diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md index a901b4b961..b0fedae00c 100644 --- a/CONTRIBUTING.md +++ b/CONTRIBUTING.md @@ -1,190 +1,191 @@ Contributing to Bitcoin ABC =========================== The Bitcoin ABC project welcomes contributors! This guide is intended to help developers contribute effectively to Bitcoin ABC. Communicating with Developers ----------------------------- To get in contact with ABC developers, we monitor a telegram supergroup. The intent of this group is specifically to facilitate development of Bitcoin-ABC, and to welcome people who wish to participate. https://t.me/joinchat/HCYr50mxRWjA2uLqii-psw Acceptable use of this supergroup includes the following: * Introducing yourself to other ABC developers. * Getting help with your development environment. * Discussing how to complete a patch. It is not for: * Market discussion * Non-constructive criticism Bitcoin ABC Development Philosophy ---------------------------------- Bitcoin ABC aims for fast iteration and continuous integration. This means that there should be quick turnaround for patches to be proposed, reviewed, and committed. Changes should not sit in a queue for long. Here are some tips to help keep the development working as intended. These are guidelines for the normal and expected development process. Developers can use their judgement to deviate from these guidelines when they have a good reason to do so. - Keep each change small and self-contained. - Reach out for a 1-on-1 review so things move quickly. - Land the Diff quickly after it is accepted. - Don't amend changes after the Diff accepted, new Diff for another fix. - Review Diffs from other developers as quickly as possible. - Large changes should be broken into logical chunks that are easy to review, and keep the code in a functional state. - Do not mix moving stuff around with changing stuff. Do changes with renames on their own. - Sometimes you want to replace one subsystem by another implementation, in which case it is not possible to do things incrementally. In such cases, you keep both implementations in the codebase for a while, as described [here](https://www.gamasutra.com/view/news/128325/Opinion_Parallel_Implementations.php) - There are no "development" branches, all Diffs apply to the master branch, and should always improve it (no regressions). - Don't break the build, it is important to keep master green as much as possible. If a Diff is landed, and breaks the build, fix it quickly. If it cannot be fixed quickly, it should be reverted, and re-applied later when it no longer breaks the build. - As soon as you see a bug, you fix it. Do not continue on. Fixing the bug becomes the top priority, more important than completing other tasks. - Automate as much as possible, and spend time on things only humans can do. Here are some handy links for development practices aligned with Bitcoin ABC: +- [Developer Notes](doc/developer-notes.md) - [Statement of Bitcoin ABC Values and Visions](https://www.yours.org/content/bitcoin-abc---our-values-and-vision-a282afaade7c) - How to Do Code Reviews Like a Human [Part 1](https://mtlynch.io/human-code-reviews-1/) [Part 2](https://mtlynch.io/human-code-reviews-2/) - [Large Diffs Are Hurting Your Ability To Ship](https://medium.com/@kurtisnusbaum/large-diffs-are-hurting-your-ability-to-ship-e0b2b41e8acf) - [Stacked Diffs: Keeping Phabricator Diffs Small](https://medium.com/@kurtisnusbaum/stacked-diffs-keeping-phabricator-diffs-small-d9964f4dcfa6) - [Parallel Implementations](https://www.gamasutra.com/view/news/128325/Opinion_Parallel_Implementations.php) - [The Pragmatic Programmer: From Journeyman to Master](https://www.amazon.com/Pragmatic-Programmer-Journeyman-Master/dp/020161622X) - [Advantages of monolithic version control](https://danluu.com/monorepo/) - [The importance of fixing bugs immediately]{https://youtu.be/E2MIpi8pIvY?t=16m0s} Getting set up with the Bitcoin ABC Repository ---------------------------------------------- 1. Create an account at `https://reviews.bitcoinabc.org/` 2. Install Git and Arcanist on your machine Git documentation can be found at: `https://git-scm.com/` Arcanist documentation can be found at: `https://secure.phabricator.com/book/phabricator/article/arcanist_quick_start/` And: `https://secure.phabricator.com/book/phabricator/article/arcanist/` To install these packages on Debian or Ubuntu, type: `sudo apt-get install git arcanist` 3. If you do not already have an SSH key set up, follow these steps: Type: `ssh-keygen -t rsa -b 4096 -C "your_email@example.com"` Enter a file in which to save the key (/home/*username*/.ssh/id_rsa): [Press enter] 4. Upload your SSH public key to reviews.bitcoinabc.org - go to: `https://reviews.bitcoinabc.org/settings/user/*username*/page/ssh/` - Under "SSH Key Actions", Select "Upload Public Key" Paste contents from: `/home/*username*/.ssh/id_rsa.pub` 5. Clone the repository and install Arcanist certificate: ``` git clone ssh://vcs@reviews.bitcoinabc.org:2221/source/bitcoin-abc.git cd bitcoin-abc arc install-certificate ``` Note: Arcanist tooling will tend to fail if your remote origin is set to something other than the above. A common mistake is to clone from Github and then forget to update your remotes. Follow instructions provided by `arc install-certificate` to provide your API token. 