docs(examples): add serde_json integration example (#407)

Cargo.toml

@@ -41,6 +41,7 @@ syn = { version = "2.0.48", features = ["full"] }
 regex = "1.10"
 lazy_static = "1.4"
 
+serde = { version = "1.0.196", features = ["derive"] }
 serde_json = "1.0.113"
 strip-ansi-escapes = "0.2.0"
 
@@ -70,3 +71,7 @@ members = ["miette-derive"]
 
 [package.metadata.docs.rs]
 all-features = true
+
+[[example]]
+name = "serde_json"
+required-features = ["fancy"]

examples/serde_json.rs

@@ -0,0 +1,48 @@
+//! This example shows how to integrate miette with serde_json
+//! so the decoding source will be annotated with the decoding error,
+//! providing contextual information about the error.
+
+use miette::{IntoDiagnostic, SourceOffset};
+use serde_json::{self, json};
+
+#[derive(Debug, serde::Deserialize)]
+struct Library {
+    #[allow(unused)]
+    name: String,
+}
+
+#[derive(Debug, thiserror::Error, miette::Diagnostic)]
+#[error("malformed json provided")]
+struct SerdeError {
+    cause: serde_json::Error,
+    #[source_code]
+    input: String,
+    #[label("{cause}")]
+    location: SourceOffset,
+}
+
+impl SerdeError {
+    /// Takes the input and the `serde_json::Error` and returns a SerdeError
+    /// that can be rendered nicely with miette.
+    pub fn from_serde_error(input: impl Into<String>, cause: serde_json::Error) -> Self {
+        let input = input.into();
+        let location = SourceOffset::from_location(&input, cause.line(), cause.column());
+        Self {
+            cause,
+            input,
+            location,
+        }
+    }
+}
+
+fn main() -> miette::Result<()> {
+    let input = serde_json::to_string_pretty(&json!({
+        "name": 123
+    }))
+    .into_diagnostic()?;
+
+    let _library: Library =
+        serde_json::from_str(&input).map_err(|cause| SerdeError::from_serde_error(input, cause))?;
+
+    Ok(())
+}