Export of internal Abseil changes

--
9beb68204986a015c9cb065b9fae4f9a8879a788 by Abseil Team <absl-team@google.com>:

Move Base64EscapeInternal and CalculateBase64EscapedLenInternal to an internal header.

PiperOrigin-RevId: 288917378

--
90acfbe03b3f9f6de3ffa49c39343dfaa2c5d38c by Greg Falcon <gfalcon@google.com>:

Update macos CI script to support the ALTERNATE_OPTIONS environment variable.

PiperOrigin-RevId: 288913564

--
f1572e870678cdcda6b48cb39780d1ad984e4c1b by Derek Mauro <dmauro@google.com>:

Makes absl::NullSafeStringView constexpr
Fixes https://github.com/abseil/abseil-cpp/issues/583

PiperOrigin-RevId: 288906940

--
d28a8471e32c10caa64bfffe6d6d4d0a8d144013 by Abseil Team <absl-team@google.com>:

absl::GetFlag is lock free for small trivially copyable types.

PiperOrigin-RevId: 288768172

--
2643b8ed1a1dc836b38ab9e46538a1af129ffd67 by Gennadiy Rozental <rogeeff@google.com>:

Eliminate call to callback from flag initialization.

We do not need to have this invocation inside FlagImpl::Init since SetCallback performs invocation anyways. Calling InitCallback from inside of Init complicates separation of value initialization from data guard initialization, which is about to happen.

PiperOrigin-RevId: 288732526

--
22caa880b7a4cb6da34e16a2e064a473c99e880b by Abseil Team <absl-team@google.com>:

Fix the documentation on how to create a null string_view.

PiperOrigin-RevId: 288727968

--
10727c5cadc561837141176f4c9b9717cec9233a by Greg Falcon <gfalcon@google.com>:

Change CI scripts for gcc to use the ALTERNATE_OPTIONS file as well.

PiperOrigin-RevId: 288718855

--
5d1e2dd6c7fb12af8aa4337a0f61872f5f0c5992 by Greg Falcon <gfalcon@google.com>:

Add an option for using inline namespaces in Abseil.

PiperOrigin-RevId: 288614491
GitOrigin-RevId: 9beb68204986a015c9cb065b9fae4f9a8879a788
Change-Id: If9acd46301e3df8cb231b4c16f7ed651bf4fb3c3

2 files changed, 60 insertions, 0 deletions

diff --git a/absl/base/config.h b/absl/base/config.h
index 87f5b4ae..edbf2246 100644
--- a/absl/base/config.h
+++ b/absl/base/config.h
@@ -90,8 +90,42 @@
 // not support forward declarations of its own types, nor does it support
 // user-provided specialization of Abseil templates.  Code that violates these
 // rules may be broken without warning.)
+#if !defined(ABSL_OPTION_USE_INLINE_NAMESPACE) || \
+    !defined(ABSL_OPTION_INLINE_NAMESPACE_NAME)
+#error options.h is misconfigured.
+#endif
+
+// Check that ABSL_OPTION_INLINE_NAMESPACE_NAME is neither "head" nor ""
+#if defined(__cplusplus) && ABSL_OPTION_USE_INLINE_NAMESPACE == 1
+
+#define ABSL_INTERNAL_DO_TOKEN_STR(x) #x
+#define ABSL_INTERNAL_TOKEN_STR(x) ABSL_INTERNAL_DO_TOKEN_STR(x)
+#define ABSL_INTERNAL_INLINE_NAMESPACE_STR \
+  ABSL_INTERNAL_TOKEN_STR(ABSL_OPTION_INLINE_NAMESPACE_NAME)
+
+static_assert(ABSL_INTERNAL_INLINE_NAMESPACE_STR[0] != '\0',
+              "options.h misconfigured: ABSL_OPTION_INLINE_NAMESPACE_NAME must "
+              "not be empty.");
+static_assert(ABSL_INTERNAL_INLINE_NAMESPACE_STR[0] != 'h' ||
+                  ABSL_INTERNAL_INLINE_NAMESPACE_STR[1] != 'e' ||
+                  ABSL_INTERNAL_INLINE_NAMESPACE_STR[2] != 'a' ||
+                  ABSL_INTERNAL_INLINE_NAMESPACE_STR[3] != 'd' ||
+                  ABSL_INTERNAL_INLINE_NAMESPACE_STR[4] != '\0',
+              "options.h misconfigured: ABSL_OPTION_INLINE_NAMESPACE_NAME must "
+              "be changed to a new, unique identifier name.");
+
+#endif
+
+#if ABSL_OPTION_USE_INLINE_NAMESPACE == 0
 #define ABSL_NAMESPACE_BEGIN
 #define ABSL_NAMESPACE_END
+#elif ABSL_OPTION_USE_INLINE_NAMESPACE == 1
+#define ABSL_NAMESPACE_BEGIN \
+  inline namespace ABSL_OPTION_INLINE_NAMESPACE_NAME {
+#define ABSL_NAMESPACE_END }
+#else
+#error options.h is misconfigured.
+#endif
 
 // -----------------------------------------------------------------------------
 // Compiler Feature Checks
diff --git a/absl/base/options.h b/absl/base/options.h
index 3961e63f..592b33b7 100644
--- a/absl/base/options.h
+++ b/absl/base/options.h
@@ -185,4 +185,30 @@
 
 #define ABSL_OPTION_USE_STD_VARIANT 2
 
+
+// ABSL_OPTION_USE_INLINE_NAMESPACE
+// ABSL_OPTION_INLINE_NAMESPACE_NAME
+//
+// These options controls whether all entities in the absl namespace are
+// contained within an inner inline namespace.  This does not affect the
+// user-visible API of Abseil, but it changes the mangled names of all symbols.
+//
+// This can be useful as a version tag if you are distributing Abseil in
+// precompiled form.  This will prevent a binary library build of Abseil with
+// one inline namespace being used with headers configured with a different
+// inline namespace name.  Binary packagers are reminded that Abseil does not
+// guarantee any ABI stability in Abseil, so any update of Abseil or
+// configuration change in such a binary package should be combined with a
+// new, unique value for the inline namespace name.
+//
+// A value of 0 means not to use inline namespaces.
+//
+// A value of 1 means to use an inline namespace with the given name inside
+// namespace absl.  If this is set, ABSL_OPTION_INLINE_NAMESPACE_NAME must also
+// be changed to a new, unique identifier name.  In particular "head" is not
+// allowed.
+
+#define ABSL_OPTION_USE_INLINE_NAMESPACE 0
+#define ABSL_OPTION_INLINE_NAMESPACE_NAME head
+
 #endif  // ABSL_BASE_OPTIONS_H_