[clang-format] [PR35518] C++17 deduction guides are wrongly formatted

Summary:
see https://bugs.llvm.org/show_bug.cgi?id=35518

clang-format removes spaces around deduction guides but not trailing return types, make the consistent

```
template <typename T> S(T)->S<T>;
auto f(int, int) -> double;
```

becomes

```
template <typename T> S(T) -> S<T>;
auto f(int, int) -> double;
```

Reviewers: klimek, mitchell-stellar, owenpan, sammccall, lichray, curdeius, KyrBoh

Reviewed By: curdeius

Subscribers: merge_guards_bot, hans, lichray, cfe-commits

Tags: #clang-format, #clang-tools-extra, #clang

Differential Revision: https://reviews.llvm.org/D69577

1 files changed, 23 insertions, 0 deletions

diff --git a/clang/unittests/Format/FormatTest.cpp b/clang/unittests/Format/FormatTest.cpp
index ea03ee1c3cc..eacb389400b 100644
--- a/clang/unittests/Format/FormatTest.cpp
+++ b/clang/unittests/Format/FormatTest.cpp
@@ -4977,6 +4977,29 @@ TEST_F(FormatTest, TrailingReturnType) {
   verifyFormat("void f() { auto a = b->c(); }");
 }
 
+TEST_F(FormatTest, DeductionGuides) {
+  verifyFormat("template <class T> A(const T &, const T &) -> A<T &>;");
+  verifyFormat("template <class T> explicit A(T &, T &&) -> A<T>;");
+  verifyFormat("template <class... Ts> S(Ts...) -> S<Ts...>;");
+  verifyFormat(
+      "template <class... T>\n"
+      "array(T &&... t) -> array<std::common_type_t<T...>, sizeof...(T)>;");
+  verifyFormat("template <class T> A() -> A<decltype(p->foo<3>())>;");
+  verifyFormat("template <class T> A() -> A<decltype(foo<traits<1>>)>;");
+  verifyFormat("template <class T> A() -> A<sizeof(p->foo<1>)>;");
+  verifyFormat("template <class T> A() -> A<(3 < 2)>;");
+  verifyFormat("template <class T> A() -> A<((3) < (2))>;");
+  verifyFormat("template <class T> x() -> x<1>;");
+  verifyFormat("template <class T> explicit x(T &) -> x<1>;");
+
+  // Ensure not deduction guides.
+  verifyFormat("c()->f<int>();");
+  verifyFormat("x()->foo<1>;");
+  verifyFormat("x = p->foo<3>();");
+  verifyFormat("x()->x<1>();");
+  verifyFormat("x()->x<1>;");
+}
+
 TEST_F(FormatTest, BreaksFunctionDeclarationsWithTrailingTokens) {
   // Avoid breaking before trailing 'const' or other trailing annotations, if
   // they are not function-like.