Flask devx fix (#13280)

* added fix for snaps devx issue

* reordered lines

* updated comment

* added test that ensures removeFencedCode detects a file with sourceMap inclusion

* fixed test

* Update development/build/transforms/remove-fenced-code.test.js

Co-authored-by: Erik Marks <25517051+rekmarks@users.noreply.github.com>

development/build/transforms/remove-fenced-code.js

@@ -200,9 +200,19 @@ const directiveParsingRegex = /^([A-Z]+):([A-Z_]+)(?:\(((?:\w+,)*\w+)\))?$/u;
  * a boolean indicating whether they were modified.
  */
 function removeFencedCode(filePath, typeOfCurrentBuild, fileContent) {
-  const matchedLines = [...fileContent.matchAll(linesWithFenceRegex)];
+  // Do not modify the file if we detect an inline sourcemap. For reasons
+  // yet to be determined, the transform receives every file twice while in
+  // watch mode, the second after Babel has transpiled the file. Babel adds
+  // inline source maps to the file, something we will never do in our own
+  // source files, so we use the existence of inline source maps to determine
+  // whether we should ignore the file.
+  if (/^\/\/# sourceMappingURL=/gmu.test(fileContent)) {
+    return [fileContent, false];
+  }
 
   // If we didn't match any lines, return the unmodified file contents.
+  const matchedLines = [...fileContent.matchAll(linesWithFenceRegex)];
+
   if (matchedLines.length === 0) {
     return [fileContent, false];
   }

development/build/transforms/remove-fenced-code.test.js

@@ -610,6 +610,17 @@ describe('build/transforms/remove-fenced-code', () => {
       });
     });
 
+    it('ignores files with inline source maps', () => {
+      // This is so that there isn't an unnecessary second execution of
+      // removeFencedCode with a transpiled version of the same file
+      const input = getTestData().validInputs.extraContentWithFences.concat(
+        '\n//# sourceMappingURL=as32e32wcwc2234f2ew32cnin4243f4nv9nsdoivnxzoivnd',
+      );
+      expect(
+        removeFencedCode(mockFileName, BuildType.flask, input),
+      ).toStrictEqual([input, false]);
+    });
+
     // We can't do this until there's more than one command
     it.todo('rejects directive pairs with mismatched commands');
   });