============ Contributing ============ .. default-role:: code .. include:: rstcommon.rst .. contents:: Contributing happens via "Pull requests" (PR) on github. Every PR needs to be reviewed before it can be merged and the Continuous Integration should be green. The PR has to be approved by two core developers or by Araq. Writing tests ============= There are 4 types of tests: 1. `runnableExamples` documentation comment tests, ran by `nim doc mymod.nim`:cmd: These end up in documentation and ensure documentation stays in sync with code. 2. separate test files, e.g.: ``tests/stdlib/tos.nim``. In nim repo, `testament`:cmd: (see below) runs all ``$nim/tests/*/t*.nim`` test files; for nimble packages, see https://github.com/nim-lang/nimble#tests. 3. (deprecated) tests in `when isMainModule:` block, ran by `nim r mymod.nim`:cmd:. `nimble test`:cmd: can run those in nimble packages when specified in a `task "test"`. 4. (not preferred) ``.. code-block:: nim`` RST snippets; these should only be used in rst sources, in nim sources `runnableExamples` should now always be preferred to those for several reasons (cleaner syntax, syntax highlights, batched testing, and parameter `rdoccmd` allows customization). Not all the tests follow the convention here, feel free to change the ones that don't. Always leave the code cleaner than you found it. Stdlib ------ Each stdlib module (anything under ``lib/``, e.g. ``lib/pure/os.nim``) should preferably have a corresponding separate test file, e.g. ``tests/stdlib/tos.nim``. The old convention was to add a `when isMainModule:` block in the source file, which only gets executed when the tester is building the file. Each test should be in a separate `block:` statement, such that each has its own scope. Use boolean conditions and `doAssert` for the testing by itself, don't rely on echo statements or similar; in particular, avoid things like `echo "done"`. Don't use `unittest.suite` and `unittest.test`. Sample test: .. code-block:: nim block: # foo doAssert foo(1) == 10 block: # bug #1234 static: doAssert 1+1 == 2 block: # bug #1235 var seq2D = newSeqWith(4, newSeq[bool](2)) seq2D[0][0] = true seq2D[1][0] = true seq2D[0][1] = true doAssert seq2D == @[@[true, true], @[true, false], @[false, false], @[false, false]] # doAssert with `not` can now be done as follows: doAssert not (1 == 2) Always refer to a GitHub issue using the following exact syntax: ``bug #1234`` as shown above, so that it's consistent and easier to search or for tooling. Some browser extensions (e.g. https://github.com/sindresorhus/refined-github) will even turn those in clickable links when it works. Rationale for using a separate test file instead of `when isMainModule:` block: * allows custom compiler flags or testing options (see details below) * faster CI since they can be joined in ``megatest`` (combined into a single test) * avoids making the parser do un-necessary work when a source file is merely imported * avoids mixing source and test code when reporting line of code statistics or code coverage Compiler -------- The tests for the compiler use a testing tool called `testament`:cmd:. They are all located in ``tests/`` (e.g.: ``tests/destructor/tdestructor3.nim``). Each test has its own file. All test files are prefixed with `t`. If you want to create a file for import into another test only, use the prefix `m`. At the beginning of every test is the expected behavior of the test. Possible keys are: - `cmd`: A compilation command template e.g. `nim $target --threads:on $options $file`:cmd: - `output`: The expected output (stdout + stderr), most likely via `echo` - `exitcode`: Exit code of the test (via `exit(number)`) - `errormsg`: The

discard """
  file: "tblock1.nim"
  line: 14
  errormsg: "undeclared identifier: \'ha\'"
"""
# check for forward label and
# for failure when label is not declared

proc main =
  block endLess:
    write(stdout, "Muaahh!\N")
    break endLess

  break ha #ERROR

main()

first 2 lines are for other RST implementations, including Github one. .. [*] this is fulfilled when ``doc/rstcommon.rst`` is included. Best practices ============== Note: these are general guidelines, not hard rules; there are always exceptions. Code reviews can just point to a specific section here to save time and propagate best practices. .. _define_needs_prefix: New `defined(foo)` symbols need to be prefixed by the nimble package name, or by `nim` for symbols in nim sources (e.g. compiler, standard library). This is to avoid name conflicts across packages. .. code-block:: nim # if in nim sources when defined(allocStats): discard # bad, can cause conflicts when defined(nimAllocStats): discard # preferred # if in a package `cligen`: when defined(debug): discard # bad, can cause conflicts when defined(cligenDebug): discard # preferred .. _noimplicitbool: Take advantage of no implicit bool conversion .. code-block:: nim doAssert isValid() == true doAssert isValid() # preferred .. _design_for_mcs: Design with method call syntax chaining in mind .. code-block:: nim proc foo(cond: bool, lines: seq[string]) # bad proc foo(lines: seq[string], cond: bool) # preferred # can be called as: `getLines().foo(false)` .. _avoid_quit: Use exceptions (including `assert` / `doAssert`) instead of `quit` rationale: https://forum.nim-lang.org/t/4089 .. code-block:: nim quit() # bad in almost all cases doAssert() # preferred .. _tests_use_doAssert: Use `doAssert` (or `unittest.check`, `unittest.require`), not `assert` in all tests so they'll be enabled even with `--assertions:off`:option:. .. code-block:: nim block: # foo assert foo() # bad doAssert foo() # preferred .. _runnableExamples_use_assert: An exception to the above rule is `runnableExamples` and ``code-block`` rst blocks intended to be used as `runnableExamples`, which for brevity use `assert` instead of `doAssert`. Note that `nim doc -d:danger main`:cmd: won't pass `-d:danger`:option: to the `runnableExamples`, but `nim doc --doccmd:-d:danger main`:cmd: would, and so would the second example below: .. code-block:: nim runnableExamples: doAssert foo() # bad assert foo() # preferred runnableExamples("-d:danger"): doAssert foo() # `assert` would be disabled here, so `doAssert` makes more sense .. _delegate_printing: Delegate printing to caller: return `string` instead of calling `echo` rationale: it's more flexible (e.g. allows the caller to call custom printing, including prepending location info, writing to log files, etc). .. code-block:: nim proc foo() = echo "bar" # bad proc foo(): string = "bar" # preferred (usually) .. _use_Option: [Ongoing debate] Consider using Option instead of return bool + var argument, unless stack allocation is needed (e.g. for efficiency). .. code-block:: nim proc foo(a: var Bar): bool proc foo(): Option[Bar] .. _use_doAssert_not_echo: Tests (including in testament) should always prefer assertions over `echo`, except when that's not possible. It's more precise, easier for readers and maintainers to where expected values refer to. See for example https://github.com/nim-lang/Nim/pull/9335 and https://forum.nim-lang.org/t/4089 .. code-block:: nim echo foo() # adds a line for testament in `output:` block inside `discard`. doAssert foo() == [1, 2] # preferred, except when not possible to do so. The `git`:cmd: stuff ==================== General commit rules -------------------- 1. Important, critical bugfixes that have a tiny chance of breaking somebody's code should be backported to the latest stable release branch (currently 1.4.x) and maybe also all the way back to the 1.0.x branch. The commit message should contain the tag ``[backport]`` for "backport to the latest stable release" and the tag ``[backport:$VERSION]`` for backporting back to the given $VERSION (and all newer releases). 2. If you introduce changes which affect backward compatibility, make breaking changes, or have PR which is tagged as ``[feature]``, the changes should be mentioned in `the changelog `_. 3. All changes introduced by the commit (diff lines) must be related to the subject of the commit. If you change something unrelated to the subject parts of the file, because your editor reformatted automatically the code or whatever different reason, this should be excluded from the commit. *Tip:* Never commit everything as is using `git commit -a`:cmd:, but review carefully your changes with `git add -p`:cmd:. 4. Changes should not introduce any trailing whitespace. Always check your changes for whitespace errors using `git diff --check`:cmd: or add the following ``pre-commit`` hook: .. code:: cmd #!/bin/sh git diff --check --cached || exit $? 5. Describe your commit and use your common sense. Example commit message:: Fixes #123; refs #124 indicates that issue ``#123`` is completely fixed (GitHub may automatically close it when the PR is committed), wheres issue ``#124`` is referenced (e.g.: partially fixed) and won't close the issue when committed. 6. PR body (not just PR title) should contain references to fixed/referenced github issues, e.g.: ``fix #123`` or ``refs #123``. This is so that you get proper cross referencing from linked issue to the PR (github won't make those links with just PR title, and commit messages aren't always sufficient to ensure that, e.g. can't be changed after a PR is merged). 7. Commits should be always be rebased against devel (so a fast forward merge can happen) e.g.: use `git pull --rebase origin devel`:cmd:. This is to avoid messing up git history. Exceptions should be very rare: when rebase gives too many conflicts, simply squash all commits using the script shown in https://github.com/nim-lang/Nim/pull/9356 8. Do not mix pure formatting changes (e.g. whitespace changes, nimpretty) or automated changes (e.g. nimfix) with other code changes: these should be in separate commits (and the merge on GitHub should not squash these into 1). Continuous Integration (CI) --------------------------- 1. Continuous Integration is by default run on every push in a PR; this clogs the CI pipeline and affects other PR's; if you don't need it (e.g. for WIP or documentation only changes), add ``[skip ci]`` to your commit message title. This convention is supported by our github actions pipelines and our azure pipeline (using custom logic, which should complete in < 1mn) as well as our former other pipelines: `Appveyor `_ and `Travis `_. 