Lazy_mode_utils.focus_and_check failed to process updates

Summary:
`Rechecker.process_updates` does a bunch of really useful
things, like detecting whether the Flow server needs to crash and
filtering out ignored files. `Lazy_mode_utils.focus_and_check` wasn't
calling it, and so you could trick a Flow server into checking a lazy
file.

Reviewed By: nmote

Differential Revision: D7493998

fbshipit-source-id: 85b90f312b99c1f2d5518e9c8bb310dad3a26ca6

Author: gabelevi

newtests/ide/lazy/_flowconfig

@@ -1,4 +1,5 @@
 [ignore]
+<PROJECT_ROOT>/ignored\.js
 
 [include]
 

newtests/ide/lazy/ignored.js

@@ -0,0 +1 @@
+var x: string = 123;

newtests/ide/lazy/test.js

@@ -9,6 +9,82 @@ import {suite, test} from 'flow-dev-tools/src/test/Tester';
 export default suite(({
   addCode, addFile, addFiles, removeFile, ideStart, ideNotification, flowCmd
 }) => [
+  test('Opening and closing ignored file', [
+    ideStart()
+      .ideNotification('subscribeToDiagnostics')
+      .ideNewMessagesWithTimeout(
+        10000,
+        [
+          {
+            "method": "diagnosticsNotification",
+            "params": [
+              {
+                "flowVersion": "<VERSION STUBBED FOR TEST>",
+                "jsonVersion": "1",
+                "errors": [],
+                "passed": true
+              }
+            ]
+          }
+        ],
+      ),
+
+    addFile('ignored.js')
+      .ideNoNewMessagesAfterSleep(500)
+      .noNewErrors()
+      .because('The IDE has not opened ignored.js yet'),
+
+    ideNotification('didOpen', 'ignored.js')
+      .ideNewMessagesWithTimeout(
+        50000,
+        [
+          {
+            "method": "diagnosticsNotification",
+            "params": [
+              {
+                "flowVersion": "<VERSION STUBBED FOR TEST>",
+                "jsonVersion": "1",
+                "errors": [],
+                "passed": true
+              }
+            ]
+          }
+        ],
+      )
+      .because('The file is ignored'),
+
+    ideNotification('didClose', 'ignored.js')
+      .ideNewMessagesWithTimeout(
+        50000,
+        [
+          {
+            "method": "diagnosticsNotification",
+            "params": [
+              {
+                "flowVersion": "<VERSION STUBBED FOR TEST>",
+                "jsonVersion": "1",
+                "errors": [],
+                "passed": true
+              }
+            ]
+          }
+        ],
+      )
+      .because('Closing the file does not trigger recheck, just sends errors'),
+
+    flowCmd(['status', '--strip-root'])
+      .stdout(
+        `
+          No errors!
+
+          The Flow server is currently in IDE lazy mode and is only checking 0/1 files.
+          To learn more, visit flow.org/en/docs/lang/lazy-modes
+
+        `,
+      )
+      .because('Still no errors'),
+  ]).lazy('ide'),
+
   test('Opening and closing single file with no dependents or dependencies', [
     ideStart()
       .ideNotification('subscribeToDiagnostics')

src/server/lazy_mode_utils.ml

@@ -9,13 +9,8 @@ open ServerEnv
 open Utils_js
 
 let focus_and_check genv env filenames =
-  let options = genv.options in
-  let file_options = Options.file_options options in
-  let focused = Nel.fold_left
-    (fun acc fn ->
-      FilenameSet.add (Files.filename_from_string ~options:file_options fn) acc)
-    FilenameSet.empty
-    filenames in
+  let filenames = SSet.of_list (Nel.to_list filenames) in
+  let focused = Rechecker.process_updates genv env filenames in
   let checked_files = CheckedSet.add ~focused env.checked_files in
 
   let new_focused_files = focused