tvl-depot/nix/buildkite/default.nix
sterni c59e11dc3e fix(nix/buildkite): solve bogus realpath errors if build steps fail
- Set pipefail to make sure the correct exit code gets returned.

- Don't let xargs(1) call realpath(1) if the build fails (and nothing is
  printed to stdout).

Change-Id: I526a18df877601d884b83862da5f37336cdf52cd
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11312
Autosubmit: sterni <sternenseemann@systemli.org>
Tested-by: BuildkiteCI
Reviewed-by: flokli <flokli@flokli.de>
2024-04-03 11:52:10 +00:00

454 lines
17 KiB
Nix

# Logic for generating Buildkite pipelines from Nix build targets read
# by //nix/readTree.
#
# It outputs a "YAML" (actually JSON) file which is evaluated and
# submitted to Buildkite at the start of each build.
#
# The structure of the file that is being created is documented here:
# https://buildkite.com/docs/pipelines/defining-steps
{ depot, pkgs, ... }:
let
inherit (builtins)
attrValues
concatLists
concatStringsSep
elem
foldl'
hasAttr
hashString
isNull
isString
length
listToAttrs
mapAttrs
toJSON
unsafeDiscardStringContext;
inherit (pkgs) lib runCommand writeText;
inherit (depot.nix.readTree) mkLabel;
in
rec {
# Given an arbitrary attribute path generate a Nix expression which obtains
# this from the root of depot (assumed to be ./.). Attributes may be any
# Nix strings suitable as attribute names, not just Nix literal-safe strings.
mkBuildExpr = attrPath:
let
descend = expr: attr: "builtins.getAttr \"${attr}\" (${expr})";
in
foldl' descend "import ./. {}" attrPath;
# Determine whether to skip a target if it has not diverged from the
# HEAD branch.
shouldSkip = { parentTargetMap ? { }, label, drvPath }:
if (hasAttr label parentTargetMap) && parentTargetMap."${label}".drvPath == drvPath
then "Target has not changed."
else false;
# Create build command for an attribute path pointing to a derivation.
mkBuildCommand = { attrPath, drvPath, outLink ? "result" }: concatStringsSep " " [
# If the nix build fails, the Nix command's exit status should be used.
"set -o pipefail;"
# First try to realise the drvPath of the target so we don't evaluate twice.
# Nix has no concept of depending on a derivation file without depending on
# at least one of its `outPath`s, so we need to discard the string context
# if we don't want to build everything during pipeline construction.
#
# To make this more uniform with how nix-build(1) works, we call realpath(1)
# on nix-store(1)'s output since it has the habit of printing the path of the
# out link, not the store path.
"(nix-store --realise '${drvPath}' --add-root '${outLink}' --indirect | xargs -r realpath)"
# Since we don't gcroot the derivation files, they may be deleted by the
# garbage collector. In that case we can reevaluate and build the attribute
# using nix-build.
"|| (test ! -f '${drvPath}' && nix-build -E '${mkBuildExpr attrPath}' --show-trace --out-link '${outLink}')"
];
# Attribute path of a target relative to the depot root. Needs to take into
# account whether the target is a physical target (which corresponds to a path
# in the filesystem) or the subtarget of a physical target.
targetAttrPath = target:
target.__readTree
++ lib.optionals (target ? __subtarget) [ target.__subtarget ];
# Create a pipeline step from a single target.
mkStep = { headBranch, parentTargetMap, target, cancelOnBuildFailing }:
let
label = mkLabel target;
drvPath = unsafeDiscardStringContext target.drvPath;
in
{
label = ":nix: " + label;
key = hashString "sha1" label;
skip = shouldSkip { inherit label drvPath parentTargetMap; };
command = mkBuildCommand {
attrPath = targetAttrPath target;
inherit drvPath;
};
env.READTREE_TARGET = label;
cancel_on_build_failing = cancelOnBuildFailing;
# Add a dependency on the initial static pipeline step which
# always runs. This allows build steps uploaded in batches to
# start running before all batches have been uploaded.
depends_on = [ ":init:" ] ++ lib.optionals (target ? meta.ci.buildkiteExtraDeps) target.meta.ci.buildkiteExtraDeps;
} // lib.optionalAttrs (target ? meta.timeout) {
timeout_in_minutes = target.meta.timeout / 60;