2. Consider enabling CI (azure, GitHub actions and builds.sr.ht) in your own Nim fork, and waiting for CI to be green in that fork (fixing bugs as needed) before opening your PR in the original Nim repo, so as to reduce CI congestion. Same applies for updates on a PR: you can test commits on a separate private branch before updating the main PR. Debugging CI failures, flaky tests, etc --------------------------------------- 1. First check the CI logs and search for `FAIL` to find why CI failed; if the failure seems related to your PR, try to fix the code instead of restarting CI. 2. If CI failure seems unrelated to your PR, it could be caused by a flaky test. File a bug for it if it isn't already reported. A PR push (or opening/closing PR) will re-trigger all CI jobs (even successful ones, which can be wasteful). Instead, follow these instructions to only restart the jobs that failed: * Azure: if on your own fork, it's possible from inside azure console (e.g. ``dev.azure.com/username/username/_build/results?buildId=1430&view=results``) via ``rerun failed jobs`` on top. If either on you own fork or in Nim repo, it's possible from inside GitHub UI under checks tab, see https://github.com/timotheecour/Nim/issues/211#issuecomment-629751569 * GitHub actions: under "Checks" tab, click "Re-run jobs" in the right. * builds.sr.ht: create a sourcehut account so you can restart a PR job as illustrated. builds.sr.ht also allows you to ssh to a CI machine which can help a lot for debugging issues, see docs in https://man.sr.ht/builds.sr.ht/build-ssh.md and https://drewdevault.com/2019/08/19/Introducing-shell-access-for-builds.html; see https://man.sr.ht/tutorials/set-up-account-and-git.md to generate and upload ssh keys. Code reviews ------------ 1. Whenever possible, use GitHub's new 'Suggested change' in code reviews, which saves time explaining the change or applying it; see also https://forum.nim-lang.org/t/4317 2. When reviewing large diffs that may involve code moving around, GitHub's interface doesn't help much as it doesn't highlight moves. Instead, you can use something like this, see visual results `here `_: .. code:: cmd git fetch origin pull/10431/head && git checkout FETCH_HEAD git diff --color-moved-ws=allow-indentation-change --color-moved=blocks HEAD^ 3. In addition, you can view GitHub-like diffs locally to identify what was changed within a code block using `diff-highlight`:cmd: or `diff-so-fancy`:cmd:, e.g.: :: # put this in ~/.gitconfig: [core] pager = "diff-so-fancy | less -R" # or: use: `diff-highlight` .. include:: docstyle.rst Evolving the stdlib =================== As outlined in https://github.com/nim-lang/RFCs/issues/173 there are a couple of guidelines about what should go into the stdlib, what should be added and what eventually should be removed. What the compiler itself needs must be part of the stdlib --------------------------------------------------------- Maybe in the future the compiler itself can depend on Nimble packages but for the time being, we strive to have zero dependencies in the compiler as the compiler is the root of the bootstrapping process and is also used to build Nimble. Vocabulary types must be part of the stdlib ------------------------------------------- These are types most packages need to agree on for better interoperability, for example `Option[T]`. This rule also covers the existing collections like `Table`, `CountTable` etc. "Sorted" containers based on a tree-like data structure are still missing and should be added. Time handling, especially the `Time` type are also covered by this rule. Existing, battle-tested modules stay ------------------------------------ Reason: There is no benefit in moving them around just to fullfill some design fashion as in "Nim's core MUST BE SMALL". If you don't like an existing module, don't import it. If a compilation target (e.g. JS) cannot support a module, document this limitation. This covers modules like `os`, `osproc`, `strscans`, `strutils`, `strformat`, etc. Syntactic helpers can start as experimental stdlib modules ---------------------------------------------------------- Reason: Generally speaking as external dependencies they are not exposed to enough users so that we can see if the shortcuts provide enough benefit or not. Many programmers avoid external dependencies, even moreso for "tiny syntactic improvements". However, this is only true for really good syntactic improvements that have the potential to clean up other parts of the Nim library substantially. If in doubt, new stdlib modules should start as external, successful Nimble packages. Other new stdlib modules do not start as stdlib modules ------------------------------------------------------- As we strive for higher quality everywhere, it's easier to adopt existing, battle-tested modules eventually rather than creating modules from scratch. Little additions are acceptable ------------------------------- As long as they are documented and tested well, adding little helpers to existing modules is acceptable. For two reasons: 1. It makes Nim easier to learn and use in the long run. ("Why does sequtils lack a `countIt`? Because version 1.0 happens to have lacked it? Silly...") 2. To encourage contributions. Contributors often start with PRs that add simple things and then they stay and also fix bugs. Nim is an open source project and lives from people's contributions and involvement. Newly introduced issues have to be balanced against motivating new people. We know where to find perfectly designed pieces of software that have no bugs -- these are the systems that nobody uses. Conventions ----------- 1. New stdlib modules should go under ``Nim/lib/std/``. The rationale is to require users to import via `import std/foo` instead of `import foo`, which would cause potential conflicts with nimble packages. Note that this still applies for new modules in existing logical directories, e.g.: use ``lib/std/collections/foo.nim``, not ``lib/pure/collections/foo.nim``. 