6. Code formatting tools If code formatting tools do not install automatically on your system, you may have to install clang-format-4.0 and autopep8. clang-format-4.0.0 can be installed from http://releases.llvm.org/download.html Working with The Bitcoin ABC Repository --------------------------------------- A typical workflow would be: - Create a topic branch in Git for your changes git checkout -b 'my-topic-branch' - Make your changes, and commit them git commit -a -m 'my-commit' - Create a differential with Arcanist arc diff You should add suggested reviewers and a test plan to the commit message. Note that Arcanist is set up to look only at the most-recent commit message, So all you changes for this Diff should be in one Git commit. - For large changes, break them into several Diffs, as described in this [guide](https://medium.com/@kurtisnusbaum/stacked-diffs-keeping-phabricator-diffs-small-d9964f4dcfa6). You can also include "Depends on Dxxx" in the Arcanist message to indicate dependence on other Diffs. - Log into Phabricator to see review and feedback. - Make changes as suggested by the reviewers. You can simply edit the files with my-topic-branch checked out, and then type `arc diff`. Arcanist will give you the option to add uncommited changes. Or, alternatively, you can commit the changes using `git commit -a --am` to add them to the last commit, or squash multiple commits by typing `git rebase -i master`. If you squash, make sure the commit message has the information needed for arcanist (such as the Diff number, reviewers, etc.). - Update your Diff by typing `arc diff` again. - When reviewers approve your Diff, it should be listed as "ready to Land" in Phabricator. When you want to commit your diff to the repository, check out type my-topic-branch in git, then type `arc land`. You have now succesfully committed a change to the Bitcoin ABC repository. - When reviewing a Diff, apply the changeset on your local by using `arc patch D{NNNN}` What to work on --------------- If you are looking for a useful task to contribute to the project, a good place to start is the list of tasks at `https://reviews.bitcoinabc.org/maniphest/`. You can also get in touch with some of the developers in the open BTCForks Slack channel at `https://btcforks.slack.com/` Copyright --------- By contributing to this repository, you agree to license your work under the MIT license unless specified otherwise in `contrib/debian/copyright` or at the top of the file itself. Any work contributed where you are not the original author must contain its license header with the original author(s) and source. diff --git a/doc/developer-notes.md b/doc/developer-notes.md index d8a13e0d34..8fed57313f 100644 --- a/doc/developer-notes.md +++ b/doc/developer-notes.md @@ -1,534 +1,537 @@ Developer Notes =============== Various coding styles have been used during the history of the codebase, and the result is not very consistent. However, we're now trying to converge to a single style, so please use it in new code. Old code will be converted gradually and you are encouraged to use the provided [clang-format-diff script](/contrib/devtools/README.md#clang-format-diffpy) to clean up the patch automatically before submitting a pull request. - Basic rules specified in [src/.clang-format](/src/.clang-format). - Braces on new lines for namespaces, classes, functions, methods. - Braces on the same line for everything else. - 4 space indentation (no tabs) for every block except namespaces. - No indentation for `public`/`protected`/`private` or for `namespace`. - No extra spaces inside parenthesis; don't do ( this ) - No space after function names; one space after `if`, `for` and `while`. - - If an `if` only has a single-statement then-clause, it can appear - on the same line as the if, without braces. In every other case, - braces are required, and the then and else clauses must appear - correctly indented on a new line. + - Always add braces for block statements (e.g. `if`, `for`, `while`). - `++i` is preferred over `i++`. - -Block style example: + - Use CamelCase for functions/methods, and lowerCamelCase for variables. + - GLOBAL_CONSTANTS should use UPPER_SNAKE_CASE. + - namespaces should use