Serialization: Error on mismatch between requirements and confirmances

When deserialization a protocol conformance from a binary swiftmodule
file the compiler can encounter inconsistencies caused by stale module
files. Replace the hard crash with a proper error and print the list of
requirements and conformances being compared to stderr for manual
inspection. Recover silently when we can afford to, during indexing or
in LLDB.

Author: xymus

include/swift/AST/DiagnosticsSema.def

@@ -1043,6 +1043,12 @@ ERROR(modularization_issue_conformance_xref_error,none,
 NOTE(modularization_issue_conformance_xref_note,none,
      "Breaks conformances of '%0' to %1",
      (StringRef, DeclName))
+ERROR(modularization_issue_conformance_error,none,
+      "Conformances of '%0' "
+      "do not match requirement signature of %1; "
+      "%2 conformances for %3 requirements",
+      (StringRef, DeclName, unsigned int, unsigned int))
+
 ERROR(reserved_member_name,none,
       "type member must not be named %0, since it would conflict with the"
       " 'foo.%1' expression", (const ValueDecl *, StringRef))

lib/Serialization/Deserialization.cpp

@@ -8739,12 +8739,39 @@ void ModuleFile::finishNormalConformance(NormalProtocolConformance *conformance,
       return req.getKind() == RequirementKind::Conformance;
     };
     auto requirements = proto->getRequirementSignature().getRequirements();
-    if (!allowCompilerErrors() &&
-        conformanceCount != llvm::count_if(requirements,
-                                           isConformanceReq)) {
-      fatal(llvm::make_error<llvm::StringError>(
-          "serialized conformances do not match requirement signature",
-          llvm::inconvertibleErrorCode()));
+    unsigned int conformanceRequirementCount =
+      llvm::count_if(requirements, isConformanceReq);
+    if (conformanceCount != conformanceRequirementCount) {
+      // Mismatch between the number of loaded conformances and the expected
+      // requirements. One or the other likely comes from a stale module.
+
+      if (!enableExtendedDeserializationRecovery()) {
+        // Error and print full context for visual inspection.
+        ASTContext &ctx = getContext();
+        std::string typeStr = conformance->getType()->getString();
+        ctx.Diags.diagnose(getSourceLoc(),
+                       diag::modularization_issue_conformance_error,
+                       typeStr, proto->getName(), conformanceCount,
+                       conformanceRequirementCount);
+        ctx.Diags.flushConsumers();
+
+        // Print context to stderr.
+        PrintOptions Opts;
+        llvm::errs() << "Requirements:\n";
+        for (auto req: requirements) {
+          req.print(llvm::errs(), Opts);
+          llvm::errs() << "\n";
+        }
+
+        llvm::errs() << "Conformances:\n";
+        for (auto req: reqConformances) {
+          req.print(llvm::errs());
+          llvm::errs() << "\n";
+        }
+      }
+
+      conformance->setInvalid();
+      return;
     }
   }
 

test/Serialization/Recovery/conformance-xref.swift

@@ -22,6 +22,29 @@
 // RUN: %target-swift-frontend -typecheck %t/Client.swift -I %t \
 // RUN:   -experimental-allow-module-with-compiler-errors -verify
 
+/// Case 2: Remove a requirement from one lib, leave the other as stale and
+/// rebuild client. Error on the mismatch.
+// RUN: %target-swift-frontend -emit-module %t/ChangingLib.swift -I %t \
+// RUN:   -emit-module-path %t/ChangingLib.swiftmodule \
+// RUN:   -D DROP_REQUIREMENT
+// RUN: not %target-swift-frontend -typecheck %t/Client.swift -I %t \
+// RUN:   2> %t/errors.log
+// RUN: %FileCheck %s --input-file=%t/errors.log \
+// RUN:   --check-prefix CHECK-REMARK-REQUIREMENT
+
+/// No errors when extended recovery is enabled.
+// RUN: %target-swift-frontend -typecheck %t/Client.swift -I %t \
+// RUN:   -experimental-allow-module-with-compiler-errors -verify
+
+/// Combined case: Remove both the conformance and the requirement.
+/// Fail on the removed conformance only as it was first.
+// RUN: %target-swift-frontend -emit-module %t/ChangingLib.swift -I %t \
+// RUN:   -emit-module-path %t/ChangingLib.swiftmodule \
+// RUN:   -D DROP_CONFORMANCE -D DROP_REQUIREMENT
+// RUN: not %target-swift-frontend -typecheck %t/Client.swift -I %t \
+// RUN:   2> %t/errors.log
+// RUN: %FileCheck %s --input-file=%t/errors.log \
+// RUN:   --check-prefixes CHECK-REMARK-CONFORMANCE
 
 //--- ChangingLib.swift
 
@@ -37,7 +60,19 @@ extension Counter: SimpleProto {}
 #endif
 
 public protocol ProtoUser {
+  associatedtype Element
+#if DROP_REQUIREMENT
+// CHECK-REMARK-REQUIREMENT: MiddleLib.swiftmodule:1:1: error: Conformances of 'OneToAThousand' do not match requirement signature of 'ProtoUser'; 5 conformances for 6 requirements
+// CHECK-REMARK-REQUIREMENT: Requirements:
+// Skipping implicits.
+// CHECK-REMARK-REQUIREMENT: Conformances:
+// Skipping implicits.
+// CHECK-REMARK-REQUIREMENT: (specialized_conformance type="OneToAThousand.Impl" protocol="SimpleProto"
+// CHECK-REMARK-REQUIREMENT:   (normal_conformance type="Counter<T>" protocol="SimpleProto" lazy))
+  associatedtype Impl
+#else
   associatedtype Impl: SimpleProto
+#endif
 
   var start: Impl { get }