Add mnemonic to descriptors example.

This was initially requested by one user but might be
relevant for other users as well.

Cargo.toml

@@ -153,6 +153,11 @@ name = "esplora_backend_asynchronous"
 path = "examples/esplora_backend_asynchronous.rs"
 required-features = ["use-esplora-reqwest", "reqwest-default-tls", "async-interface"]
 
+[[example]]
+name = "mnemonic_to_descriptors"
+path = "examples/mnemonic_to_descriptors.rs"
+required-features = ["all-keys"]
+
 [workspace]
 members = ["macros"]
 [package.metadata.docs.rs]

examples/mnemonic_to_descriptors.rs

@@ -0,0 +1,60 @@
+// Copyright (c) 2020-2021 Bitcoin Dev Kit Developers
+//
+// This file is licensed under the Apache License, Version 2.0 <LICENSE-APACHE
+// or http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your option.
+// You may not use this file except in accordance with one or both of these
+// licenses.
+
+use bdk::bitcoin::secp256k1::Secp256k1;
+use bdk::bitcoin::util::bip32::DerivationPath;
+use bdk::bitcoin::Network;
+use bdk::descriptor;
+use bdk::descriptor::IntoWalletDescriptor;
+use bdk::keys::bip39::{Language, Mnemonic, WordCount};
+use bdk::keys::{GeneratableKey, GeneratedKey};
+use bdk::miniscript::Tap;
+use bdk::Error as BDK_Error;
+use std::error::Error;
+use std::str::FromStr;
+
+/// This example demonstrates how to generate a mnemonic phrase
+/// using BDK and use that to generate a descriptor string.
+fn main() -> Result<(), Box<dyn Error>> {
+    let secp = Secp256k1::new();
+
+    // In this example we are generating a 12 words mnemonic phrase
+    // but it is also possible generate 15, 18, 21 and 24 words
+    // using their respective `WordCount` variant.
+    let mnemonic: GeneratedKey<_, Tap> =
+        Mnemonic::generate((WordCount::Words12, Language::English))
+            .map_err(|_| BDK_Error::Generic("Mnemonic generation error".to_string()))?;
+
+    println!("Mnemonic phrase: {}", *mnemonic);
+    let mnemonic_with_passphrase = (mnemonic, None);
+
+    // define external and internal derivation key path
+    let external_path = DerivationPath::from_str("m/86h/0h/0h/0").unwrap();
+    let internal_path = DerivationPath::from_str("m/86h/0h/0h/1").unwrap();
+
+    // generate external and internal descriptor from mnemonic
+    let (external_descriptor, ext_keymap) =
+        descriptor!(tr((mnemonic_with_passphrase.clone(), external_path)))?
+            .into_wallet_descriptor(&secp, Network::Testnet)?;
+    let (internal_descriptor, int_keymap) =
+        descriptor!(tr((mnemonic_with_passphrase, internal_path)))?
+            .into_wallet_descriptor(&secp, Network::Testnet)?;
+
+    println!("tpub external descriptor: {}", external_descriptor);
+    println!("tpub internal descriptor: {}", internal_descriptor);
+    println!(
+        "tprv external descriptor: {}",
+        external_descriptor.to_string_with_secret(&ext_keymap)
+    );
+    println!(
+        "tprv internal descriptor: {}",
+        internal_descriptor.to_string_with_secret(&int_keymap)
+    );
+
+    Ok(())
+}