lower_snake_case. + - Function names should generally start with an English command-form verb + (e.g. `ValidateTransaction`, `AddTransactionToMempool`, `ConnectBlock`) + - Variable names should generally be nouns or past/future tense verbs. + (e.g. `canDoThing`, `signatureOperations`, `didThing`) + - Avoid using globals, remove existing globals whenever possible. + - Class member variable names should be prepended with `m_` + - DO choose easily readable identifier names. + - DO favor readability over brevity. + - DO NOT use Hungarian notation. + - DO NOT use abbreviations or contractions within identifiers. + - WRONG: mempool + - RIGHT: MemoryPool + - WRONG: ChangeDir + - RIGHT: ChangeDirectory + - DO NOT use obscure acronyms, DO uppercase any acronyms. + - FINALLY, do not migrate existing code unless refactoring. It makes + forwarding-porting from Bitcoin Core more difficult. + +The naming convention roughly mirrors [Microsoft Naming Conventions](https://docs.microsoft.com/en-us/dotnet/standard/design-guidelines/general-naming-conventions) + +C++ Coding Standards should strive to follow the [LLVM Coding Standards](https://llvm.org/docs/CodingStandards.html) + +Code style example: ```c++ -namespace foo -{ -class Class -{ - bool Function(const std::string& s, int n) - { - // Comment summarising what this section of code does +// namespaces should be lower_snake_case +namespace foo_bar_bob { + +/** + * Class is used for doing classy things. All classes should + * have a doxygen comment describing their PURPOSE. That is to say, + * why they exist. Functional details can be determined from the code. + * @see PerformTask() + */ +class Class { +private: + //! memberVariable's name should be lowerCamelCase, and be a noun. + int m_memberVariable; + +public: + /** + * The documentation before a function or class method should follow Doxygen + * spec. The name of the function should start with an english verb which + * indicates the intended purpose of this code. + * + * The function name should be should be CamelCase. + * + * @param[in] s A description + * @param[in] n Another argument description + * @pre Precondition for function... + */ + bool PerformTask(const std::string& s, int n) { + // Use lowerChamelCase for local variables. + bool didMore = false; + + // Comment summarizing the intended purpose of this section of code for (int i = 0; i < n; ++i) { - // When something fails, return early - if (!Something()) return false; + if (!DidSomethingFail()) { + return false; + } ... - if (SomethingElse()) { + if (IsSomethingElse()) { DoMore(); + didMore = true; } else { DoLess(); } } - // Success return is usually at the end - return true; + return didMore; } } } ``` + Doxygen comments ----------------- To facilitate the generation of documentation, use doxygen-compatible comment blocks for functions, methods and fields. For example, to describe a function use: ```c++ /** * ... text ... * @param[in] arg1 A description * @param[in] arg2 Another argument description * @pre Precondition for function... */ bool function(int arg1, const char *arg2) ``` A complete list of `@xxx` commands can be found at http://www.stack.nl/~dimitri/doxygen/manual/commands.html. As Doxygen recognizes the comments by the delimiters (`/**` and `*/` in this case), you don't *need* to provide any commands for a comment to be valid; just a description text is fine. To describe a class use the same construct above the class definition: ```c++ /** * Alerts are for notifying old versions if they become too obsolete and * need to upgrade. The message is displayed in the status bar. * @see GetWarnings() */ class CAlert { ``` To describe a member or variable use: ```c++ int var; //!< Detailed description after the member ``` or ```cpp //! Description before the member int var; ``` Also OK: ```c++ /// /// ... text ... /// bool function2(int arg1, const char *arg2) ``` Not OK (used plenty in the current source, but not picked up): ```c++ // // ... text ... // ``` A full list of comment syntaxes picked up by doxygen can be found at http://www.stack.nl/~dimitri/doxygen/manual/docblocks.html, but if possible use one of the above styles. To build doxygen locally to test changes to the Doxyfile or visualize your comments before landing changes: ``` # at the project root, call: doxygen doc/Doxyfile # output goes to doc/doxygen/html/ ``` Development tips and tricks --------------------------- **compiling for debugging** Run configure with the --enable-debug option, then make. Or run configure with CXXFLAGS="-g -ggdb -O0" or whatever debug flags you need. **debug.log** If the code is behaving strangely, take a look in the debug.log file in the data directory; error and debugging messages are written there. The -debug=... command-line option controls debugging; running