Export of internal Abseil changes

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

Move Base64EscapeInternal and CalculateBase64EscapedLenInternal to an internal header.

PiperOrigin-RevId: 288917378

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

Update macos CI script to support the ALTERNATE_OPTIONS environment variable.

PiperOrigin-RevId: 288913564

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

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

PiperOrigin-RevId: 288906940

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

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

PiperOrigin-RevId: 288768172

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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

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

Fix the documentation on how to create a null string_view.

PiperOrigin-RevId: 288727968

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

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

PiperOrigin-RevId: 288718855

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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, 238 insertions, 0 deletions

diff --git a/absl/strings/internal/escaping.cc b/absl/strings/internal/escaping.cc
new file mode 100644
index 000000000000..c5271286ad00
--- /dev/null
+++ b/absl/strings/internal/escaping.cc
@@ -0,0 +1,180 @@
+// Copyright 2020 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/internal/escaping.h"
+
+#include "absl/base/internal/endian.h"
+#include "absl/base/internal/raw_logging.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace strings_internal {
+
+const char kBase64Chars[] =
+    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
+
+size_t CalculateBase64EscapedLenInternal(size_t input_len, bool do_padding) {
+  // Base64 encodes three bytes of input at a time. If the input is not
+  // divisible by three, we pad as appropriate.
+  //
+  // (from https://tools.ietf.org/html/rfc3548)
+  // Special processing is performed if fewer than 24 bits are available
+  // at the end of the data being encoded.  A full encoding quantum is
+  // always completed at the end of a quantity.  When fewer than 24 input
+  // bits are available in an input group, zero bits are added (on the
+  // right) to form an integral number of 6-bit groups.  Padding at the
+  // end of the data is performed using the '=' character.  Since all base
+  // 64 input is an integral number of octets, only the following cases
+  // can arise:
+
+  // Base64 encodes each three bytes of input into four bytes of output.
+  size_t len = (input_len / 3) * 4;
+
+  if (input_len % 3 == 0) {
+    // (from https://tools.ietf.org/html/rfc3548)
+    // (1) the final quantum of encoding input is an integral multiple of 24
+    // bits; here, the final unit of encoded output will be an integral
+    // multiple of 4 characters with no "=" padding,
+  } else if (input_len % 3 == 1) {
+    // (from https://tools.ietf.org/html/rfc3548)
+    // (2) the final quantum of encoding input is exactly 8 bits; here, the
+    // final unit of encoded output will be two characters followed by two
+    // "=" padding characters, or
+    len += 2;
+    if (do_padding) {
+      len += 2;
+    }
+  } else {  // (input_len % 3 == 2)
+    // (from https://tools.ietf.org/html/rfc3548)
+    // (3) the final quantum of encoding input is exactly 16 bits; here, the
+    // final unit of encoded output will be three characters followed by one
+    // "=" padding character.
+    len += 3;
+    if (do_padding) {
+      len += 1;
+    }
+  }
+
+  assert(len >= input_len);  // make sure we didn't overflow
+  return len;
+}
+
+size_t Base64EscapeInternal(const unsigned char* src, size_t szsrc, char* dest,
+                            size_t szdest, const char* base64,
+                            bool do_padding) {
+  static const char kPad64 = '=';
+
+  if (szsrc * 4 > szdest * 3) return 0;
+
+  char* cur_dest = dest;
+  const unsigned char* cur_src = src;
+
+  char* const limit_dest = dest + szdest;
+  const unsigned char* const limit_src = src + szsrc;
+
+  // Three bytes of data encodes to four characters of cyphertext.
+  // So we can pump through three-byte chunks atomically.
+  if (szsrc >= 3) {                    // "limit_src - 3" is UB if szsrc < 3.
+    while (cur_src < limit_src - 3) {  // While we have >= 32 bits.
+      uint32_t in = absl::big_endian::Load32(cur_src) >> 8;
+
+      cur_dest[0] = base64[in >> 18];
+      in &= 0x3FFFF;
+      cur_dest[1] = base64[in >> 12];
+      in &= 0xFFF;
