__.'/fixtures/file_with_bom');
+    }
 }

src/Symfony/Component/Dotenv/Tests/fixtures/file_with_bom

@@ -0,0 +1 @@
+FOO=BAR