with just -debug or -debug=1 will turn on all categories (and give you a very large debug.log file). The Qt code routes qDebug() output to debug.log under category "qt": run with -debug=qt to see it. **running and debugging tests** Unit tests are run via `make check` For running functional tests, see `/test/README.md` Simple example of debugging unit tests with GDB on Linux: ``` cd /build/src/test gdb test_bitcoin break interpreter.cpp:295 # No path is necessary, just the file name and line number run # GDB hits the breakpoint p/x opcode # print the value of the variable (in this case, opcode) in hex c # continue ``` Simple example of debugging unit tests with LLDB (OSX or Linux): ``` cd /build/src/test lldb -- test_bitcoin break set --file interpreter.cpp --line 295 run ``` **testnet and regtest modes** Run with the -testnet option to run with "play bitcoins" on the test network, if you are testing multi-machine code that needs to operate across the internet. If you are testing something that can run on one machine, run with the -regtest option. In regression test mode, blocks can be created on-demand; see test/functional/ for tests that run in -regtest mode. **DEBUG_LOCKORDER** Bitcoin Core is a multithreaded application, and deadlocks or other multithreading bugs can be very difficult to track down. Compiling with -DDEBUG_LOCKORDER (configure CXXFLAGS="-DDEBUG_LOCKORDER -g") inserts run-time checks to keep track of which locks are held, and adds warnings to the debug.log file if inconsistencies are detected. Locking/mutex usage notes ------------------------- The code is multi-threaded, and uses mutexes and the LOCK/TRY_LOCK macros to protect data structures. Deadlocks due to inconsistent lock ordering (thread 1 locks cs_main and then cs_wallet, while thread 2 locks them in the opposite order: result, deadlock as each waits for the other to release its lock) are a problem. Compile with -DDEBUG_LOCKORDER to get lock order inconsistencies reported in the debug.log file. Re-architecting the core code so there are better-defined interfaces between the various components is a goal, with any necessary locking done by the components (e.g. see the self-contained CKeyStore class and its cs_KeyStore lock for example). Threads ------- - ThreadScriptCheck : Verifies block scripts. - ThreadImport : Loads blocks from blk*.dat files or bootstrap.dat. - StartNode : Starts other threads. - ThreadDNSAddressSeed : Loads addresses of peers from the DNS. - ThreadMapPort : Universal plug-and-play startup/shutdown - ThreadSocketHandler : Sends/Receives data from peers on port 8333. - ThreadOpenAddedConnections : Opens network connections to added nodes. - ThreadOpenConnections : Initiates new connections to peers. - ThreadMessageHandler : Higher-level message handling (sending and receiving). - DumpAddresses : Dumps IP addresses of nodes to peers.dat. - ThreadFlushWalletDB : Close the wallet.dat file if it hasn't been used in 500ms. - ThreadRPCServer : Remote procedure call handler, listens on port 8332 for connections and services them. - BitcoinMiner : Generates bitcoins (if wallet is enabled). - Shutdown : Does an orderly shutdown of everything. Ignoring IDE/editor files -------------------------- In closed-source environments in which everyone uses the same IDE it is common to add temporary files it produces to the project-wide `.gitignore` file. However, in open source software such as Bitcoin Core, where everyone uses their own editors/IDE/tools, it is less common. Only you know what files your editor produces and this may change from version to version. The canonical way to do this is thus to create your local gitignore. Add this to `~/.gitconfig`: ``` [core] excludesfile = /home/.../.gitignore_global ``` (alternatively, type the command `git config --global core.excludesfile ~/.gitignore_global` on a terminal) Then put your favourite tool's temporary filenames in that file, e.g. ``` # NetBeans nbproject/ ``` Another option is to create a per-repository excludes file `.git/info/exclude`. These are not committed but apply only to one repository. If a set of tools is used by the build system or scripts the repository (for example, lcov) it is perfectly acceptable to add its files to `.gitignore` and commit them. Development guidelines ============================ A few non-style-related recommendations for developers, as well as points to pay attention to for reviewers of Bitcoin Core code. -General Bitcoin Core ----------------------- - -- New features should be exposed on RPC first, then can be made available in the GUI - - - *Rationale*: RPC allows for better automatic testing. The test suite for - the GUI is very limited - -- Make sure pull requests pass Travis CI before merging - - - *Rationale*: Makes sure that they