Add tracing support

docs/book/content/SUMMARY.md

@@ -25,6 +25,8 @@
     - [Hyper](servers/hyper.md)
   - [Third Party Integrations](servers/third-party.md)
 
+- [Tracing](tracing/index.md)
+
 - [Advanced Topics](advanced/index.md)
 
   - [Introspection](advanced/introspection.md)

docs/book/content/tracing/index.md

@@ -0,0 +1,38 @@
+# Tracing
+
+Juniper relies on the [tracing](https://crates.io/crates/tracing) crate for instrumentation.
+
+!FILENAME Cargo.toml
+
+```toml
+[dependencies]
+tracing = "0.1.17"
+tracing-subscriber = "0.2.9"
+tracing-log = "0.1.1"
+```
+
+## Usage
+
+```rust
+# extern crate tracing;
+# extern crate tracing_subscriber;
+# extern crate tracing_log;
+fn main() {
+    // compatibility with the log crate (unstable)
+    // converts all log records into tracing events
+    tracing_log::LogTracer::init().expect("LogTracer init failed");
+
+    // a builder for `FmtSubscriber`.
+    let subscriber = tracing_subscriber::FmtSubscriber::builder()
+        // all spans/events with a level higher than TRACE
+        // (e.g, debug, info, warn, etc.) will be written to stdout.
+        .with_max_level(tracing::Level::TRACE)
+        // completes the builder.
+        .finish();
+
+    tracing::subscriber::set_global_default(subscriber)
+        .expect("Setting default tracing subscriber failed");
+
+    // ...
+}
+```

docs/book/tests/Cargo.toml

@@ -20,6 +20,10 @@ skeptic = "0.13"
 serde_json = "1.0.39"
 uuid = "0.8"
 
+tracing = "0.1.17"
+tracing-subscriber = "0.2.9"
+tracing-log = "0.1.1"
+
 [build-dependencies]
 skeptic = "0.13"
 

juniper/Cargo.toml

@@ -52,6 +52,8 @@ url = { version = "2", optional = true }
 uuid = { version = "0.8", optional = true }
 graphql-parser = {version = "0.3.0", optional = true }
 
+tracing = {version = "0.1.17", optional = true }
+
 [dev-dependencies]
 bencher = "0.1.2"
 serde_json = { version = "1.0.2" }

juniper/src/lib.rs

@@ -260,7 +260,10 @@ where
         let errors = validate_input_values(variables, operation, &root_node.schema);
 
         if !errors.is_empty() {
-            return Err(GraphQLError::ValidationError(errors));
+            let gql_error = GraphQLError::ValidationError(errors);
+            __juniper_trace_error!("GraphQLError: {:?}", gql_error);
+
+            return Err(gql_error);
         }
     }
 
@@ -293,7 +296,10 @@ where
 
         let errors = ctx.into_errors();
         if !errors.is_empty() {
-            return Err(GraphQLError::ValidationError(errors));
+            let gql_error = GraphQLError::ValidationError(errors);
+            __juniper_trace_error!("GraphQLError: {:?}", gql_error);
+
+            return Err(gql_error);
         }
     }
 
@@ -303,7 +309,10 @@ where
         let errors = validate_input_values(variables, operation, &root_node.schema);
 
         if !errors.is_empty() {
-            return Err(GraphQLError::ValidationError(errors));
+            let gql_error = GraphQLError::ValidationError(errors);
+            __juniper_trace_error!("GraphQLError: {:?}", gql_error);
+
+            return Err(gql_error);
         }
     }
 
@@ -338,7 +347,10 @@ where
 
         let errors = ctx.into_errors();
         if !errors.is_empty() {
-            return Err(GraphQLError::ValidationError(errors));
+            let gql_error = GraphQLError::ValidationError(errors);
+            __juniper_trace_error!("GraphQLError: {:?}", gql_error);
+
+            return Err(gql_error);
         }
     }
 
@@ -348,7 +360,10 @@ where
         let errors = validate_input_values(&variables, operation, &root_node.schema);
 
         if !errors.is_empty() {
-            return Err(GraphQLError::ValidationError(errors));
+            let gql_error = GraphQLError::ValidationError(errors);
+            __juniper_trace_error!("GraphQLError: {:?}", gql_error);
+
+            return Err(gql_error);
         }
     }
 

juniper/src/macros/mod.rs

@@ -10,3 +10,5 @@ mod interface;
 mod tests;
 
 pub mod subscription_helpers;
+
+mod tracing;

juniper/src/macros/tracing.rs

@@ -0,0 +1,48 @@
+#[doc(hidden)]
+#[macro_export]
+macro_rules! __juniper_trace_internal {
+    ($trace_type:ident; $($element:expr),*) => {{
+        #[cfg(feature = "tracing")]
+        tracing::$trace_type!($($element),*);
+    }};
+}
+
+#[doc(hidden)]
+#[macro_export]
+macro_rules! __juniper_trace {
+    ($($element:expr),*) => {{
+        $crate::__juniper_trace_internal!(trace; $($element),*)
+    }};
+}
+
+#[doc(hidden)]
+#[macro_export]
+macro_rules! __juniper_trace_debug {
+    ($($element:expr),*) => {{
+        $crate::__juniper_trace_internal!(debug; $($element),*)
+    }};
+}
+
+#[doc(hidden)]
+#[macro_export]
+macro_rules! __juniper_trace_info {
+    ($($element:expr),*) => {{
+        $crate::__juniper_trace_internal!(info; $($element),*)
+    }};
+}
+
+#[doc(hidden)]
+#[macro_export]
+macro_rules! __juniper_trace_warn {
+    ($($element:expr),*) => {{
+        $crate::__juniper_trace_internal!(warn; $($element),*)
+    }};
+}
+
+#[doc(hidden)]
+#[macro_export]
+macro_rules! __juniper_trace_error {
+    ($($element:expr),*) => {{
+        $crate::__juniper_trace_internal!(error; $($element),*)
+    }};
+}