[clangd] Fix a hover crash on unsigned 64bit value

[zyounan]

Summary

This patch adapts to D140059, which makes an assumption that the
caller of APSInt::getExtValue promises no narrowing conversion
happens, i.e., from unsigned int64 to signed int64.

It also fixes clangd/clangd#1557.

[zyounan]

Fix comment

[nridge]

clang-tools-extra/clangd/Hover.cpp

396

Just to make sure I'm not missing anything: this comment change is just fixing a pre-existing mistake in the comment (-2^32 was already printed as 0xffffffff00000000), right? i.e. this patch doesn't change how any number is printed

clang-tools-extra/clangd/unittests/HoverTests.cpp

2953

you can just write va^lue and access it as T.point()

[zyounan]

Thank you!

clang-tools-extra/clangd/Hover.cpp

396

No, the patch doesn't change the behavior of the function. 0xfffffffeffffffff actually stands for -(2**32 + 1). :D

[zyounan]

Address comments

[nridge]

Thanks!

clang-tools-extra/clangd/Hover.cpp

void fillFunctionTypeAndParams(HoverInfo &HI, const Decl *D,
   // FIXME: handle variadics.
 }
 
 // Non-negative numbers are printed using min digits
 // 0     => 0x0
 // 100   => 0x64
 // Negative numbers are sign-extended to 32/64 bits
 // -2    => 0xfffffffe
-// -2^32 => 0xfffffffeffffffff
+// -2^32 => 0xffffffff00000000
 static llvm::FormattedNumber printHex(const llvm::APSInt &V) {
-  uint64_t Bits = V.getExtValue();
+  uint64_t Bits = V.getZExtValue();
   if (V.isNegative() && V.getSignificantBits() <= 32)
     return llvm::format_hex(uint32_t(Bits), 0);
   return llvm::format_hex(Bits, 0);
 }
 
 std::optional<std::string> printExprValue(const Expr *E,
                                           const ASTContext &Ctx) {
   // InitListExpr has two forms, syntactic and semantic. They are the same thing

clang-tools-extra/clangd/unittests/HoverTests.cpp

Annotations T(R"cpp(
     struct X { int Y; void [[^setY]](float) { Y = foo(undefined); } };)cpp");
 
   TestTU TU = TestTU::withCode(T.code());
   auto AST = TU.build();
   for (const auto &P : T.points())
     getHover(AST, P, format::getLLVMStyle(), nullptr);
 }
 
+TEST(Hover, NoCrashAPInt64) {
+  Annotations T(R"cpp(
+    constexpr unsigned long value = -1; // wrap around
+    void foo() { va^lue; }
+  )cpp");
+  auto AST = TestTU::withCode(T.code()).build();
+  getHover(AST, T.point(), format::getLLVMStyle(), nullptr);
+}
+
 TEST(Hover, DocsFromMostSpecial) {
   Annotations T(R"cpp(
   // doc1
   template <typename T> class $doc1^X {};
   // doc2
   template <> class $doc2^X<int> {};
   // doc3
   template <typename T> class $doc3^X<T*> {};