crypto: Allow only a identity to be verified when the verification finishes

QR code based verification doesn't verify a device when users are
verifying each other, generalize the logic that marks stuff as verified
so we can verify either only a device or an user identity or both.

matrix_sdk_crypto/src/verification/mod.rs

@@ -43,7 +43,7 @@ use tracing::{error, info, trace, warn};
 use crate::{
     error::SignatureError,
     olm::PrivateCrossSigningIdentity,
-    store::{Changes, CryptoStore, DeviceChanges},
+    store::{Changes, CryptoStore},
     CryptoStoreError, LocalTrust, ReadOnlyDevice, UserIdentities,
 };
 
@@ -257,9 +257,18 @@ impl IdentitiesBeingVerified {
         verified_devices: Option<&[ReadOnlyDevice]>,
         verified_identities: Option<&[UserIdentities]>,
     ) -> Result<VerificationResult, CryptoStoreError> {
-        if let Some(device) = self.mark_device_as_verified(verified_devices).await? {
+        let device = self.mark_device_as_verified(verified_devices).await?;
         let identity = self.mark_identity_as_verified(verified_identities).await?;
 
+        if device.is_none() && identity.is_none() {
+            // Something wen't wrong if nothing was verified, we use key
+            // mismatch here, since it's the closest to nothing was verified
+            return Ok(VerificationResult::Cancel(CancelCode::KeyMismatch));
+        }
+
+        let mut changes = Changes::default();
+
+        let signature_request = if let Some(device) = device {
             // We only sign devices of our own user here.
             let signature_request = if device.user_id() == self.user_id() {
                 match self.private_identity.sign_device(&device).await {
@@ -288,9 +297,10 @@ impl IdentitiesBeingVerified {
                 None
             };
 
-            let mut changes = Changes {
-                devices: DeviceChanges { changed: vec![device], ..Default::default() },
-                ..Default::default()
+            changes.devices.changed.push(device);
+            signature_request
+        } else {
+            None
         };
 
         let identity_signature_request = if let Some(i) = identity {
@@ -321,7 +331,6 @@ impl IdentitiesBeingVerified {
             };
 
             changes.identities.changed.push(i);
-
             request
         } else {
             None
@@ -345,12 +354,10 @@ impl IdentitiesBeingVerified {
 
         // TODO store the signature upload request as well.
         self.store.save_changes(changes).await?;
+
         Ok(merged_request
             .map(VerificationResult::SignatureUpload)
             .unwrap_or(VerificationResult::Ok))
-        } else {
-            Ok(VerificationResult::Cancel(CancelCode::UserMismatch))
-        }
     }
 
     async fn mark_identity_as_verified(