# Additional arguments to set on the step.
# Keep in mind these *overwrite* existing step args, not extend. Use with caution.
} // lib.optionalAttrs (target ? meta.ci.buildkiteExtraStepArgs) target.meta.ci.buildkiteExtraStepArgs;
# Helper function to inelegantly divide a list into chunks of at
# most n elements.
#
# This works by assigning each element a chunk ID based on its
# index, and then grouping all elements by their chunk ID.
chunksOf = n: list:
let
chunkId = idx: toString (idx / n + 1);
assigned = lib.imap1 (idx: value: { inherit value; chunk = chunkId idx; }) list;
unchunk = mapAttrs (_: elements: map (e: e.value) elements);
in
unchunk (lib.groupBy (e: e.chunk) assigned);
# Define a build pipeline chunk as a JSON file, using the pipeline
# format documented on
# https://buildkite.com/docs/pipelines/defining-steps.
makePipelineChunk = name: chunkId: chunk: rec {
filename = "${name}-chunk-${chunkId}.json";
path = writeText filename (toJSON {
steps = chunk;
});
};
# Split the pipeline into chunks of at most 192 steps at once, which
# are uploaded sequentially. This is because of a limitation in the
# Buildkite backend which struggles to process more than a specific
# number of chunks at once.
pipelineChunks = name: steps:
attrValues (mapAttrs (makePipelineChunk name) (chunksOf 192 steps));
# Create a pipeline structure for the given targets.
mkPipeline =
{
# HEAD branch of the repository on which release steps, GC
# anchoring and other "mainline only" steps should run.
headBranch
, # List of derivations as read by readTree (in most cases just the
# output of readTree.gather) that should be built in Buildkite.
#
# These are scheduled as the first build steps and run as fast as
# possible, in order, without any concurrency restrictions.
drvTargets
, # Derivation map of a parent commit. Only targets which no longer
# correspond to the content of this map will be built. Passing an
# empty map will always build all targets.
parentTargetMap ? { }
, # A list of plain Buildkite step structures to run alongside the
# build for all drvTargets, but before proceeding with any
# post-build actions such as status reporting.
#
# Can be used for things like code formatting checks.
additionalSteps ? [ ]
, # A list of plain Buildkite step structures to run after all
# previous steps succeeded.
#
# Can be used for status reporting steps and the like.
postBuildSteps ? [ ]
# The list of phases known by the current Buildkite
# pipeline. Dynamic pipeline chunks for each phase are uploaded
# to Buildkite on execution of static part of the
# pipeline. Phases selection is hard-coded in the static
# pipeline.
#
# Pipeline generation will fail when an extra step with
# unregistered phase is added.
#
# Common scenarios for different phase:
# - "build" - main phase for building all Nix targets
# - "release" - pushing artifacts to external repositories
# - "deploy" - updating external deployment configurations
, phases ? [ "build" "release" ]
# Build phases that are active for this invocation (i.e. their
# steps should be generated).
#
# This can be used to disable outputting parts of a pipeline if,
# for example, build and release phases are created in separate
# eval contexts.
#
# TODO(tazjin): Fail/warn if unknown phase is requested.
, activePhases ? phases
# Setting this attribute to true cancels dynamic pipeline steps
# as soon as the build is marked as failing.
#
# To enable this feature one should enable "Fail Fast" setting
# at Buildkite pipeline or on organization level.
, cancelOnBuildFailing ? false
}:
let
# List of phases to include.
enabledPhases = lib.intersectLists activePhases phases;
# Is the 'build' phase included? This phase is treated specially
# because it always contains the plain Nix builds, and some
# logic/optimisation depends on knowing whether is executing.
buildEnabled = elem "build" enabledPhases;
# Convert a target into all of its steps, separated by build
# phase (as phases end up in different chunks).
targetToSteps = target:
let
mkStepArgs = {
inherit headBranch parentTargetMap target cancelOnBuildFailing;
};
step = mkStep mkStepArgs;
