openpgp: Make conversions into Key<SecretParts, _> fallible.

  - Fixes #380.

2 files changed, 13 insertions, 9 deletions

diff --git a/guide/src/chapter_01.md b/guide/src/chapter_01.md
index 5c9d177f..b2b143bb 100644
--- a/guide/src/chapter_01.md
+++ b/guide/src/chapter_01.md
@@ -10,6 +10,7 @@ fragments yields the [`openpgp/examples/generate-sign-verify.rs`].
 
 ```rust
 use std::io::{self, Write};
+use std::convert::TryInto;
 
 extern crate failure;
 extern crate sequoia_openpgp as openpgp;
@@ -51,7 +52,7 @@ fn main() {
 #            -> openpgp::Result<()> {
 #     // Get the keypair to do the signing from the TPK.
 #     let key : key::UnspecifiedSecret
-#         = tsk.keys_valid().signing_capable().nth(0).unwrap().2.clone().into();
+#         = tsk.keys_valid().signing_capable().nth(0).unwrap().2.clone().try_into()?;
 #     let keypair = key.into_keypair()?;
 #
 #     // Start streaming an OpenPGP message.
@@ -155,6 +156,7 @@ create it:
 
 ```rust
 # use std::io::{self, Write};
+# use std::convert::TryInto;
 #
 # extern crate failure;
 # extern crate sequoia_openpgp as openpgp;
@@ -196,7 +198,7 @@ fn generate() -> openpgp::Result<openpgp::TPK> {
 #            -> openpgp::Result<()> {
 #     // Get the keypair to do the signing from the TPK.
 #     let key : key::UnspecifiedSecret
-#         = tsk.keys_valid().signing_capable().nth(0).unwrap().2.clone().into();
+#         = tsk.keys_valid().signing_capable().nth(0).unwrap().2.clone().try_into()?;
 #     let keypair = key.into_keypair()?;
 #
 #     // Start streaming an OpenPGP message.
@@ -300,6 +302,7 @@ implements [`io::Write`], and we simply write the plaintext to it.
 
 ```rust
 # use std::io::{self, Write};
+# use std::convert::TryInto;
 #
 # extern crate failure;
 # extern crate sequoia_openpgp as openpgp;
@@ -341,7 +344,7 @@ fn sign(sink: &mut Write, plaintext: &str, tsk: &openpgp::TPK)
            -> openpgp::Result<()> {
     // Get the keypair to do the signing from the TPK.
     let key : key::UnspecifiedSecret
-        = tsk.keys_valid().signing_capable().nth(0).unwrap().2.clone().into();
+        = tsk.keys_valid().signing_capable().nth(0).unwrap().2.clone().try_into()?;
     let keypair = key.into_keypair()?;
 
     // Start streaming an OpenPGP message.
@@ -456,7 +459,8 @@ Verified data can be read from this using [`io::Read`].
 
 ```rust
 # use std::io::{self, Write};
-# 
+# use std::convert::TryInto;
+#
 # extern crate failure;
 # extern crate sequoia_openpgp as openpgp;
 # use openpgp::serialize::stream::*;
@@ -497,7 +501,7 @@ Verified data can be read from this using [`io::Read`].
 #            -> openpgp::Result<()> {
 #     // Get the keypair to do the signing from the TPK.
 #     let key : key::UnspecifiedSecret
-#         = tsk.keys_valid().signing_capable().nth(0).unwrap().2.clone().into();
+#         = tsk.keys_valid().signing_capable().nth(0).unwrap().2.clone().try_into()?;
 #     let keypair = key.into_keypair()?;
 # 
 #     // Start streaming an OpenPGP message.
diff --git a/guide/src/chapter_02.md b/guide/src/chapter_02.md
index acc2cb2e..d2d11964 100644
--- a/guide/src/chapter_02.md
+++ b/guide/src/chapter_02.md
@@ -132,7 +132,7 @@ fn main() {
 #             .unwrap();
 #
 #         // The secret key is not encrypted.
-#         let mut pair = key.mark_parts_secret().into_keypair().unwrap();
+#         let mut pair = key.mark_parts_secret().unwrap().into_keypair().unwrap();
 #
 #         pkesks[0].decrypt(&mut pair)
 #             .and_then(|(algo, session_key)| decrypt(algo, &session_key))
@@ -275,7 +275,7 @@ fn generate() -> openpgp::Result<openpgp::TPK> {
 #             .unwrap();
 #
 #         // The secret key is not encrypted.
-#         let mut pair = key.mark_parts_secret().into_keypair().unwrap();
+#         let mut pair = key.mark_parts_secret().unwrap().into_keypair().unwrap();
 #
 #         pkesks[0].decrypt(&mut pair)
 #             .and_then(|(algo, session_key)| decrypt(algo, &session_key))
@@ -418,7 +418,7 @@ fn encrypt(sink: &mut Write, plaintext: &str, recipient: &openpgp::TPK)
 #             .unwrap();
 #
 #         // The secret key is not encrypted.
-#         let mut pair = key.mark_parts_secret().into_keypair().unwrap();
+#         let mut pair = key.mark_parts_secret().unwrap().into_keypair().unwrap();
 #
 #         pkesks[0].decrypt(&mut pair)
 #             .and_then(|(algo, session_key)| decrypt(algo, &session_key))
@@ -575,7 +575,7 @@ impl<'a> DecryptionHelper for Helper<'a> {
             .unwrap();
 
         // The secret key is not encrypted.
-        let mut pair = key.mark_parts_secret().into_keypair().unwrap();
+        let mut pair = key.mark_parts_secret().unwrap().into_keypair().unwrap();
 
         pkesks[0].decrypt(&mut pair)
             .and_then(|(algo, session_key)| decrypt(algo, &session_key))