Work around compiler bug

This tweaks the Agora context type we use in order to avoid a recurring
Rust compiler bug (rust-lang/rust#71723) which
makes it suddenly impossible to carry the context across an await. This
comes at the cost of increasing String allocations. Though the use of
snmalloc mitigates this cost somewhat.

Author: Theodus

graph-gateway/src/block_constraints.rs

@@ -42,9 +42,9 @@ pub fn block_constraints<'c>(context: &'c Context<'c>) -> Option<BTreeSet<BlockC
                 let defaults = query
                     .variable_definitions
                     .iter()
-                    .filter(|d| !vars.0.contains_key(d.name))
-                    .filter_map(|d| Some((d.name, d.default_value.as_ref()?.to_graphql())))
-                    .collect::<BTreeMap<&str, StaticValue>>();
+                    .filter(|d| !vars.0.contains_key(&d.name))
+                    .filter_map(|d| Some((d.name.clone(), d.default_value.as_ref()?.to_graphql())))
+                    .collect::<BTreeMap<String, StaticValue>>();
                 (&query.selection_set, defaults)
             }
             OperationDefinition::Query(_)
@@ -88,9 +88,9 @@ pub fn make_query_deterministic(
                 let defaults = query
                     .variable_definitions
                     .iter()
-                    .filter(|d| !vars.0.contains_key(d.name))
-                    .filter_map(|d| Some((d.name, d.default_value.as_ref()?.to_graphql())))
-                    .collect::<BTreeMap<&str, StaticValue>>();
+                    .filter(|d| !vars.0.contains_key(&d.name))
+                    .filter_map(|d| Some((d.name.clone(), d.default_value.as_ref()?.to_graphql())))
+                    .collect::<BTreeMap<String, StaticValue>>();
                 (&mut query.selection_set, defaults)
             }
             OperationDefinition::Query(_)
@@ -123,7 +123,7 @@ pub fn make_query_deterministic(
                 None => {
                     selection_field
                         .arguments
-                        .push(("block", deterministic_block(&latest.hash)));
+                        .push(("block".to_string(), deterministic_block(&latest.hash)));
                 }
             };
         }
@@ -146,21 +146,21 @@ pub fn make_query_deterministic(
     .ok()
 }
 
-fn deterministic_block<'c>(hash: &Bytes32) -> Value<'c, &'c str> {
+fn deterministic_block<'c>(hash: &Bytes32) -> Value<'c, String> {
     Value::Object(BTreeMap::from_iter([(
-        "hash",
+        "hash".to_string(),
         Value::String(hash.to_string()),
     )]))
 }
 
-fn field_constraint<'c>(
+fn field_constraint(
     vars: &QueryVariables,
-    defaults: &BTreeMap<&str, StaticValue>,
-    field: &Value<'c, &'c str>,
+    defaults: &BTreeMap<String, StaticValue>,
+    field: &Value<'_, String>,
 ) -> Option<BlockConstraint> {
     match field {
         Value::Object(fields) => parse_constraint(vars, defaults, fields),
-        Value::Variable(name) => match vars.get(*name)? {
+        Value::Variable(name) => match vars.get(name)? {
             Value::Object(fields) => parse_constraint(vars, defaults, fields),
             _ => None,
         },
@@ -170,7 +170,7 @@ fn field_constraint<'c>(
 
 fn parse_constraint<'c, T: Text<'c>>(
     vars: &QueryVariables,
-    defaults: &BTreeMap<&str, StaticValue>,
+    defaults: &BTreeMap<String, StaticValue>,
     fields: &BTreeMap<T::Value, Value<'c, T>>,
 ) -> Option<BlockConstraint> {
     let field = fields.iter().at_most_one().ok()?;
@@ -190,7 +190,7 @@ fn parse_constraint<'c, T: Text<'c>>(
 fn parse_hash<'c, T: Text<'c>>(
     hash: &Value<'c, T>,
     variables: &QueryVariables,
-    defaults: &BTreeMap<&str, StaticValue>,
+    defaults: &BTreeMap<String, StaticValue>,
 ) -> Option<Bytes32> {
     match hash {
         Value::String(hash) => hash.parse().ok(),
@@ -208,7 +208,7 @@ fn parse_hash<'c, T: Text<'c>>(
 fn parse_number<'c, T: Text<'c>>(
     number: &Value<'c, T>,
     variables: &QueryVariables,
-    defaults: &BTreeMap<&str, StaticValue>,
+    defaults: &BTreeMap<String, StaticValue>,
 ) -> Option<u64> {
     let n = match number {
         Value::Int(n) => n,

graph-gateway/src/client_query.rs

@@ -732,6 +732,6 @@ fn count_top_level_selection_sets(ctx: &AgoraContext) -> anyhow::Result<usize> {
             OperationDefinition::Mutation(_) => bail!("Mutations not yet supported"),
             OperationDefinition::Subscription(_) => bail!("Subscriptions not yet supported"),
         })
-        .collect::<anyhow::Result<Vec<&SelectionSet<&str>>>>()?;
+        .collect::<anyhow::Result<Vec<&SelectionSet<String>>>>()?;
     Ok(selection_sets.into_iter().map(|set| set.items.len()).sum())
 }

indexer-selection/src/lib.rs

@@ -38,7 +38,9 @@ use std::{
     sync::Arc,
 };
 
-pub type Context<'c> = cost_model::Context<'c, &'c str>;
+// We have to use `String` instead of `&'c str` here because of compiler bug triggered when holding
+// a context across an await. See https://github.com/rust-lang/rust/issues/71723
+pub type Context<'c> = cost_model::Context<'c, String>;
 
 #[derive(Clone, Debug)]
 pub struct Selection {