verify: add Debug bound to ServerCertVerifier

This commit adds a `Debug` bound to the `ServerCertVerifier` trait in
addition to `Send` and `Sync`. Types implementing this trait are updated
to either derive `Debug` or implement it by hand as appropriate.

examples/src/bin/tlsclient-mio.rs

@@ -315,6 +315,7 @@ mod danger {
     use rustls::client::WebPkiServerVerifier;
     use rustls::DigitallySignedStruct;
 
+    #[derive(Debug)]
     pub struct NoCertificateVerification {}
 
     impl rustls::client::danger::ServerCertVerifier for NoCertificateVerification {

rustls/examples/internal/bogo_shim.rs

@@ -241,6 +241,7 @@ impl server::danger::ClientCertVerifier for DummyClientAuth {
     }
 }
 
+#[derive(Debug)]
 struct DummyServerAuth {}
 
 impl client::danger::ServerCertVerifier for DummyServerAuth {

rustls/src/verify.rs

@@ -67,7 +67,7 @@ impl ClientCertVerified {
 /// Something that can verify a server certificate chain, and verify
 /// signatures made by certificates.
 #[allow(unreachable_pub)]
-pub trait ServerCertVerifier: Send + Sync {
+pub trait ServerCertVerifier: Debug + Send + Sync {
     /// Verify the end-entity certificate `end_entity` is valid for the
     /// hostname `dns_name` and chains to at least one trust anchor.
     ///

rustls/src/webpki/server_verifier.rs

@@ -112,6 +112,7 @@ impl ServerCertVerifierBuilder {
 
 /// Default `ServerCertVerifier`, see the trait impl for more information.
 #[allow(unreachable_pub)]
+#[derive(Debug)]
 pub struct WebPkiServerVerifier {
     roots: Arc<RootCertStore>,
     crls: Vec<CertRevocationList<'static>>,

rustls/tests/server_cert_verifier.rs

@@ -154,6 +154,7 @@ fn client_can_override_certificate_verification_and_offer_no_signature_schemes()
     }
 }
 
+#[derive(Debug)]
 pub struct MockServerVerifier {
     cert_rejection_error: Option<Error>,
     tls12_signature_error: Option<Error>,