Add containsSupergraphSpec (#44)

This method is meant to quickly check if
`transformSupergraphToPublicSchema` is needed.
Obviously, in most cases when `transformSupergraphToPublicSchema` is
used, a provided schema contains Supergraph spec (join__Graph etc).

Why do I create it then?
We have a special case in GraphQL Hive where we persist the output of
`transformSupergraphToPublicSchema`, but when Apollo Federation adds
something new, we might want to run this method again to remove new
pieces.

#### Performance

I used a Supergraph SDL with ~20k LOC and create three copies.
First copy used `field(whatever: join__Graph)` as an argument somewhere
in the middle.
Second copy had `scalar join__DirectiveArguments`, also in the middle of
the file.
Third copy had `directive @join__directive` definition (yeah yeah, in
the middle).

I wrote three versions of `containsSupergraphSpec` to make sure it has
minimal performance footprint.

1. for-loop over all federation scalars, enums and directives that used
`sdl.includes("[name") or sdl.includes(" name")`
2. same for-loop but directives where checked first
3. regex (current implementation).

I ran it 1000 times and I got (average):
1. 1.56 ms
2. 0.83 ms
3. 0.59 ms

.changeset/tricky-badgers-punch.md

@@ -0,0 +1,5 @@
+---
+'@theguild/federation-composition': patch
+---
+
+Add containsSupergraphSpec to detect if Supergraph related scalars, enums or directives are used

src/graphql/contains-supergraph-spec.ts

@@ -0,0 +1,17 @@
+import { federationDirectives, federationEnums, federationScalars } from "./transform-supergraph-to-public-schema.js";
+
+
+const supergraphSpecDetectionRegex = new RegExp(
+    Array.from(federationScalars)
+      .concat(Array.from(federationEnums))
+      // "[NAME" or " NAME" for scalars and enums
+      .map(name => [`\\[${name}`, `\\s${name}`])
+      .flat(2)
+      // "@NAME" for directives
+      .concat(Array.from(federationDirectives).map(name => `@${name}`))
+      .join('|'),
+  );
+
+  export function containsSupergraphSpec(sdl: string): boolean {
+    return supergraphSpecDetectionRegex.test(sdl);
+  }

src/graphql/transform-supergraph-to-public-schema.ts

@@ -9,15 +9,21 @@ import {
   type SchemaDefinitionNode,
 } from 'graphql';
 
-const federationScalars = new Set(['_FieldSet', 'link__Import', 'join__FieldSet']);
-const federationEnums = new Set(['core__Purpose', 'join__Graph', 'link__Purpose']);
-const federationDirectives = new Set([
+export const federationScalars = new Set([
+  '_FieldSet',
+  'link__Import',
+  'join__FieldSet',
+  'join__DirectiveArguments',
+]);
+export const federationEnums = new Set(['core__Purpose', 'join__Graph', 'link__Purpose']);
+export const federationDirectives = new Set([
   'link',
   'tag',
   'join__graph',
   'join__type',
   'join__implements',
   'join__unionMember',
+  'join__directive',
   'join__enumValue',
   'join__field',
   'inaccessible',

src/index.ts

@@ -2,4 +2,5 @@ export * from './compose.js';
 export * from './types.js';
 export * from './validate.js';
 export { transformSupergraphToPublicSchema } from './graphql/transform-supergraph-to-public-schema.js';
+export { containsSupergraphSpec } from './graphql/contains-supergraph-spec.js';
 export { sortSDL } from './graphql/sort-sdl.js';