[IJ/AS Plugin] Add fragment usages when going to fragment declaration (#5189)

Author: BoD

intellij-plugin/src/main/kotlin/com/apollographql/ijplugin/navigation/GraphQLGotoDeclarationHandler.kt

@@ -69,6 +69,11 @@ class GraphQLGotoDeclarationHandler : GotoDeclarationHandler {
       val resolvedElement = sourceElement.parent?.reference?.resolve()
       if (resolvedElement != null) {
         add(resolvedElement)
+      } else {
+        // Special case for Fragment declaration: we switch to the Fragment's usages
+        if (gqlElement is GraphQLFragmentDefinition) {
+          addAll(findFragmentSpreads(gqlElement.project) { it.nameIdentifier.reference?.resolve() == gqlElement.nameIdentifier })
+        }
       }
 
       // Add Kotlin definition(s)

intellij-plugin/src/main/kotlin/com/apollographql/ijplugin/navigation/GraphQLNavigation.kt

@@ -17,6 +17,7 @@ import com.intellij.lang.jsgraphql.psi.GraphQLInlineFragment
 import com.intellij.lang.jsgraphql.psi.GraphQLInputObjectTypeDefinition
 import com.intellij.lang.jsgraphql.psi.GraphQLInputValueDefinition
 import com.intellij.lang.jsgraphql.psi.GraphQLOperationDefinition
+import com.intellij.lang.jsgraphql.psi.GraphQLRecursiveVisitor
 import com.intellij.lang.jsgraphql.psi.GraphQLSelectionSet
 import com.intellij.lang.jsgraphql.psi.GraphQLTypeNameDefinition
 import com.intellij.openapi.project.Project
@@ -357,3 +358,19 @@ private fun String.minusOperationTypeSuffix(): String {
     else -> this
   }
 }
+
+fun findFragmentSpreads(project: Project, predicate: (GraphQLFragmentSpread) -> Boolean): List<GraphQLFragmentSpread> {
+  return FileTypeIndex.getFiles(GraphQLFileType.INSTANCE, GlobalSearchScope.allScope(project)).flatMap { virtualFile ->
+    val fragmentSpreads = mutableListOf<GraphQLFragmentSpread>()
+    val visitor = object : GraphQLRecursiveVisitor() {
+      override fun visitFragmentSpread(o: GraphQLFragmentSpread) {
+        super.visitFragmentSpread(o)
+        if (predicate(o)) {
+          fragmentSpreads += o
+        }
+      }
+    }
+    PsiManager.getInstance(project).findFile(virtualFile)?.accept(visitor)
+    fragmentSpreads
+  }
+}

intellij-plugin/src/test/kotlin/com/apollographql/ijplugin/navigation/GraphQLGotoDeclarationHandlerTest.kt

@@ -58,6 +58,7 @@ class GraphQLGotoDeclarationHandlerTest : ApolloTestCase() {
       fromElement = { elementAt<PsiElement>("computerFields")!! },
       toFile = "build/generated/source/apollo/main/com/example/generated/fragment/ComputerFields.kt",
       toElement = { elementAt<KtClass>("class ComputerFields")!! },
+      multipleTarget = true
   )
 
   @Test