chore: migrate jest-config to TypeScript

[SimenB]

Summary

This isn't ready for merge (of course I'm having issues with normalize...) Help greatly appreciated!

I've purposefully not moved the config types into this package, even though it uses ESM so we would be able to re-export. The reason being the huge dependency tree of jest-config that would be unfortunate to impose on all consumers. Can do something about that after #7738.

Built diff:

diff --git c/packages/jest-config/build/index.js w/packages/jest-config/build/index.js
index 2b3aab25a..8e0049751 100644
--- c/packages/jest-config/build/index.js
+++ w/packages/jest-config/build/index.js
@@ -48,30 +48,30 @@ Object.defineProperty(exports, 'descriptions', {
   }
 });
 
-function _chalk() {
-  const data = _interopRequireDefault(require('chalk'));
+function _fs() {
+  const data = _interopRequireDefault(require('fs'));
 
-  _chalk = function _chalk() {
+  _fs = function _fs() {
     return data;
   };
 
   return data;
 }
 
-function _fs() {
-  const data = _interopRequireDefault(require('fs'));
+function _path() {
+  const data = _interopRequireDefault(require('path'));
 
-  _fs = function _fs() {
+  _path = function _path() {
     return data;
   };
 
   return data;
 }
 
-function _path() {
-  const data = _interopRequireDefault(require('path'));
+function _chalk() {
+  const data = _interopRequireDefault(require('chalk'));
 
-  _path = function _path() {
+  _chalk = function _chalk() {
     return data;
   };
 
@@ -103,8 +103,6 @@ function _interopRequireDefault(obj) {
  *
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
- *
- *
  */
 function readConfig(
   argv,
diff --git c/packages/jest-config/build/normalize.js w/packages/jest-config/build/normalize.js
index 2b0fa4c56..303859c86 100644
--- c/packages/jest-config/build/normalize.js
+++ w/packages/jest-config/build/normalize.js
@@ -617,27 +617,33 @@ function normalize(options, argv, configPath, projectIndex = Infinity) {
       case 'setupFiles':
       case 'setupFilesAfterEnv':
       case 'snapshotSerializers':
-        value =
-          options[key] &&
-          options[key].map(filePath =>
-            (0, _utils.resolve)(newOptions.resolver, {
-              filePath,
-              key,
-              rootDir: options.rootDir
-            })
-          );
+        {
+          const option = options[key];
+          value =
+            option &&
+            option.map(filePath =>
+              (0, _utils.resolve)(newOptions.resolver, {
+                filePath,
+                key,
+                rootDir: options.rootDir
+              })
+            );
+        }
         break;
 
       case 'modulePaths':
       case 'roots':
-        value =
-          options[key] &&
-          options[key].map(filePath =>
-            _path().default.resolve(
-              options.rootDir,
-              (0, _utils.replaceRootDirInPath)(options.rootDir, filePath)
-            )
-          );
+        {
+          const option = options[key];
+          value =
+            option &&
+            option.map(filePath =>
+              _path().default.resolve(
+                options.rootDir,
+                (0, _utils.replaceRootDirInPath)(options.rootDir, filePath)
+              )
+            );
+        }
         break;
 
       case 'collectCoverageFrom':
@@ -646,12 +652,15 @@ function normalize(options, argv, configPath, projectIndex = Infinity) {
 
       case 'cacheDirectory':
       case 'coverageDirectory':
-        value =
-          options[key] &&
-          _path().default.resolve(
-            options.rootDir,
-            (0, _utils.replaceRootDirInPath)(options.rootDir, options[key])
-          );
+        {
+          const option = options[key];
+          value =
+            option &&
+            _path().default.resolve(
+              options.rootDir,
+              (0, _utils.replaceRootDirInPath)(options.rootDir, option)
+            );
+        }
         break;
 
       case 'dependencyExtractor':
@@ -662,36 +671,45 @@ function normalize(options, argv, configPath, projectIndex = Infinity) {
       case 'testResultsProcessor':
       case 'testRunner':
       case 'filter':
-        value =
-          options[key] &&
-          (0, _utils.resolve)(newOptions.resolver, {
-            filePath: options[key],
-            key,
-            rootDir: options.rootDir
-          });
+        {
+          const option = options[key];
+          value =
+            option &&
+            (0, _utils.resolve)(newOptions.resolver, {
+              filePath: option,
+              key,
+              rootDir: options.rootDir
+            });
+        }
         break;
 