+      cur_dest[2] = base64[in >> 6];
+      in &= 0x3F;
+      cur_dest[3] = base64[in];
+
+      cur_dest += 4;
+      cur_src += 3;
+    }
+  }
+  // To save time, we didn't update szdest or szsrc in the loop.  So do it now.
+  szdest = limit_dest - cur_dest;
+  szsrc = limit_src - cur_src;
+
+  /* now deal with the tail (<=3 bytes) */
+  switch (szsrc) {
+    case 0:
+      // Nothing left; nothing more to do.
+      break;
+    case 1: {
+      // One byte left: this encodes to two characters, and (optionally)
+      // two pad characters to round out the four-character cypherblock.
+      if (szdest < 2) return 0;
+      uint32_t in = cur_src[0];
+      cur_dest[0] = base64[in >> 2];
+      in &= 0x3;
+      cur_dest[1] = base64[in << 4];
+      cur_dest += 2;
+      szdest -= 2;
+      if (do_padding) {
+        if (szdest < 2) return 0;
+        cur_dest[0] = kPad64;
+        cur_dest[1] = kPad64;
+        cur_dest += 2;
+        szdest -= 2;
+      }
+      break;
+    }
+    case 2: {
+      // Two bytes left: this encodes to three characters, and (optionally)
+      // one pad character to round out the four-character cypherblock.
+      if (szdest < 3) return 0;
+      uint32_t in = absl::big_endian::Load16(cur_src);
+      cur_dest[0] = base64[in >> 10];
+      in &= 0x3FF;
+      cur_dest[1] = base64[in >> 4];
+      in &= 0x00F;
+      cur_dest[2] = base64[in << 2];
+      cur_dest += 3;
+      szdest -= 3;
+      if (do_padding) {
+        if (szdest < 1) return 0;
+        cur_dest[0] = kPad64;
+        cur_dest += 1;
+        szdest -= 1;
+      }
+      break;
+    }
+    case 3: {
+      // Three bytes left: same as in the big loop above.  We can't do this in
+      // the loop because the loop above always reads 4 bytes, and the fourth
+      // byte is past the end of the input.
+      if (szdest < 4) return 0;
+      uint32_t in = (cur_src[0] << 16) + absl::big_endian::Load16(cur_src + 1);
+      cur_dest[0] = base64[in >> 18];
+      in &= 0x3FFFF;
+      cur_dest[1] = base64[in >> 12];
+      in &= 0xFFF;
+      cur_dest[2] = base64[in >> 6];
+      in &= 0x3F;
+      cur_dest[3] = base64[in];
+      cur_dest += 4;
+      szdest -= 4;
+      break;
+    }
+    default:
+      // Should not be reached: blocks of 4 bytes are handled
+      // in the while loop before this switch statement.
+      ABSL_RAW_LOG(FATAL, "Logic problem? szsrc = %zu", szsrc);
+      break;
+  }
+  return (cur_dest - dest);
+}
+
+}  // namespace strings_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
diff --git a/absl/strings/internal/escaping.h b/absl/strings/internal/escaping.h
new file mode 100644
index 000000000000..6a9ce602d9ed
--- /dev/null
+++ b/absl/strings/internal/escaping.h
@@ -0,0 +1,58 @@
+// Copyright 2020 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef ABSL_STRINGS_INTERNAL_ESCAPING_H_
+#define ABSL_STRINGS_INTERNAL_ESCAPING_H_
+
+#include <cassert>
+
+#include "absl/strings/internal/resize_uninitialized.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace strings_internal {
+
+ABSL_CONST_INIT extern const char kBase64Chars[];
+
+// Calculates how long a string will be when it is base64 encoded given its
+// length and whether or not the result should be padded.
+size_t CalculateBase64EscapedLenInternal(size_t input_len, bool do_padding);
+
+// Base64-encodes `src` using the alphabet provided in `base64` and writes the
+// result to `dest`. If `do_padding` is true, `dest` is padded with '=' chars
+// until its length is a multiple of 3. Returns the length of `dest`.
+size_t Base64EscapeInternal(const unsigned char* src, size_t szsrc, char* dest,
+                            size_t szdest, const char* base64, bool do_padding);
+
+// Base64-encodes `src` using the alphabet provided in `base64` and writes the
+// result to `dest`. If `do_padding` is true, `dest` is padded with '=' chars
+// until its length is a multiple of 3.
+template <typename String>
+void Base64EscapeInternal(const unsigned char* src, size_t szsrc, String* dest,
+                          bool do_padding, const char* base64_chars) {
+  const size_t calc_escaped_size =
+      CalculateBase64EscapedLenInternal(szsrc, do_padding);
+  STLStringResizeUninitialized(dest, calc_escaped_size);
+
+  const size_t escaped_len = Base64EscapeInternal(
+      src, szsrc, &(*dest)[0], dest->size(), base64_chars, do_padding);
+  assert(calc_escaped_size == escaped_len);
+  dest->erase(escaped_len);
+}
+
+}  // namespace strings_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_STRINGS_INTERNAL_ESCAPING_H_