Improve error messages when one of the required attributes is missing

In the derive crate.

Author: tomhoule

CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ## Unreleased
 
+### Added
+
+- Better error messages from the derive macro stwhen the schema or the query file path is not found.
+
 ## 0.5.0
 
 ### Added

graphql_query_derive/Cargo.toml

@@ -10,6 +10,7 @@ repository = "https://github.com/graphql-rust/graphql-client"
 proc-macro = true
 
 [dependencies]
+failure = "0.1"
 syn = "0.15"
 proc-macro2 = { version = "0.4", features = [] }
 graphql_client_codegen = { path = "../graphql_client_codegen/", version = "0.5.0" }

graphql_query_derive/src/lib.rs

@@ -1,7 +1,10 @@
+extern crate failure;
 extern crate graphql_client_codegen;
 extern crate proc_macro;
 extern crate proc_macro2;
 extern crate syn;
+
+use failure::ResultExt;
 use graphql_client_codegen::*;
 
 use proc_macro2::TokenStream;
@@ -22,10 +25,14 @@ fn build_query_and_schema_path(
     let cargo_manifest_dir =
         ::std::env::var("CARGO_MANIFEST_DIR").expect("CARGO_MANIFEST_DIR env variable is defined");
 
-    let query_path = attributes::extract_attr(input, "query_path").unwrap();
+    let query_path = attributes::extract_attr(input, "query_path")
+        .context("Extracting query path")
+        .unwrap();
     let query_path = format!("{}/{}", cargo_manifest_dir, query_path);
     let query_path = ::std::path::Path::new(&query_path).to_path_buf();
-    let schema_path = attributes::extract_attr(input, "schema_path").unwrap();
+    let schema_path = attributes::extract_attr(input, "schema_path")
+        .context("Extracting schema path")
+        .unwrap();
     let schema_path = ::std::path::Path::new(&cargo_manifest_dir).join(schema_path);
     (query_path, schema_path)
 }