Add Output implementation for deserializing JSON

Cargo.toml

@@ -11,11 +11,17 @@ keywords = ["child", "child-process", "command", "process", "shell"]
 categories = ["filesystem", "os"]
 exclude = ["/.github"]
 
+[features]
+serde = ["dep:serde", "dep:serde_json"]
+test_executables = ["nix", "serde"]
+
 [workspace]
 members = [".", "context-integration-tests", "memory-tests"]
 
 [dependencies]
 rustversion = "1.0.4"
+serde = { version = "1.0.196", optional = true }
+serde_json = {version = "1.0.113", optional = true }
 
 [dev-dependencies]
 executable-path = "1.0.0"
@@ -31,7 +37,7 @@ bitflags = "=1.2.1"
 [[bin]]
 name = "test_executables_helper"
 path = "src/test_executables/helper.rs"
-required-features = ["test_executables"]
+required-features = ["test_executables", "serde"]
 
 [[bin]]
 name = "test_executables_panic"
@@ -41,6 +47,3 @@ required-features = ["test_executables"]
 [target.'cfg(unix)'.dependencies.nix]
 version = "0.22.2"
 optional = true
-
-[features]
-test_executables = ["nix"]

context-integration-tests/Cargo.toml

@@ -5,6 +5,6 @@ edition = "2018"
 publish = false
 
 [target.'cfg(unix)'.dependencies]
-cradle = { path = ".." }
+cradle = { path = "..", features = ["serde"] }
 executable-path = "1.0.0"
 gag = "0.1.10"

justfile

@@ -50,3 +50,6 @@ all-rustc-versions *args="ci":
     cargo version
     just {{ args }}
   done
+
+watch +args='test':
+  cargo watch --clear --exec '{{args}}'

memory-tests/Cargo.toml

@@ -6,5 +6,5 @@ publish = false
 
 [dependencies]
 anyhow = "1.0.42"
-cradle = { path = ".." }
+cradle = { path = "..", features = ["serde"] }
 rustversion = "1.0.5"

src/common_re_exports.rs.snippet

@@ -6,5 +6,5 @@
 pub use crate::{
     error::Error,
     input::{CurrentDir, Env, Input, LogCommand, Split, Stdin},
-    output::{Output, Status, Stderr, StdoutTrimmed, StdoutUntrimmed},
+    output::{Output, Status, Stderr, StdoutTrimmed, StdoutUntrimmed, Json},
 };

src/error.rs

@@ -24,6 +24,9 @@ pub enum Error {
     /// }
     /// ```
     NoExecutableGiven,
+    Deserialize {
+        source: serde_json::Error,
+    },
     /// A `file not found` error occurred while trying to spawn
     /// the child process:
     ///
@@ -58,7 +61,10 @@ pub enum Error {
     /// - reading from `stdout` or `stderr` of the child process fails,
     /// - writing to the parent's `stdout` or `stderr` fails,
     /// - the given executable doesn't have the executable flag set.
-    CommandIoError { message: String, source: io::Error },
+    CommandIoError {
+        message: String,
+        source: io::Error,
+    },
     /// The child process exited with a non-zero exit code.
     ///
     /// ```
@@ -176,6 +182,7 @@ impl Display for Error {
         use Error::*;
         match self {
             NoExecutableGiven => write!(f, "no arguments given"),
+            Deserialize { source } => write!(f, "JSON deserialization failed: {source}"),
             FileNotFound { executable, .. } => {
                 let executable = executable.to_string_lossy();
                 write!(f, "File not found error when executing '{}'", executable)?;
@@ -223,6 +230,7 @@ impl std::error::Error for Error {
         use Error::*;
         match self {
             FileNotFound { source, .. } | CommandIoError { source, .. } => Some(source),
+            Deserialize { source } => Some(source),
             InvalidUtf8ToStdout { source, .. } | InvalidUtf8ToStderr { source, .. } => Some(source),
             NoExecutableGiven | NonZeroExitCode { .. } | Internal { .. } => None,
         }

src/lib.rs

@@ -1494,4 +1494,20 @@ mod tests {
             }
         }
     }
+
+    #[cfg(feature = "serde")]
+    mod json {
+        use super::*;
+
+        #[test]
+        fn json_can_be_deserialized() {
+            let Json(bar): Json<u32> = run_output!("echo", "100");
+            assert_eq!(bar, 100);
+        }
+
+        #[test]
+        fn json_errors() {
+            let result: Result<Json<u32>, Error> = run_result!("echo", "null");
+        }
+    }
 }

src/output.rs

@@ -1,7 +1,10 @@
 //! The [`Output`] trait that defines all possible outputs of a child process.
 
-use crate::{child_output::ChildOutput, config::Config, error::Error};
-use std::process::ExitStatus;
+use {
+    crate::{child_output::ChildOutput, config::Config, error::Error},
+    serde::de::DeserializeOwned,
+    std::process::ExitStatus,
+};
 
 /// All possible return types of [`run!`], [`run_output!`] or
 /// [`run_result!`] must implement this trait.
@@ -177,6 +180,24 @@ impl Output for StdoutTrimmed {
     }
 }
 
+#[derive(Debug)]
+pub struct Json<T: DeserializeOwned>(pub T);
+
+impl<T: DeserializeOwned> Output for Json<T> {
+    #[doc(hidden)]
+    fn configure(config: &mut Config) {
+        StdoutUntrimmed::configure(config);
+    }
+
+    #[doc(hidden)]
+    fn from_child_output(config: &Config, child_output: &ChildOutput) -> Result<Self, Error> {
+        let StdoutUntrimmed(stdout) = StdoutUntrimmed::from_child_output(config, child_output)?;
+        Ok(Self(
+            serde_json::from_str::<T>(&stdout).map_err(|source| Error::Deserialize { source })?,
+        ))
+    }
+}
+
 /// Same as [`StdoutTrimmed`], but does not trim whitespace from the output:
 ///
 /// ```