2. New module names should prefer plural form whenever possible, e.g.: ``std/sums.nim`` instead of ``std/sum.nim``. In particular, this reduces chances of conflicts between module name and the symbols it defines. Furthermore, module names should use `snake_case` and not use capital letters, which cause issues when going from an OS without case sensitivity to an OS with it. Breaking Changes ================ Introducing breaking changes, no matter how well intentioned, creates long-term problems for the community, in particular those looking to promote reusable Nim code in libraries: In the Nim distribution, critical security and bugfixes, language changes and community improvements are bundled in a single distribution - it is difficult to make partial upgrades with only benign changes. When one library depends on a legacy behavior, it can no longer be used together with another library that does not, breaking all downstream applications - the standard library is unique in that it sits at the root of **all** dependency trees. There is a big difference between compile-time breaking changes and run-time breaking changes. Run-time breaking changes ------------------------- Run-time breaking changes are to be avoided at almost all costs: Nim is used for mission critical applications which depend on behaviours that are not covered by the test suite. As such, it's important that changes to the *stable* parts of the standard library are made avoiding changing the existing behaviors, even when the test suite continues to pass. Examples of run-time breaking changes: - Raising exceptions of a new type, compared to what's currently being raised. - Adding unconstrained or poorly constrained generic procs or macros ("hash now works for all `ref T`"): This may cause code to behave differently depending only on which modules are imported - common examples include `==` and `hash`. - Changing behavior of existing functions like: * "Nim's path handling procs like `getXDir` now consistently lack the trailing slash" * "Nim's strformat implementation is now more consistent with Python" Instead write new code that explicitly announces the feature you think we announced but didn't. For example, `strformat` does not say "it's compatible with Python", it says "inspired by Python's f-strings". This new code can be submitted to the stdlib and the old code can be deprecated or it can be published as a Nimble package. Sometimes, a run-time breaking change is most desirable: For example, a string representation of a floating point number that "roundtrips" is much better than a string represenation that doesn't. These run-time breaking changes must start in the state "opt-in" via a new `-d:nimPreviewX` or command line flag and then should become the new default later, in follow-up versions. This way users can track regressions more easily. ("git bisect" is not an acceptable alternative, that's for Nim compiler developers, not for Nim users.) Above all else, additive approaches that don't change existing behaviors should be preferred. Compile-time breaking changes ----------------------------- Compile-time breaking changes are usually easier to handle, but for large code bases it can also be much work and it can hinder the adoption of a new Nim release. Additive approaches are to be preferred here as well. Examples of compile-time breaking changes include (but are not limited to): * Renaming functions and modules, or moving things. Instead of a direct rename, deprecate the old name and introduce a new one. * Renaming the parameter names: Thanks to Nim's "named parameter" calling syntax like `f(x = 0, y = 1)` this is a breaking change. Instead live with the existing parameter names. * Adding an enum value to an existing enum. Nim's exhaustive case statements stop compiling after such a change. Instead consider to introduce new `bool` fields/parameters. This can be impractical though, so we use good judgement and our list of "important packages" to see if it doesn't break too much code out there in practice. * Adding a new proc to an existing stdlib module. However, for aesthetic reasons this is often preferred over introducing a new module with just a single proc inside. We use good judgement and our list of "important packages" to see if it doesn't break too much code out there in practice. The new procs need to be annotated with a `.since` annotation. Compiler/language spec bugfixes ------------------------------- This can even be applied to compiler "bugfixes": If the compiler should have been "pickier" in its handling of `typedesc`, instead of "fixing typedesc handling bugs", consider the following solution: - Spec out how `typedesc` should really work and also spec out the cases where it should not be allowed! - Deprecate `typedesc` and name the new metatype something new like `typeArg`. - Implement the spec. Non-breaking changes -------------------- Examples of changes that are considered non-breaking (or acceptable breaking changes) include: * Creating a new module. * Adding an overload to an already overloaded proc. * Adding new default parameters to an existing proc. It is assumed that you do not use Nim's stdlib procs's addresses (that you don't use them as first class entities). * Changing the calling convention from `nimcall` to `inline` (but first RFC https://github.com/nim-lang/RFCs/issues/396 needs to be implemented). * Changing the behavior from "crashing" into some other, well documented result (including raising a Defect, but not raising an exception that does not inherit from Defect). * Adding new fields to an existing object. Nim's introspection facilities imply that strictly speaking almost every addition can break somebody's code. It is impractical to care about these cases, a change that only affects introspection is not considered to be a breaking change.