From 4286919b0635fdbe56b80493a7d6201cefce4f6d Mon Sep 17 00:00:00 2001
From: "Matt.Gooding" <869053+mgooding@users.noreply.github.com>
Date: Mon, 21 Mar 2022 11:00:56 -0400
Subject: [PATCH 1/3] Better error when hubAccess is undefined

---
 core/backend/src/IModelHost.ts           | 10 +++++++++-
 core/backend/src/test/HubMock.ts         |  6 +++++-
 core/backend/src/test/IModelHost.test.ts |  5 +++++
 3 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/core/backend/src/IModelHost.ts b/core/backend/src/IModelHost.ts
index a0e847bbff54..674073694ba2 100644
--- a/core/backend/src/IModelHost.ts
+++ b/core/backend/src/IModelHost.ts
@@ -322,7 +322,15 @@ export class IModelHost {
   /** Provides access to the IModelHub for this IModelHost
    * @beta
    */
-  public static get hubAccess(): BackendHubAccess { return this._hubAccess; }
+  public static get hubAccess(): BackendHubAccess {
+    // Strictly speaking, _hubAccess should be marked as possibly undefined since it's not needed for Snapshot iModels.
+    // However, a decision was made to not provide that type annotation so callers aren't forced to constantly check for
+    // something that's required in all other workflows.
+    // This check is here to provide a better error message when hubAccess is inadvertently undefined.
+    if (this._hubAccess === undefined)
+      throw new IModelError(IModelStatus.BadRequest, "IModelHost.hubAccess is undefined. Specify an implementation in your IModelHostConfiguration");
+    return this._hubAccess;
+  }
 
   private static _isValid = false;
   /** Returns true if IModelHost is started.  */
diff --git a/core/backend/src/test/HubMock.ts b/core/backend/src/test/HubMock.ts
index 84704355b9cb..278b2f5da9d8 100644
--- a/core/backend/src/test/HubMock.ts
+++ b/core/backend/src/test/HubMock.ts
@@ -80,7 +80,11 @@ export class HubMock {
     this.mockRoot = join(KnownTestLocations.outputDir, "HubMock", mockName);
     IModelJsFs.recursiveMkDirSync(this.mockRoot);
     IModelJsFs.purgeDirSync(this.mockRoot);
-    this._saveHubAccess = IModelHost.hubAccess;
+    try {
+      this._saveHubAccess = IModelHost.hubAccess;
+    } catch (error) {
+      // See note in IModelHost.hubAccess. hubAccess can in fact be undefined, but that is not annotated in type system.
+    }
     IModelHost.setHubAccess(this);
     HubMock._iTwinId = Guid.createValue(); // all iModels for this test get the same "iTwinId"
   }
diff --git a/core/backend/src/test/IModelHost.test.ts b/core/backend/src/test/IModelHost.test.ts
index c0d064fdd6ca..0834b1d80780 100644
--- a/core/backend/src/test/IModelHost.test.ts
+++ b/core/backend/src/test/IModelHost.test.ts
@@ -192,4 +192,9 @@ describe("IModelHost", () => {
 
   });
 
+  it("should throw if hubAccess is undefined and getter is called", async () => {
+    await IModelHost.startup();
+    expect(() => IModelHost.hubAccess).throws("IModelHost.hubAccess is undefined. Specify an implementation in your IModelHostConfiguration");
+  });
+
 });

From ee0a0a3c92d7f83c27c2afb61b0b6610ad9a90b7 Mon Sep 17 00:00:00 2001
From: "Matt.Gooding" <869053+mgooding@users.noreply.github.com>
Date: Mon, 21 Mar 2022 11:18:10 -0400
Subject: [PATCH 2/3] rush change

---
 .../error-on-no-hub-access_2022-03-21-15-17.json       | 10 ++++++++++
 1 file changed, 10 insertions(+)
 create mode 100644 common/changes/@itwin/core-backend/error-on-no-hub-access_2022-03-21-15-17.json

diff --git a/common/changes/@itwin/core-backend/error-on-no-hub-access_2022-03-21-15-17.json b/common/changes/@itwin/core-backend/error-on-no-hub-access_2022-03-21-15-17.json
new file mode 100644
index 000000000000..cdc12470b55d
--- /dev/null
+++ b/common/changes/@itwin/core-backend/error-on-no-hub-access_2022-03-21-15-17.json
@@ -0,0 +1,10 @@
+{
+  "changes": [
+    {
+      "packageName": "@itwin/core-backend",
+      "comment": "Improved error message for undefined IModelHost.hubAccess",
+      "type": "none"
+    }
+  ],
+  "packageName": "@itwin/core-backend"
+}
\ No newline at end of file

From ec88a1e49aacec829a98e0a6080944a7abfc23b5 Mon Sep 17 00:00:00 2001
From: "Matt.Gooding" <869053+mgooding@users.noreply.github.com>
Date: Mon, 21 Mar 2022 11:42:16 -0400
Subject: [PATCH 3/3] Document IModelHost.hubAccess throwing if backing value
 is undefined

---
 core/backend/src/IModelHost.ts | 1 +
 1 file changed, 1 insertion(+)

diff --git a/core/backend/src/IModelHost.ts b/core/backend/src/IModelHost.ts
index 674073694ba2..e2db6152dfa2 100644
--- a/core/backend/src/IModelHost.ts
+++ b/core/backend/src/IModelHost.ts
@@ -321,6 +321,7 @@ export class IModelHost {
 
   /** Provides access to the IModelHub for this IModelHost
    * @beta
+   * @note If [[IModelHostConfiguration.hubAccess]] was undefined when initializing this class, accessing this property will throw an error.
    */
   public static get hubAccess(): BackendHubAccess {
     // Strictly speaking, _hubAccess should be marked as possibly undefined since it's not needed for Snapshot iModels.