Fix master, add back retainLines to ./.babelrc

[rickhanlonii]

Summary

This PR fixes master by rolling back the retainLines change

It looks like removing the retainLines gave the integration tests the wrong line number. For example in this test (and the rest from what I could tell), the snapshot is correct:

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@@            Coverage Diff            @@
##             master    #5449   +/-   ##
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  Coverage          ?   62.18%           
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  Files             ?      205           
  Lines             ?     6928           
  Branches          ?        3           
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  Hits              ?     4308           
  Misses            ?     2619           
  Partials          ?        1

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[cpojer]

Oh, the right fix would be to fix up all the tests instead. cc @jessecarfb

[rickhanlonii]

I looked into that and I think the tests are actually correct as they are written. Updating the tests would assert that the line numbers don't match the actual file lines

Also this is just the retainLines that I changed, I kept @jessecarfb's change

[SimenB]

This change shouldn't be needed - I wonder if the stack trace is wrong?

[SimenB]

The issue is that the sourcemap is not applied - #5177 might fix this. This diff fixes most of the test suite for me locally, except for tests related to mapCoverage and a couple other (I haven't dug into it). All stack traces are correct at least.

diff --git c/packages/babel-jest/src/index.js w/packages/babel-jest/src/index.js
index 647b56a1..593041c5 100644
--- c/packages/babel-jest/src/index.js
+++ w/packages/babel-jest/src/index.js
@@ -69,7 +69,7 @@ const createTransformer = (options: any) => {
   options = Object.assign({}, options, {
     plugins: (options && options.plugins) || [],
     presets: ((options && options.presets) || []).concat([jestPreset]),
-    sourceMaps: 'inline',
+    sourceMaps: 'both',
   });
   delete options.cacheDirectory;
   delete options.filename;
@@ -128,7 +128,7 @@ const createTransformer = (options: any) => {
 
       // babel v7 might return null in the case when the file has been ignored.
       const transformResult = babelTransform(src, theseOptions);
-      return transformResult ? transformResult.code : src;
+      return transformResult || src;
     },
   };
 };
diff --git c/packages/jest-runtime/src/script_transformer.js w/packages/jest-runtime/src/script_transformer.js
index 9cd85d27..bfcc4792 100644
--- c/packages/jest-runtime/src/script_transformer.js
+++ w/packages/jest-runtime/src/script_transformer.js
@@ -242,12 +242,10 @@ export default class ScriptTransformer {
       }
     }
 
-    if (mapCoverage) {
-      if (!transformed.map) {
-        const inlineSourceMap = convertSourceMap.fromSource(transformed.code);
-        if (inlineSourceMap) {
-          transformed.map = inlineSourceMap.toJSON();
-        }
+    if (!transformed.map) {
+      const inlineSourceMap = convertSourceMap.fromSource(transformed.code);
+      if (inlineSourceMap) {
+        transformed.map = inlineSourceMap.toJSON();
       }
     }
 
@@ -261,7 +259,7 @@ export default class ScriptTransformer {
       code = transformed.code;
     }
 
-    if (instrument && mapCoverage && transformed.map) {
+    if (transformed.map) {
       const sourceMapContent =
         typeof transformed.map === 'string'
           ? transformed.map

The return transformResult || src; part is a breaking change in babel-jest (not for Jest as it supports both forms, but for programmatic usage of it), but maybe we can put it behind an option?

[SimenB]

I vote for merging this to fix master, and looking into dropping it later

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