[SIL Serialization] Print mismatching SILFunction types on error

The crash on `SILFunction type mismatch` provides little information and
tends to be difficult to reproduce. Let's print some of the available
information and distinguish the two failure sites.

I'm not confident all required information is written down so we may
need to improve this further in the future. This version still crashes
the compiler, we may want a proper type-check to prevent this failure
with a clean diagnostic for the example used here.

rdar://53821031

Author: xymus

lib/SIL/IR/SILType.cpp

@@ -1148,7 +1148,6 @@ std::string SILType::getDebugDescription() const {
     std::string str;
     llvm::raw_string_ostream os(str);
     print(os);
-    str.pop_back(); // Remove trailing newline.
     return str;
   }
 

lib/Serialization/DeserializationErrors.h

@@ -442,6 +442,28 @@ class SILEntityError : public llvm::ErrorInfo<SILEntityError> {
   }
 };
 
+class SILFunctionTypeMismatch : public llvm::ErrorInfo<SILFunctionTypeMismatch> {
+  friend ErrorInfo;
+  static const char ID;
+  void anchor() override;
+
+  StringRef name;
+  std::string descLHS, descRHS;
+public:
+  SILFunctionTypeMismatch(StringRef name, std::string descLHS,
+                          std::string descRHS)
+      : name(name), descLHS(descLHS), descRHS(descRHS) {}
+
+  void log(raw_ostream &OS) const override {
+    OS << "SILFunction type mismatch for '" << name << "': '";
+    OS << descLHS << "' != '" <<  descRHS << "'\n";
+  }
+
+  std::error_code convertToErrorCode() const override {
+    return llvm::inconvertibleErrorCode();
+  }
+};
+
 // Decl was not deserialized because its attributes did not match the filter.
 //
 // \sa getDeclChecked

lib/Serialization/DeserializeSIL.cpp

@@ -48,6 +48,8 @@ using namespace llvm::support;
 
 const char SILEntityError::ID = '\0';
 void SILEntityError::anchor() {}
+const char SILFunctionTypeMismatch::ID = '\0';
+void SILFunctionTypeMismatch::anchor() {}
 
 STATISTIC(NumDeserializedFunc, "Number of deserialized SIL functions");
 
@@ -615,8 +617,13 @@ SILDeserializer::readSILFunctionChecked(DeclID FID, SILFunction *existingFn,
 
   // If we have an existing function, verify that the types match up.
   if (fn) {
-    if (fn->getLoweredType() != ty)
-      return MF->diagnoseFatal("SILFunction type mismatch");
+    if (fn->getLoweredType() != ty) {
+      auto error = llvm::make_error<SILFunctionTypeMismatch>(
+                     name,
+                     fn->getLoweredType().getDebugDescription(),
+                     ty.getDebugDescription());
+      return MF->diagnoseFatal(std::move(error));
+    }
 
     fn->setSerialized(IsSerialized_t(isSerialized));
 
@@ -650,7 +657,7 @@ SILDeserializer::readSILFunctionChecked(DeclID FID, SILFunction *existingFn,
     }
 
     if (fn->isDynamicallyReplaceable() != isDynamic)
-      return MF->diagnoseFatal("SILFunction type mismatch");
+      return MF->diagnoseFatal("SILFunction dynamic replaceable mismatch");
 
   } else {
     // Otherwise, create a new function.

test/Serialization/Recovery/error-sil-function.swift

@@ -0,0 +1,13 @@
+// RUN: not --crash %target-swift-frontend -c %s 2>&1 | %FileCheck %s
+// CHECK: *** DESERIALIZATION FAILURE ***
+// CHECK: SILFunction type mismatch for 'asinf': '$@convention(thin) (Float) -> Float' != '$@convention(c) (Float) -> Float'
+
+// REQUIRES: VENDOR=apple
+
+import Darwin
+
+@_silgen_name("asinf") internal func quux(_ x: Float) -> Float
+
+public func bar(_ x: Float) -> Float {
+  return quux(x)
+}