Fix concurrent access crash. Closes #232

Author: ileitch

CHANGELOG.md

@@ -10,7 +10,7 @@
 
 ##### Bug Fixes
 
-- None.
+- Fix crash during indexing phase.
 
 ## 2.3.0 (2020-12-05)
 

Sources/PeripheryKit/Indexer/SourceGraph.swift

@@ -98,15 +98,19 @@ public final class SourceGraph {
 
     func remove(_ declaration: Declaration) {
         mutationQueue.sync {
-            declaration.parent?.declarations.remove(declaration)
-            allDeclarations.remove(declaration)
-            allDeclarationsByKind[declaration.kind]?.remove(declaration)
-            rootDeclarations.remove(declaration)
-            reachableDeclarations.remove(declaration)
-            declaration.usrs.forEach { allExplicitDeclarationsByUsr.removeValue(forKey: $0) }
+            removeUnsafe(declaration)
         }
     }
 
+    func removeUnsafe(_ declaration: Declaration) {
+        declaration.parent?.declarations.remove(declaration)
+        allDeclarations.remove(declaration)
+        allDeclarationsByKind[declaration.kind]?.remove(declaration)
+        rootDeclarations.remove(declaration)
+        reachableDeclarations.remove(declaration)
+        declaration.usrs.forEach { allExplicitDeclarationsByUsr.removeValue(forKey: $0) }
+    }
+
     func add(_ reference: Reference) {
         mutationQueue.sync {
             _ = allReferences.insert(reference)

Sources/PeripheryKit/Indexer/SwiftIndexer.swift

@@ -216,32 +216,30 @@ public final class SwiftIndexer {
         private var varParameterUsrs: Set<String> = []
 
         private func establishDeclarationHierarchy() {
-            for (parent, decls) in childDeclsByParentUsr {
-                guard let parentDecl = graph.explicitDeclaration(withUsr: parent) else {
-                    if varParameterUsrs.contains(parent) {
-                        // These declarations are children of a parameter and are redundant.
-                        decls.forEach { graph.remove($0) }
-                    }
+            graph.mutating {
+                for (parent, decls) in childDeclsByParentUsr {
+                    guard let parentDecl = graph.explicitDeclaration(withUsr: parent) else {
+                        if varParameterUsrs.contains(parent) {
+                            // These declarations are children of a parameter and are redundant.
+                            decls.forEach { graph.removeUnsafe($0) }
+                        }
 
-                    continue
-                }
+                        continue
+                    }
 
-                graph.mutating {
                     for decl in decls {
                         decl.parent = parentDecl
                     }
 
                     parentDecl.declarations.formUnion(decls)
                 }
-            }
 
-            for (usr, references) in referencedDeclsByUsr {
-                guard let decl = graph.explicitDeclaration(withUsr: usr) else {
-                    danglingReferences.append(contentsOf: references)
-                    continue
-                }
+                for (usr, references) in referencedDeclsByUsr {
+                    guard let decl = graph.explicitDeclaration(withUsr: usr) else {
+                        danglingReferences.append(contentsOf: references)
+                        continue
+                    }
 
-                graph.mutating {
                     for reference in references {
                         reference.parent = decl
 
@@ -252,9 +250,7 @@ public final class SwiftIndexer {
                         }
                     }
                 }
-            }
 
-            graph.mutating {
                 for (decl, refs) in referencedUsrsByDecl {
                     for ref in refs {
                         ref.parent = decl