Export of internal Abseil changes.

--
8f685654a7d04eb8a0cb82d31e44e391e906b609 by Derek Mauro <dmauro@google.com>:

Support constexpr construction of absl::string_view from a
string literal in MSVC 2017+.

Fixes https://github.com/abseil/abseil-cpp/issues/352

PiperOrigin-RevId: 260853160

--
a3c4c5168ce2a491134d7c87cf7fdc75d1ee2533 by Derek Mauro <dmauro@google.com>:

Make SwissTable's at() throw when exceptions are enabled

Fixes https://github.com/abseil/abseil-cpp/issues/355

PiperOrigin-RevId: 260788026
GitOrigin-RevId: 8f685654a7d04eb8a0cb82d31e44e391e906b609
Change-Id: I9ed498e181faa9c9d16e9b1b01404969d99b8ea9

2 files changed, 24 insertions, 11 deletions

diff --git a/absl/strings/string_view.h b/absl/strings/string_view.h
index f8b20015df6a..65b1772de747 100644
--- a/absl/strings/string_view.h
+++ b/absl/strings/string_view.h
@@ -172,19 +172,9 @@ class string_view {
   // Implicit constructor of a `string_view` from nul-terminated `str`. When
   // accepting possibly null strings, use `absl::NullSafeStringView(str)`
   // instead (see below).
-#if ABSL_HAVE_BUILTIN(__builtin_strlen) || \
-    (defined(__GNUC__) && !defined(__clang__))
-  // GCC has __builtin_strlen according to
-  // https://gcc.gnu.org/onlinedocs/gcc-4.7.0/gcc/Other-Builtins.html, but
-  // ABSL_HAVE_BUILTIN doesn't detect that, so we use the extra checks above.
-  // __builtin_strlen is constexpr.
   constexpr string_view(const char* str)  // NOLINT(runtime/explicit)
       : ptr_(str),
-        length_(CheckLengthInternal(str ? __builtin_strlen(str) : 0)) {}
-#else
-  constexpr string_view(const char* str)  // NOLINT(runtime/explicit)
-      : ptr_(str), length_(CheckLengthInternal(str ? strlen(str) : 0)) {}
-#endif
+        length_(str ? CheckLengthInternal(StrlenInternal(str)) : 0) {}
 
   // Implicit constructor of a `string_view` from a `const char*` and length.
   constexpr string_view(const char* data, size_type len)
@@ -495,6 +485,24 @@ class string_view {
     return ABSL_ASSERT(len <= kMaxSize), len;
   }
 
+  static constexpr size_type StrlenInternal(const char* str) {
+#if defined(_MSC_VER) && _MSC_VER >= 1910 && !defined(__clang__)
+    // MSVC 2017+ can evaluate this at compile-time.
+    const char* begin = str;
+    while (*str != '\0') ++str;
+    return str - begin;
+#elif ABSL_HAVE_BUILTIN(__builtin_strlen) || \
+    (defined(__GNUC__) && !defined(__clang__))
+    // GCC has __builtin_strlen according to
+    // https://gcc.gnu.org/onlinedocs/gcc-4.7.0/gcc/Other-Builtins.html, but
+    // ABSL_HAVE_BUILTIN doesn't detect that, so we use the extra checks above.
+    // __builtin_strlen is constexpr.
+    return __builtin_strlen(str);
+#else
+    return str ? strlen(str) : 0;
+#endif
+  }
+
   const char* ptr_;
   size_type length_;
 };
diff --git a/absl/strings/string_view_test.cc b/absl/strings/string_view_test.cc
index 823d8ed4581d..2380e1a377a3 100644
--- a/absl/strings/string_view_test.cc
+++ b/absl/strings/string_view_test.cc
@@ -941,6 +941,11 @@ TEST(StringViewTest, ConstexprCompiles) {
 #error GCC/clang should have constexpr string_view.
 #endif
 
+// MSVC 2017+ should be able to construct a constexpr string_view from a cstr.
+#if defined(_MSC_VER) && _MSC_VER >= 1910
+#define ABSL_HAVE_CONSTEXPR_STRING_VIEW_FROM_CSTR 1
+#endif
+
 #endif  // ABSL_HAVE_STD_STRING_VIEW
 
 #ifdef ABSL_HAVE_CONSTEXPR_STRING_VIEW_FROM_CSTR