[CQ] fix nullability problems for flutter/bazel (#8296)

Fix nullability problems in `src/io/flutter/bazel/`.

See #8291.

If we pursue #8292, we
could mark `src/io/flutter/bazel/` as null-"clean".


---

- [x] I’ve reviewed the contributor guide and applied the relevant
portions to this PR.

<details>
  <summary>Contribution guidelines:</summary><br>

- See our [contributor
guide]([https://github.com/dart-lang/sdk/blob/main/CONTRIBUTING.md](https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#overview)
for general expectations for PRs.
- Larger or significant changes should be discussed in an issue before
creating a PR.
- Dart contributions to our repos should follow the [Dart style
guide](https://dart.dev/guides/language/effective-dart) and use `dart
format`.
- Java and Kotlin contributions should strive to follow Java and Kotlin
best practices
([discussion](#8098)).
</details>

Author: pq

flutter-idea/src/io/flutter/bazel/PluginConfig.java

@@ -113,10 +113,11 @@ public static PluginConfig load(@NotNull VirtualFile file) {
     final Computable<PluginConfig> readAction = () -> {
       try (
         // Create the input stream in a try-with-resources statement. This will automatically close the stream
-        // in an implicit finally section; this addresses a file handle leak issue we had on MacOS.
+        // in an implicit finally section; this addresses a file handle leak issue we had on macOS.
         final InputStreamReader input = new InputStreamReader(file.getInputStream(), StandardCharsets.UTF_8)
       ) {
         final Fields fields = GSON.fromJson(input, Fields.class);
+        assert fields != null;
         return new PluginConfig(fields);
       }
       catch (FileNotFoundException e) {
@@ -142,7 +143,7 @@ public static PluginConfig load(@NotNull VirtualFile file) {
   }
 
   @VisibleForTesting
-  public static PluginConfig forTest(
+  public static @NotNull PluginConfig forTest(
     @Nullable String daemonScript,
     @Nullable String devToolsScript,
     @Nullable String doctorScript,
@@ -181,86 +182,86 @@ private static class Fields {
      * The script to run to start 'flutter daemon'.
      */
     @SerializedName("daemonScript")
-    private String daemonScript;
+    private @Nullable String daemonScript;
 
     @SerializedName("devToolsScript")
-    private String devToolsScript;
+    private @Nullable String devToolsScript;
 
     /**
      * The script to run to start 'flutter doctor'.
      */
     @SerializedName("doctorScript")
-    private String doctorScript;
+    private @Nullable String doctorScript;
 
     /**
      * The script to run to start 'flutter test'
      */
     @SerializedName("testScript")
-    private String testScript;
+    private @Nullable String testScript;
 
     /**
      * The script to run to start 'flutter run'
      */
     @SerializedName("runScript")
-    private String runScript;
+    private @Nullable String runScript;
 
     /**
      * The script to run to start 'flutter sync'
      */
     @SerializedName("syncScript")
-    private String syncScript;
+    private @Nullable String syncScript;
 
     @SerializedName("toolsScript")
-    private String toolsScript;
+    private @Nullable String toolsScript;
 
     /**
      * The directory containing the SDK tools.
      */
     @SerializedName("sdkHome")
-    private String sdkHome;
+    private @Nullable String sdkHome;
 
     /**
      * The file containing the Flutter version.
      */
     @SerializedName("requiredIJPluginID")
-    private String requiredIJPluginID;
+    private @Nullable String requiredIJPluginID;
 
     /**
      * The file containing the message to install the required IJ Plugin.
      */
     @SerializedName("requiredIJPluginMessage")
-    private String requiredIJPluginMessage;
+    private @Nullable String requiredIJPluginMessage;
 
     /**
      * The prefix that indicates a configuration warning message.
      */
     @SerializedName("configWarningPrefix")
-    private String configWarningPrefix;
+    private @Nullable String configWarningPrefix;
 
     /**
      * The prefix that indicates a message about iOS run being updated.
      */
     @SerializedName("updatedIosRunMessage")
-    private String updatedIosRunMessage;
+    private @Nullable String updatedIosRunMessage;
 