       case 'runner':
-        value =
-          options[key] &&
-          (0, _utils.getRunner)(newOptions.resolver, {
-            filePath: options[key],
-            rootDir: options.rootDir
-          });
+        {
+          const option = options[key];
+          value =
+            option &&
+            (0, _utils.getRunner)(newOptions.resolver, {
+              filePath: option,
+              rootDir: options.rootDir
+            });
+        }
         break;
 
       case 'prettierPath':
-        // We only want this to throw if "prettierPath" is explicitly passed
-        // from config or CLI, and the requested path isn't found. Otherwise we
-        // set it to null and throw an error lazily when it is used.
-        value =
-          options[key] &&
-          (0, _utils.resolve)(newOptions.resolver, {
-            filePath: options[key],
-            key,
-            optional: options[key] === _Defaults.default[key],
-            rootDir: options.rootDir
-          });
+        {
+          // We only want this to throw if "prettierPath" is explicitly passed
+          // from config or CLI, and the requested path isn't found. Otherwise we
+          // set it to null and throw an error lazily when it is used.
+          const option = options[key];
+          value =
+            option &&
+            (0, _utils.resolve)(newOptions.resolver, {
+              filePath: option,
+              key,
+              optional: option === _Defaults.default[key],
+              rootDir: options.rootDir
+            });
+        }
         break;
 
       case 'moduleNameMapper':
@@ -784,9 +802,14 @@ function normalize(options, argv, configPath, projectIndex = Infinity) {
         break;
 
       case 'testRegex':
-        value = options[key]
-          ? [].concat(options[key]).map(_jestRegexUtil().replacePathSepForRegex)
-          : [];
+        {
+          const option = options[key];
+          value = option
+            ? (Array.isArray(option) ? option : [option]).map(
+                _jestRegexUtil().replacePathSepForRegex
+              )
+            : [];
+        }
         break;
 
       case 'moduleFileExtensions': {
@@ -820,14 +843,16 @@ function normalize(options, argv, configPath, projectIndex = Infinity) {
       }
 
       case 'bail': {
-        if (typeof options[key] === 'boolean') {
-          value = options[key] ? 1 : 0;
-        } else if (typeof options[key] === 'string') {
+        const bail = options[key];
+
+        if (typeof bail === 'boolean') {
+          value = bail ? 1 : 0;
+        } else if (typeof bail === 'string') {
           value = 1; // If Jest is invoked as `jest --bail someTestPattern` then need to
           // move the pattern from the `bail` configuration and into `argv._`
           // to be processed as an extra parameter
 
-          argv._.push(options[key]);
+          argv._.push(bail);
         } else {
           value = options[key];
         }
@@ -912,7 +937,7 @@ function normalize(options, argv, configPath, projectIndex = Infinity) {
           }
         });
         break;
-    } // $FlowFixMe - automock is missing in GlobalConfig, so what
+    } // @ts-ignore: automock is missing in GlobalConfig, so what
 
     newOptions[key] = value;
     return newOptions;
@@ -921,14 +946,13 @@ function normalize(options, argv, configPath, projectIndex = Infinity) {
   newOptions.testPathPattern = buildTestPathPattern(argv);
   newOptions.json = argv.json;
   newOptions.testFailureExitCode = parseInt(newOptions.testFailureExitCode, 10);
-  var _arr = ['lastCommit', 'changedFilesWithAncestor', 'changedSince'];
-
-  for (var _i = 0; _i < _arr.length; _i++) {
-    const key = _arr[_i];
 
-    if (newOptions[key]) {
-      newOptions.onlyChanged = true;
-    }
+  if (
+    newOptions.lastCommit ||
+    newOptions.changedFilesWithAncestor ||
+    newOptions.changedSince
+  ) {
+    newOptions.onlyChanged = true;
   }
 
   if (argv.all) {
diff --git c/packages/jest-config/build/utils.js w/packages/jest-config/build/utils.js
index 2a3960f98..9ae0774fd 100644
--- c/packages/jest-config/build/utils.js
+++ w/packages/jest-config/build/utils.js
@@ -78,7 +78,7 @@ const resolve = (resolver, {key, filePath, rootDir, optional}) => {
     replaceRootDirInPath(rootDir, filePath),
     {
       basedir: rootDir,
-      resolver
+      resolver: resolver || undefined
     }
   );
 
