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revlog: skeleton support for version 2 revlogs...
revlog: skeleton support for version 2 revlogs There are a number of improvements we want to make to revlogs that will require a new version - version 2. It is unclear what the full set of improvements will be or when we'll be done with them. What I do know is that the process will likely take longer than a single release, will require input from various stakeholders to evaluate changes, and will have many contentious debates and bikeshedding. It is unrealistic to develop revlog version 2 up front: there are just too many uncertainties that we won't know until things are implemented and experiments are run. Some changes will also be invasive and prone to bit rot, so sitting on dozens of patches is not practical. This commit introduces skeleton support for version 2 revlogs in a way that is flexible and not bound by backwards compatibility concerns. An experimental repo requirement for denoting revlog v2 has been added. The requirement string has a sub-version component to it. This will allow us to declare multiple requirements in the course of developing revlog v2. Whenever we change the in-development revlog v2 format, we can tweak the string, creating a new requirement and locking out old clients. This will allow us to make as many backwards incompatible changes and experiments to revlog v2 as we want. In other words, we can land code and make meaningful progress towards revlog v2 while still maintaining extreme format flexibility up until the point we freeze the format and remove the experimental labels. To enable the new repo requirement, you must supply an experimental and undocumented config option. But not just any boolean flag will do: you need to explicitly use a value that no sane person should ever type. This is an additional guard against enabling revlog v2 on an installation it shouldn't be enabled on. The specific scenario I'm trying to prevent is say a user with a 4.4 client with a frozen format enabling the option but then downgrading to 4.3 and accidentally creating repos with an outdated and unsupported repo format. Requiring a "challenge" string should prevent this. Because the format is not yet finalized and I don't want to take any chances, revlog v2's version is currently 0xDEAD. I figure squatting on a value we're likely never to use as an actual revlog version to mean "internal testing only" is acceptable. And "dead" is easily recognized as something meaningful. There is a bunch of cleanup that is needed before work on revlog v2 begins in earnest. I plan on doing that work once this patch is accepted and we're comfortable with the idea of starting down this path.
Gregory Szorc - - Load All Authors

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error_private.c
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/ contrib / python-zstandard / zstd / common / error_private.c
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Gregory Szorc
zstd: vendor zstd 1.1.1...
 r30434 /**
* Copyright (c) 2016-present, Yann Collet, Facebook, Inc.
* All rights reserved.
*
* This source code is licensed under the BSD-style license found in the
* LICENSE file in the root directory of this source tree. An additional grant
* of patent rights can be found in the PATENTS file in the same directory.
*/
/* The purpose of this file is to have a single list of error strings embedded in binary */
#include "error_private.h"
const char* ERR_getErrorString(ERR_enum code)
{
static const char* const notErrorCode = "Unspecified error code";
switch( code )
{
case PREFIX(no_error): return "No error detected";
case PREFIX(GENERIC): return "Error (generic)";
case PREFIX(prefix_unknown): return "Unknown frame descriptor";
case PREFIX(version_unsupported): return "Version not supported";
case PREFIX(parameter_unknown): return "Unknown parameter type";
case PREFIX(frameParameter_unsupported): return "Unsupported frame parameter";
case PREFIX(frameParameter_unsupportedBy32bits): return "Frame parameter unsupported in 32-bits mode";
case PREFIX(frameParameter_windowTooLarge): return "Frame requires too much memory for decoding";
case PREFIX(compressionParameter_unsupported): return "Compression parameter is out of bound";
case PREFIX(init_missing): return "Context should be init first";
case PREFIX(memory_allocation): return "Allocation error : not enough memory";
case PREFIX(stage_wrong): return "Operation not authorized at current processing stage";
case PREFIX(dstSize_tooSmall): return "Destination buffer is too small";
case PREFIX(srcSize_wrong): return "Src size incorrect";
case PREFIX(corruption_detected): return "Corrupted block detected";
case PREFIX(checksum_wrong): return "Restored data doesn't match checksum";
case PREFIX(tableLog_tooLarge): return "tableLog requires too much memory : unsupported";
case PREFIX(maxSymbolValue_tooLarge): return "Unsupported max Symbol Value : too large";
case PREFIX(maxSymbolValue_tooSmall): return "Specified maxSymbolValue is too small";
case PREFIX(dictionary_corrupted): return "Dictionary is corrupted";
case PREFIX(dictionary_wrong): return "Dictionary mismatch";
case PREFIX(maxCode):
default: return notErrorCode;
}
}