Switch from failure to anyhow.

  - Use the anyhow crate instead of failure to implement the dynamic
    side of our error handling.  anyhow::Error derefs to dyn
    std::error::Error, allowing better interoperability with other
    stdlib-based error handling libraries.

  - Fixes #444.

71 files changed, 237 insertions, 336 deletions

diff --git a/Cargo.lock b/Cargo.lock
index aaab7a5d..5d3f2643 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -22,6 +22,11 @@ dependencies = [
 ]
 
 [[package]]
+name = "anyhow"
+version = "1.0.26"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
+[[package]]
 name = "arrayref"
 version = "0.3.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -1559,8 +1564,8 @@ dependencies = [
 name = "sequoia-core"
 version = "0.15.0"
 dependencies = [
+ "anyhow 1.0.26 (registry+https://github.com/rust-lang/crates.io-index)",
  "dirs 2.0.2 (registry+https://github.com/rust-lang/crates.io-index)",
- "failure 0.1.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "tempfile 3.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "thiserror 1.0.11 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
@@ -1569,7 +1574,7 @@ dependencies = [
 name = "sequoia-ffi"
 version = "0.15.0"
 dependencies = [
- "failure 0.1.6 (registry+https://github.com/rust-lang/crates.io-index)",
+ "anyhow 1.0.26 (registry+https://github.com/rust-lang/crates.io-index)",
  "filetime 0.2.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "lazy_static 1.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "libc 0.2.67 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1598,7 +1603,7 @@ dependencies = [
 name = "sequoia-guide"
 version = "0.15.0"
 dependencies = [
- "failure 0.1.6 (registry+https://github.com/rust-lang/crates.io-index)",
+ "anyhow 1.0.26 (registry+https://github.com/rust-lang/crates.io-index)",
  "sequoia-openpgp 0.15.0",
 ]
 
@@ -1606,9 +1611,9 @@ dependencies = [
 name = "sequoia-ipc"
 version = "0.15.0"
 dependencies = [
+ "anyhow 1.0.26 (registry+https://github.com/rust-lang/crates.io-index)",
  "capnp-rpc 0.10.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "clap 2.33.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "failure 0.1.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "fs2 0.4.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "futures 0.1.29 (registry+https://github.com/rust-lang/crates.io-index)",
  "lalrpop 0.17.2 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1629,7 +1634,7 @@ dependencies = [
 name = "sequoia-net"
 version = "0.15.0"
 dependencies = [
- "failure 0.1.6 (registry+https://github.com/rust-lang/crates.io-index)",
+ "anyhow 1.0.26 (registry+https://github.com/rust-lang/crates.io-index)",
  "futures 0.1.29 (registry+https://github.com/rust-lang/crates.io-index)",
  "http 0.1.21 (registry+https://github.com/rust-lang/crates.io-index)",
  "hyper 0.12.35 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1652,10 +1657,10 @@ dependencies = [
 name = "sequoia-openpgp"
 version = "0.15.0"
 dependencies = [
+ "anyhow 1.0.26 (registry+https://github.com/rust-lang/crates.io-index)",
  "base64 0.11.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "buffered-reader 0.14.0",
  "bzip2 0.3.3 (registry+https://github.com/rust-lang/crates.io-index)",
- "failure 0.1.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "flate2 1.0.13 (registry+https://github.com/rust-lang/crates.io-index)",
  "idna 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "lalrpop 0.17.2 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1675,7 +1680,7 @@ dependencies = [
 name = "sequoia-openpgp-ffi"
 version = "0.15.0"
 dependencies = [
- "failure 0.1.6 (registry+https://github.com/rust-lang/crates.io-index)",
+ "anyhow 1.0.26 (registry+https://github.com/rust-lang/crates.io-index)",
  "filetime 0.2.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "lazy_static 1.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "libc 0.2.67 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1688,11 +1693,11 @@ dependencies = [
 name = "sequoia-sqv"
 version = "0.15.0"
 dependencies = [
+ "anyhow 1.0.26 (registry+https://github.com/rust-lang/crates.io-index)",
  "assert_cli 0.6.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "chrono 0.4.10 (registry+https://github.com/rust-lang/crates.io-index)",
  "clap 2.33.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "colored 1.9.1 (registry+https://github.com/rust-lang/crates.io-index)",
- "failure 0.1.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "sequoia-openpgp 0.15.0",
 ]
 
