graphql_client: impl Display for GraphQLError

This formats the error as a compiler-like output line.

Author: mathstuf

Cargo.toml

@@ -11,6 +11,7 @@ categories = ["network-programming", "web-programming", "wasm"]
 [dependencies]
 failure = "0.1"
 graphql_query_derive = {path = "./graphql_query_derive", version = "0.4.0"}
+itertools = "0.7"
 serde = "1.0"
 serde_derive = "1.0"
 serde_json = "1.0"

src/lib.rs

@@ -5,6 +5,7 @@
 #![deny(warnings)]
 #![deny(missing_docs)]
 
+extern crate itertools;
 extern crate serde;
 #[macro_use]
 extern crate serde_derive;
@@ -17,6 +18,9 @@ extern crate serde_json;
 pub use graphql_query_derive::*;
 
 use std::collections::HashMap;
+use std::fmt::{self, Display};
+
+use itertools::Itertools;
 
 /// A convenience trait that can be used to build a GraphQL request body.
 ///
@@ -109,6 +113,15 @@ pub enum PathFragment {
     Index(i32),
 }
 
+impl Display for PathFragment {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match *self {
+            PathFragment::Key(ref key) => write!(f, "{}", key),
+            PathFragment::Index(ref idx) => write!(f, "{}", idx),
+        }
+    }
+}
+
 /// An element in the top-level `errors` array of a response body.
 ///
 /// This tries to be as close to the spec as possible.
@@ -189,6 +202,25 @@ pub struct Error {
     pub extensions: Option<HashMap<String, serde_json::Value>>,
 }
 
+impl Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        // Use `/` as a separator like JSON Pointer.
+        let path = self.path
+            .as_ref()
+            .map(|fragments| format!("{}", fragments.iter().format("/")))
+            .unwrap_or_else(|| "<query>".to_string());
+
+        // Get the location of the error. We'll use just the first location for this.
+        let loc = self.locations
+            .as_ref()
+            .and_then(|locations| locations.iter().next())
+            .cloned()
+            .unwrap_or_else(Location::default);
+
+        write!(f, "{}:{}:{}: {}", path, loc.line, loc.column, self.message)
+    }
+}
+
 /// The generic shape taken by the responses of GraphQL APIs.
 ///
 /// This will generally be used with the `ResponseData` struct from a derived module.