syn2mas: fix handling of Synapse user_consent config

Closes #3928

Author: reivilibre

crates/syn2mas/src/synapse_reader/checks.rs

@@ -136,7 +136,7 @@ pub fn synapse_config_check(synapse_config: &Config) -> (Vec<CheckWarning>, Vec<
     if synapse_config.enable_registration {
         warnings.push(CheckWarning::DisableRegistrationAfterMigration);
     }
-    if synapse_config.user_consent {
+    if synapse_config.user_consent.is_some() {
         warnings.push(CheckWarning::DisableUserConsentAfterMigration);
     }
 
@@ -232,7 +232,7 @@ pub async fn synapse_config_check_against_mas_config(
     }
 
     let mas_branding = BrandingConfig::extract_or_default(mas)?;
-    if synapse.user_consent && mas_branding.tos_uri.is_none() {
+    if synapse.user_consent.is_some() && mas_branding.tos_uri.is_none() {
         warnings.push(CheckWarning::ShouldPortUserConsentAsTerms);
     }
 

crates/syn2mas/src/synapse_reader/config.rs

@@ -36,7 +36,7 @@ pub struct Config {
     pub enable_3pid_changes: bool,
 
     #[serde(default)]
-    pub user_consent: bool,
+    pub user_consent: Option<UserConsentSection>,
 
     #[serde(default)]
     pub registrations_require_3pid: Vec<String>,
@@ -297,3 +297,8 @@ mod test {
         );
     }
 }
+
+/// We don't care about any of the fields in this section,
+/// just whether it's present.
+#[derive(Deserialize)]
+pub struct UserConsentSection {}