     Fields() {
     }
 
     /**
      * Convenience constructor that takes all parameters.
      */
-    Fields(String daemonScript,
-           String devToolsScript,
-           String doctorScript,
-           String testScript,
-           String runScript,
-           String syncScript,
-           String toolsScript,
-           String sdkHome,
-           String requiredIJPluginID,
-           String requiredIJPluginMessage,
-           String configWarningPrefix,
-           String updatedIosRunMessage) {
+    Fields(@Nullable String daemonScript,
+           @Nullable String devToolsScript,
+           @Nullable String doctorScript,
+           @Nullable String testScript,
+           @Nullable String runScript,
+           @Nullable String syncScript,
+           @Nullable String toolsScript,
+           @Nullable String sdkHome,
+           @Nullable String requiredIJPluginID,
+           @Nullable String requiredIJPluginMessage,
+           @Nullable String configWarningPrefix,
+           @Nullable String updatedIosRunMessage) {
       this.daemonScript = daemonScript;
       this.devToolsScript = devToolsScript;
       this.doctorScript = doctorScript;
@@ -298,6 +299,6 @@ public int hashCode() {
     }
   }
 
-  private static final Gson GSON = new Gson();
+  private static final @NotNull Gson GSON = new Gson();
   private static final @NotNull Logger LOG = Logger.getInstance(PluginConfig.class);
 }

flutter-idea/src/io/flutter/bazel/Workspace.java

@@ -274,6 +274,7 @@ static Workspace loadUncached(@NotNull Project project) {
     if (workspaceFile == null) return null;
 
     final VirtualFile root = workspaceFile.getParent();
+    if (root == null) return null;
     final String readonlyPath = "../READONLY/" + root.getName();
     final VirtualFile readonlyRoot = root.findFileByRelativePath(readonlyPath);
     VirtualFile configFile = root.findFileByRelativePath(PLUGIN_CONFIG_PATH);
@@ -313,7 +314,7 @@ static Workspace loadUncached(@NotNull Project project) {
   }
 
   @VisibleForTesting
-  public static Workspace forTest(VirtualFile workspaceRoot, PluginConfig pluginConfig) {
+  public static Workspace forTest(@NotNull VirtualFile workspaceRoot, @NotNull PluginConfig pluginConfig) {
     return new Workspace(
       workspaceRoot,
       pluginConfig,
@@ -339,7 +340,9 @@ public static Workspace forTest(VirtualFile workspaceRoot, PluginConfig pluginCo
    * @param relativeScriptPath the relative path to the desired script inside of the workspace.
    * @return the script's path relative to the workspace, or null if it was not found.
    */
-  private static String getScriptFromPath(@NotNull VirtualFile root, @NotNull String readonlyPath, @Nullable String relativeScriptPath) {
+  private static @Nullable String getScriptFromPath(@NotNull VirtualFile root,
+                                                    @NotNull String readonlyPath,
+                                                    @Nullable String relativeScriptPath) {
     if (relativeScriptPath == null) {
       return null;
     }
@@ -363,8 +366,12 @@ private static String getScriptFromPath(@NotNull VirtualFile root, @NotNull Stri
   @Nullable
   private static VirtualFile findWorkspaceFile(@NotNull Project p) {
     final Computable<VirtualFile> readAction = () -> {
+      ProjectRootManager rootManager = ProjectRootManager.getInstance(p);
+      if (rootManager == null) return null;
+      
       final Map<String, VirtualFile> candidates = new HashMap<>();
-      for (VirtualFile contentRoot : ProjectRootManager.getInstance(p).getContentRoots()) {
+      for (VirtualFile contentRoot : rootManager.getContentRoots()) {
+        if (contentRoot == null) continue;
         final VirtualFile wf = findContainingWorkspaceFile(contentRoot);
         if (wf != null) {
           candidates.put(wf.getPath(), wf);
@@ -404,7 +411,7 @@ private static VirtualFile findContainingWorkspaceFile(@NotNull VirtualFile dir)
     return null;
   }
 
-  public String convertPath(String path) {
+  public String convertPath(@NotNull String path) {
     if (path.startsWith(Workspace.BAZEL_URI_SCHEME)) {
       return getRoot().getPath() + path.substring(Workspace.BAZEL_URI_SCHEME.length());
     }