pass thorough testing, and that the tester will keep passing - on the master branch. Otherwise all new pull requests will start failing the tests, resulting in - confusion and mayhem - - - *Explanation*: If the test suite is to be updated for a change, this has to - be done first - Wallet ------- - Make sure that no crashes happen with run-time option `-disablewallet`. - *Rationale*: In RPC code that conditionally uses the wallet (such as `validateaddress`) it is easy to forget that global pointer `pwalletMain` can be NULL. See `test/functional/disablewallet.py` for functional tests exercising the API with `-disablewallet` - Include `db_cxx.h` (BerkeleyDB header) only when `ENABLE_WALLET` is set - *Rationale*: Otherwise compilation of the disable-wallet build will fail in environments without BerkeleyDB General C++ ------------- - Assertions should not have side-effects - *Rationale*: Even though the source code is set to to refuse to compile with assertions disabled, having side-effects in assertions is unexpected and makes the code harder to understand - If you use the `.h`, you must link the `.cpp` - *Rationale*: Include files define the interface for the code in implementation files. Including one but not linking the other is confusing. Please avoid that. Moving functions from the `.h` to the `.cpp` should not result in build errors - Use the RAII (Resource Acquisition Is Initialization) paradigm where possible. For example by using `unique_ptr` for allocations in a function. - *Rationale*: This avoids memory and resource leaks, and ensures exception safety C++ data structures -------------------- - Never use the `std::map []` syntax when reading from a map, but instead use `.find()` - *Rationale*: `[]` does an insert (of the default element) if the item doesn't exist in the map yet. This has resulted in memory leaks in the past, as well as race conditions (expecting read-read behavior). Using `[]` is fine for *writing* to a map - Do not compare an iterator from one data structure with an iterator of another data structure (even if of the same type) - *Rationale*: Behavior is undefined. In C++ parlor this means "may reformat the universe", in practice this has resulted in at least one hard-to-debug crash bug - Watch out for out-of-bounds vector access. `&vch[vch.size()]` is illegal, including `&vch[0]` for an empty vector. Use `vch.data()` and `vch.data() + vch.size()` instead. - Vector bounds checking is only enabled in debug mode. Do not rely on it - Make sure that constructors initialize all fields. If this is skipped for a good reason (i.e., optimization on the critical path), add an explicit comment about this - *Rationale*: Ensure determinism by avoiding accidental use of uninitialized values. Also, static analyzers balk about this. - Use explicitly signed or unsigned `char`s, or even better `uint8_t` and `int8_t`. Do not use bare `char` unless it is to pass to a third-party API. This type can be signed or unsigned depending on the architecture, which can lead to interoperability problems or dangerous conditions such as out-of-bounds array accesses - Prefer explicit constructions over implicit ones that rely on 'magical' C++ behavior - *Rationale*: Easier to understand what is happening, thus easier to spot mistakes, even for those that are not language lawyers Strings and formatting ------------------------ -- Be careful of `LogPrint` versus `LogPrintf`. `LogPrint` takes a `category` argument, `LogPrintf` does not. - - - *Rationale*: Confusion of these can result in runtime exceptions due to - formatting mismatch, and it is easy to get wrong because of subtly similar naming - - Use `std::string`, avoid C string manipulation functions - *Rationale*: C++ string handling is marginally safer, less scope for buffer overflows and surprises with `\0` characters. Also some C string manipulations tend to act differently depending on platform, or even the user locale - Use `ParseInt32`, `ParseInt64`, `ParseUInt32`, `ParseUInt64`, `ParseDouble` from `utilstrencodings.h` for number parsing - *Rationale*: These functions do overflow checking, and avoid pesky locale issues -- For `strprintf`, `LogPrint`, `LogPrintf` formatting characters don't need size specifiers - - - *Rationale*: Bitcoin Core uses tinyformat, which is type safe. Leave them out to avoid confusion - Variable names -------------- The shadowing warning (`-Wshadow`) is enabled by default. It prevents issues rising from using a different variable with the same name. Please name variables so that their names do not shadow variables defined in the source code. -E.g. in member initializers, prepend `_` to the argument name shadowing the -member name: - -```c++ -class AddressBookPage -{ - Mode mode; -} - -AddressBookPage::AddressBookPage(Mode _mode) : - mode(_mode) -... -``` - -When using nested cycles, do not name the inner cycle variable the same as in -upper cycle etc. - - Threads and synchronization ---------------------------- - Build and run tests with `-DDEBUG_LOCKORDER` to verify that no potential deadlocks are introduced. As of 0.12, this is defined by default when configuring with `--enable-debug` - When using `LOCK`/`TRY_LOCK` be aware that the lock exists in the context of the current scope, so surround the statement and the code that needs the lock with braces OK: ```c++ { TRY_LOCK(cs_vNodes, lockNodes); ... } ``` Wrong: ```c++ TRY_LOCK(cs_vNodes, lockNodes); { ... } ``` Source code organization -------------------------- - Implementation code should go into the `.cpp` file and not the `.h`, unless necessary due to template usage or when performance due to inlining is critical - *Rationale*: Shorter and simpler header files are easier to read, and reduce compile time - Don't import anything into the global namespace (`using namespace ...`). Use fully specified types such as `std::string`. - *Rationale*: Avoids symbol conflicts GUI ----- - Do not display or manipulate dialogs in model code (classes `*Model`) - *Rationale*: Model classes pass through events and data from the core, they should not interact with the user. That's where View classes come in. The converse also holds: try to not directly access core data structures from Views. Subtrees ---------- Several parts of the repository are subtrees of software maintained elsewhere. Some of these are maintained by active developers of Bitcoin Core, in which case changes should probably go directly upstream without being PRed directly against the project. They will be merged back in the next subtree merge. Others are external projects without a tight relationship with our project. Changes to these should also be sent upstream but bugfixes may also be prudent to PR against Bitcoin Core so that they can be integrated quickly. Cosmetic changes should be purely taken upstream. There is a tool in contrib/devtools/git-subtree-check.sh to check a subtree directory for consistency with its upstream repository. Current subtrees include: - src/leveldb - Upstream at https://github.com/google/leveldb ; Maintained by Google, but open important PRs to Core to avoid delay - src/libsecp256k1 - Upstream at https://github.com/bitcoin-core/secp256k1/ ; actively maintaned by Core contributors. - src/crypto/ctaes - Upstream at https://github.com/bitcoin-core/ctaes ; actively maintained by Core contributors. - src/univalue - Upstream at https://github.com/jgarzik/univalue ; report important PRs to Core to avoid delay. Git and GitHub tips --------------------- - Github is not typically the source of truth for pull requests. See CONTRIBUTING.md for instructions on setting up your repo correctly. - Similarly, your git remote origin should be set to: `ssh://vcs@reviews.bitcoinabc.org:2221/source/bitcoin-abc.git` instead of github.com. See CONTRIBUTING.md for details. - For resolving merge/rebase conflicts, it can be useful to enable diff3 style using `git config merge.conflictstyle diff3`. Instead of <<< yours === theirs >>> you will see <<< yours ||| original === theirs >>> This may make it much clearer what caused the conflict. In this style, you can often just look at what changed between *original* and *theirs*, and mechanically apply that to *yours* (or the other way around). - When reviewing patches which change indentation in C++ files, use `git diff -w` and `git show -w`. This makes the diff algorithm ignore whitespace changes. This feature is also available on github.com, by adding `?w=1` at the end of any URL which shows a diff. - When reviewing patches that change symbol names in many places, use `git diff --word-diff`. This will instead of showing the patch as deleted/added *lines*, show deleted/added *words*. - When reviewing patches that move code around, try using `git diff --patience commit~:old/file.cpp commit:new/file/name.cpp`, and ignoring everything except the moved body of code which should show up as neither `+` or `-` lines. In case it was not a pure move, this may even work when combined with the `-w` or `--word-diff` options described above. - When looking at other's pull requests, it may make sense to add the following section to your `.git/config` file: [remote "upstream-pull"] fetch = +refs/pull/*:refs/remotes/upstream-pull/* url = git@github.com:bitcoin/bitcoin.git This will add an `upstream-pull` remote to your git repository, which can be fetched using `git fetch --all` or `git fetch upstream-pull`. Afterwards, you can use `upstream-pull/NUMBER/head` in arguments to `git show`, `git checkout` and anywhere a commit id would be acceptable to see the changes from pull request NUMBER.