Add structured support to kv::Value using sval

.travis.yml

@@ -1,27 +1,31 @@
 language: rust
 sudo: false
 rust:
-  - 1.16.0
   - stable
   - beta
   - nightly
 matrix:
   include:
-    - rust: 1.21.0
-      script:
-        - cargo test --verbose --features kv_unstable
-        - cargo test --verbose --features "kv_unstable std"
     - rust: stable
+      env:
+        - LABEL="Embedded"
       script:
         - rustup target add thumbv6m-none-eabi
         - cargo build --verbose --target=thumbv6m-none-eabi
+    - rust: 1.16.0
+      env:
+        - LABEL="MSRV"
+      script:
+        - cargo build --verbose
+        - cargo build --verbose --features serde
+        - cargo build --verbose --features std
 script:
-  - cargo build --verbose
-  - cargo build --verbose --features serde
-  - cargo build --verbose --features std
   - cargo test --verbose
   - cargo test --verbose --features serde
   - cargo test --verbose --features std
+  - cargo test --verbose --features kv_unstable
+  - cargo test --verbose --features "kv_unstable std"
+  - cargo test --verbose --features "kv_unstable_sval"
   - cargo run --verbose --manifest-path test_max_level_features/Cargo.toml
   - cargo run --verbose --manifest-path test_max_level_features/Cargo.toml --release
 

Cargo.toml

@@ -16,7 +16,7 @@ exclude = ["rfcs/**/*", "/.travis.yml", "/appveyor.yml"]
 build = "build.rs"
 
 [package.metadata.docs.rs]
-features = ["std", "serde", "kv_unstable"]
+features = ["std", "serde", "kv_unstable_sval"]
 
 [[test]]
 name = "filters"
@@ -39,8 +39,10 @@ release_max_level_trace = []
 
 std = []
 
-# requires Rust `>= 1.21.0`
+# requires the latest stable
+# this will have a tighter MSRV before stabilization
 kv_unstable = []
+kv_unstable_sval = ["kv_unstable", "sval/fmt"]
 
 [badges]
 travis-ci = { repository = "rust-lang-nursery/log" }
@@ -49,6 +51,8 @@ appveyor = { repository = "alexcrichton/log" }
 [dependencies]
 cfg-if = "0.1.2"
 serde = { version = "1.0", optional = true, default-features = false }
+sval = { version = "0.4.2", optional = true, default-features = false }
 
 [dev-dependencies]
 serde_test = "1.0"
+sval = { version = "0.4.2", features = ["test"] }

src/kv/error.rs

@@ -1,6 +1,4 @@
 use std::fmt;
-#[cfg(feature = "std")]
-use std::io;
 
 /// An error encountered while working with structured data.
 #[derive(Debug)]
@@ -11,13 +9,13 @@ pub struct Error {
 #[derive(Debug)]
 enum Inner {
     #[cfg(feature = "std")]
-    Io(io::Error),
+    Boxed(std_support::BoxedError),
     Msg(&'static str),
     Fmt,
 }
 
 impl Error {
-    /// Create an error from the given message.
+    /// Create an error from a message.
     pub fn msg(msg: &'static str) -> Self {
         Error {
             inner: Inner::Msg(msg),
@@ -30,7 +28,7 @@ impl fmt::Display for Error {
         use self::Inner::*;
         match &self.inner {
             #[cfg(feature = "std")]
-            &Io(ref err) => err.fmt(f),
+            &Boxed(ref err) => err.fmt(f),
             &Msg(ref msg) => msg.fmt(f),
             &Fmt => fmt::Error.fmt(f),
         }
@@ -56,6 +54,20 @@ mod std_support {
     use super::*;
     use std::{error, io};
 
+    pub(super) type BoxedError = Box<error::Error + Send + Sync>;
+
+    impl Error {
+        /// Create an error from a standard error type.
+        pub fn boxed<E>(err: E) -> Self
+        where
+            E: Into<BoxedError>,
+        {
+            Error {
+                inner: Inner::Boxed(err.into())
+            }
+        }
+    }
+
     impl error::Error for Error {
         fn description(&self) -> &str {
             "key values error"
@@ -64,19 +76,13 @@ mod std_support {
 
     impl From<io::Error> for Error {
         fn from(err: io::Error) -> Self {
-            Error {
-                inner: Inner::Io(err)
-            }
+            Error::boxed(err)
         }
     }
 
     impl From<Error> for io::Error {
         fn from(err: Error) -> Self {
-            if let Inner::Io(err) = err.inner {
-                err
-            } else {
-                io::Error::new(io::ErrorKind::Other, err)
-            }
+            io::Error::new(io::ErrorKind::Other, err)
         }
     }
 }

src/kv/value/impls.rs

@@ -241,16 +241,16 @@ mod tests {
 
     #[test]
     fn test_to_value_display() {
-        assert_eq!(42u64.to_value().to_str_buf(), "42");
-        assert_eq!(42i64.to_value().to_str_buf(), "42");
-        assert_eq!(42.01f64.to_value().to_str_buf(), "42.01");
-        assert_eq!(true.to_value().to_str_buf(), "true");
-        assert_eq!('a'.to_value().to_str_buf(), "'a'");
-        assert_eq!(format_args!("a {}", "value").to_value().to_str_buf(), "a value");
-        assert_eq!("a loong string".to_value().to_str_buf(), "\"a loong string\"");
-        assert_eq!(Some(true).to_value().to_str_buf(), "true");
-        assert_eq!(().to_value().to_str_buf(), "None");
-        assert_eq!(Option::None::<bool>.to_value().to_str_buf(), "None");
+        assert_eq!(42u64.to_value().to_string(), "42");
+        assert_eq!(42i64.to_value().to_string(), "42");
+        assert_eq!(42.01f64.to_value().to_string(), "42.01");
+        assert_eq!(true.to_value().to_string(), "true");
+        assert_eq!('a'.to_value().to_string(), "'a'");
+        assert_eq!(format_args!("a {}", "value").to_value().to_string(), "a value");
+        assert_eq!("a loong string".to_value().to_string(), "\"a loong string\"");
+        assert_eq!(Some(true).to_value().to_string(), "true");
+        assert_eq!(().to_value().to_string(), "None");
+        assert_eq!(Option::None::<bool>.to_value().to_string(), "None");
     }
 
     #[test]