@@ -158,7 +158,7 @@ const resolveWithPrefix = (
 
   let module = _jestResolve().default.findNodeModule(`${prefix}${fileName}`, {
     basedir: rootDir,
-    resolver
+    resolver: resolver || undefined
   });
 
   if (module) {
@@ -171,7 +171,7 @@ const resolveWithPrefix = (
 
   module = _jestResolve().default.findNodeModule(fileName, {
     basedir: rootDir,
-    resolver
+    resolver: resolver || undefined
   });
 
   if (module) {

Test plan

Green CI (eventually)

[jeysal]

jeysal@ce138f1 fixes most errors in not-too-ugly ways (but has some extracted variables that will cause changes in the build output).
There's two errors remaining that are, I think, really errors that can cause the normalize return value to not match its asserted type.

E.g. detectLeaks is not optional on AllOptions, but I think it might be missing on the returned value.

hasteImplModulePath is not allowed to be null, but it could become null here.

We should decide on some actual structural changes to make that fix especially the first one.

[SimenB]

Thanks again! Cherry-picked it, and did a rebase

E.g. detectLeaks is not optional on AllOptions, but I think it might be missing on the returned value.

It should be set to false if it's not set from argv

hasteImplModulePath is not allowed to be null, but it could become null here.

Than should be allowed to be null (or undefined at least). I wonder if it's left over from #6104? Not sure, but it's definitely allowed to be null as Jest doesn't ship with an implementation and it's not required.

[jeysal]

jeysal@b7caef6 brings DefaultConfig and ProjectConfig closer together, but there's more mismatch in existing keys than expected, so I didn't manage to finish it today. Also, I modified ProjectConfig to allow nullish for dependencyExtractor and moduleLoader, which I think can already have nullish values going out of normalize today, but you should double check.

[SimenB]

Rebased after merging #7964 which also added the Argv typings

[SimenB]

@jeysal I just did 9f9d473 🤷‍♂️ Seems silly to spend too much time on it when we wanna rework the whole thing later. As longs as it works, I'm happy

[jeysal]

@SimenB okay. At least the huge switch is almost properly typed 😄

[SimenB]

If you feel up to it, I'd love a PR removing the cast

[SimenB]

I love it it when types catch a potential bug

[jeysal]

Don't think it really makes sense to, when I tried to go through the mismatching keys it felt like I was just guessing which keys were allowed to be nullish going out of normalize etc...

[codecov-io]

Codecov Report

Merging #7944 into master will decrease coverage by 0.29%.
The diff coverage is 85.26%.

@@            Coverage Diff            @@
##           master    #7944     +/-   ##
=========================================
- Coverage   64.54%   64.24%   -0.3%     
=========================================
  Files         257      258      +1     
  Lines       10074    10117     +43     
  Branches     1587     1742    +155     
=========================================
- Hits         6502     6500      -2     
- Misses       3229     3234      +5     
- Partials      343      383     +40

Impacted Files	Coverage Δ
packages/jest-config/src/setFromArgv.ts	85.71% <ø> (ø)
packages/jest-config/src/validatePattern.ts	100% <ø> (ø)
...ckages/jest-config/src/ReporterValidationErrors.ts	11.76% <ø> (ø)
...ges/jest-config/src/readConfigFileAndSetRootDir.ts	0% <ø> (ø)
packages/jest-config/src/constants.ts	100% <ø> (ø)
packages/jest-config/src/getCacheDirectory.ts	66.66% <ø> (ø)
packages/jest-runner/src/runTest.ts	2.53% <0%> (-0.07%)	⬇️
packages/jest-config/src/getMaxWorkers.ts	100% <100%> (ø)
packages/jest-config/src/Defaults.ts	100% <100%> (ø)
packages/jest-config/src/resolveConfigPath.ts	90.9% <100%> (ø)
... and 12 more

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