@@ -1700,10 +1705,10 @@ dependencies = [
 name = "sequoia-store"
 version = "0.15.0"
 dependencies = [
+ "anyhow 1.0.26 (registry+https://github.com/rust-lang/crates.io-index)",
  "capnp 0.10.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "capnp-rpc 0.10.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "capnpc 0.10.2 (registry+https://github.com/rust-lang/crates.io-index)",
- "failure 0.1.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "futures 0.1.29 (registry+https://github.com/rust-lang/crates.io-index)",
  "rand 0.7.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "rusqlite 0.19.0 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1720,12 +1725,12 @@ dependencies = [
 name = "sequoia-tool"
 version = "0.15.0"
 dependencies = [
+ "anyhow 1.0.26 (registry+https://github.com/rust-lang/crates.io-index)",
  "assert_cli 0.6.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "chrono 0.4.10 (registry+https://github.com/rust-lang/crates.io-index)",
  "clap 2.33.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "colored 1.9.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "crossterm 0.13.3 (registry+https://github.com/rust-lang/crates.io-index)",
- "failure 0.1.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "itertools 0.8.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "prettytable-rs 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "rpassword 4.0.3 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -2262,6 +2267,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum adler32 1.0.4 (registry+https://github.com/rust-lang/crates.io-index)" = "5d2e7343e7fc9de883d1b0341e0b13970f764c14101234857d2ddafa1cb1cac2"
 "checksum aho-corasick 0.7.9 (registry+https://github.com/rust-lang/crates.io-index)" = "d5e63fd144e18ba274ae7095c0197a870a7b9468abc801dd62f190d80817d2ec"
 "checksum ansi_term 0.11.0 (registry+https://github.com/rust-lang/crates.io-index)" = "ee49baf6cb617b853aa8d93bf420db2383fab46d314482ca2803b40d5fde979b"
+"checksum anyhow 1.0.26 (registry+https://github.com/rust-lang/crates.io-index)" = "7825f6833612eb2414095684fcf6c635becf3ce97fe48cf6421321e93bfbd53c"
 "checksum arrayref 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)" = "a4c527152e37cf757a3f78aae5a06fbeefdb07ccc535c980a3208ee3060dd544"
 "checksum arrayvec 0.5.1 (registry+https://github.com/rust-lang/crates.io-index)" = "cff77d8686867eceff3105329d4698d96c2391c176d5d03adc90c7389162b5b8"
 "checksum ascii-canvas 2.0.0 (registry+https://github.com/rust-lang/crates.io-index)" = "ff8eb72df928aafb99fe5d37b383f2fe25bd2a765e3e5f7c365916b6f2463a29"
diff --git a/core/Cargo.toml b/core/Cargo.toml
index d6a95c53..f3f013f8 100644
--- a/core/Cargo.toml
+++ b/core/Cargo.toml
@@ -21,7 +21,7 @@ gitlab = { repository = "sequoia-pgp/sequoia" }
 maintenance = { status = "actively-developed" }
 
 [dependencies]
+anyhow = "1"
 dirs = "2.0"
-failure = "0.1.2"
 tempfile = "3.1"
 thiserror = "1"
diff --git a/core/src/lib.rs b/core/src/lib.rs
index aa6ba30d..5db7e6bf 100644
--- a/core/src/lib.rs
+++ b/core/src/lib.rs
@@ -20,8 +20,6 @@
 
 extern crate dirs;
 extern crate tempfile;
-#[macro_use]
-extern crate failure;
 
 use std::fmt;
 use std::io;
@@ -199,7 +197,7 @@ impl Config {
             if home_not_set {
                 c.home =
                     dirs::home_dir().ok_or(
-                        format_err!("Failed to get users home directory"))?
+                        anyhow::anyhow!("Failed to get users home directory"))?
                 .join(".sequoia");
             }
         }
@@ -266,7 +264,7 @@ impl Config {
 /* Error handling.  */
 
 /// Result type for Sequoia.
-pub type Result<T> = ::std::result::Result<T, failure::Error>;
+pub type Result<T> = ::std::result::Result<T, anyhow::Error>;
 
 #[derive(thiserror::Error, Debug)]
 /// Errors for Sequoia.
diff --git a/ffi-macros/src/lib.rs b/ffi-macros/src/lib.rs
index e4107c49..8b315b72 100644
--- a/ffi-macros/src/lib.rs
+++ b/ffi-macros/src/lib.rs
@@ -648,7 +648,7 @@ fn derive_conversion_functions(mut st: syn::ItemStruct,
         }
 
         impl #generics crate::MoveResultIntoRaw<Option<::std::ptr::NonNull<#wrapper #generics>>>
-            for ::failure::Fallible<#wrapped>
+            for ::anyhow::Result<#wrapped>
         {
             fn move_into_raw(self, errp: Option<&mut *mut crate::error::Error>)