Bail On Checking Invalid Precedence Group

When the user spells an invalid precedence group, the Relation for that
group will fail to resolve the decl. We need to handle this in
checkPrecedenceGroup. Also add some asserts while I'm here.

rdar://75248642

Author: CodaFi

include/swift/AST/Decl.h

@@ -6977,6 +6977,11 @@ class PrecedenceGroupDecl : public Decl {
     return HigherThanLoc;
   }
 
+  /// Retrieve the array of \c Relation objects containing those precedence
+  /// groups with higher precedence than this precedence group.
+  ///
+  /// The elements of this array may be invalid, in which case they will have
+  /// null \c PrecedenceGroupDecl elements.
   ArrayRef<Relation> getHigherThan() const {
     return { getHigherThanBuffer(), NumHigherThan };
   }
@@ -6994,6 +6999,11 @@ class PrecedenceGroupDecl : public Decl {
     return LowerThanLoc;
   }
 
+  /// Retrieve the array of \c Relation objects containing those precedence
+  /// groups with lower precedence than this precedence group.
+  ///
+  /// The elements of this array may be invalid, in which case they will have
+  /// null \c PrecedenceGroupDecl elements.
   ArrayRef<Relation> getLowerThan() const {
     return { getLowerThanBuffer(), NumLowerThan };
   }

lib/Sema/TypeCheckAccess.cpp

@@ -1797,6 +1797,12 @@ class DeclAvailabilityChecker : public DeclVisitor<DeclAvailabilityChecker> {
   void checkPrecedenceGroup(const PrecedenceGroupDecl *PGD,
                             const Decl *refDecl, SourceLoc diagLoc,
                             SourceRange refRange) {
+    // Bail on invalid predence groups. This can happen when the user spells a
+    // relation element that doesn't actually exist.
+    if (!PGD) {
+      return;
+    }
+
     const SourceFile *SF = refDecl->getDeclContext()->getParentSourceFile();
     ModuleDecl *M = PGD->getModuleContext();
     if (!SF->isImportedImplementationOnly(M))

lib/Serialization/Serialization.cpp

@@ -3158,10 +3158,14 @@ class Serializer::DeclSerializer : public DeclVisitor<DeclSerializer> {
     auto associativity = getRawStableAssociativity(group->getAssociativity());
 
     SmallVector<DeclID, 8> relations;
-    for (auto &rel : group->getHigherThan())
+    for (auto &rel : group->getHigherThan()) {
+      assert(rel.Group && "Undiagnosed invalid precedence group!");
       relations.push_back(S.addDeclRef(rel.Group));
-    for (auto &rel : group->getLowerThan())
+    }
+    for (auto &rel : group->getLowerThan()) {
+      assert(rel.Group && "Undiagnosed invalid precedence group!");
       relations.push_back(S.addDeclRef(rel.Group));
+    }
 
     unsigned abbrCode = S.DeclTypeAbbrCodes[PrecedenceGroupLayout::Code];
     PrecedenceGroupLayout::emitRecord(S.Out, S.ScratchRecord, abbrCode,

validation-test/compiler_crashers_2_fixed/rdar75248642.swift

@@ -0,0 +1,8 @@
+// RUN: not %target-swift-frontend -typecheck %s
+
+precedencegroup MyOperatorPrecedence {
+  lowerThan: MultiplicationPrecedence
+  higherThan: AdditionPrec
+  associativity: left
+  assignment: false
+}