# Same step, but with an override function applied. This is
# used in mkExtraStep if the extra step needs to modify the
# parent derivation somehow.
#
# Note that this will never affect the label.
overridable = f: mkStep (mkStepArgs // { target = (f target); });
# Split extra steps by phase.
splitExtraSteps = lib.groupBy ({ phase, ... }: phase)
(attrValues (mapAttrs (normaliseExtraStep phases overridable)
(target.meta.ci.extraSteps or { })));
extraSteps = mapAttrs
(_: steps:
map (mkExtraStep (targetAttrPath target) buildEnabled) steps)
splitExtraSteps;
in
if !buildEnabled then extraSteps
else extraSteps // {
build = [ step ] ++ (extraSteps.build or [ ]);
};
# Combine all target steps into step lists per phase.
#
# TODO(tazjin): Refactor when configurable phases show up.
globalSteps = {
build = additionalSteps;
release = postBuildSteps;
};
phasesWithSteps = lib.zipAttrsWithNames enabledPhases (_: concatLists)
((map targetToSteps drvTargets) ++ [ globalSteps ]);
# Generate pipeline chunks for each phase.
chunks = foldl'
(acc: phase:
let phaseSteps = phasesWithSteps.${phase} or [ ]; in
if phaseSteps == [ ]
then acc
else acc ++ (pipelineChunks phase phaseSteps))
[ ]
enabledPhases;
in
runCommand "buildkite-pipeline" { } ''
mkdir $out
echo "Generated ${toString (length chunks)} pipeline chunks"
${
lib.concatMapStringsSep "\n"
(chunk: "cp ${chunk.path} $out/${chunk.filename}") chunks
}
'';
# Create a drvmap structure for the given targets, containing the
# mapping of all target paths to their derivations. The mapping can
# be persisted for future use.
mkDrvmap = drvTargets: writeText "drvmap.json" (toJSON (listToAttrs (map
(target: {
name = mkLabel target;
value = {
drvPath = unsafeDiscardStringContext target.drvPath;
# Include the attrPath in the output to reconstruct the drv
# without parsing the human-readable label.
attrPath = targetAttrPath target;
};
})
drvTargets)));
# Implementation of extra step logic.
#
# Each target extra step is an attribute specified in
# `meta.ci.extraSteps`. Its attribute name will be used as the step
# name on Buildkite.
#
# command (required): A command that will be run in the depot
# checkout when this step is executed. Should be a derivation
# resulting in a single executable file, e.g. through
# pkgs.writeShellScript.
#
# label (optional): Human-readable label for this step to display
# in the Buildkite UI instead of the attribute name.
#
# prompt (optional): Setting this blocks the step until confirmed
# by a human. Should be a string which is displayed for
# confirmation. These steps always run after the main build is
# done and have no influence on CI status.
#
# needsOutput (optional): If set to true, the parent derivation
# will be built in the working directory before running the
# command. Output will be available as 'result'.
# TODO: Figure out multiple-output derivations.
#
# parentOverride (optional): A function (drv -> drv) to override
# the parent's target definition when preparing its output. Only
# used in extra steps that use needsOutput.
#
# branches (optional): Git references (branches, tags ... ) on
# which this step should be allowed to run. List of strings.
#
# alwaysRun (optional): If set to true, this step will always run,
# even if its parent has not been rebuilt.
#
# Note that gated steps are independent of each other.
# Create a gated step in a step group, independent from any other
# steps.
mkGatedStep = { step, label, parent, prompt }: {
inherit (step) depends_on;
group = label;
skip = parent.skip or false;
steps = [
{
inherit prompt;
branches = step.branches or [ ];
block = ":radio_button: Run ${label}? (from ${parent.env.READTREE_TARGET})";
}
# The explicit depends_on of the wrapped step must be removed,
# otherwise its dependency relationship with the gate step will
# break.
(builtins.removeAttrs step [ "depends_on" ])
];
};
# Validate and normalise extra step configuration before actually
# generating build steps, in order to use user-provided metadata
# during the pipeline generation.
normaliseExtraStep = phases: overridableParent: key:
{ command
, label ? key
, needsOutput ? false
, parentOverride ? (x: x)
, branches ? null
, alwaysRun ? false
, prompt ? false
, softFail ? false
, phase ? "build"
, skip ? false
, agents ? null
}:
let
parent = overridableParent parentOverride;
parentLabel = parent.env.READTREE_TARGET;
validPhase = lib.throwIfNot (elem phase phases) ''
In step '${label}' (from ${parentLabel}):
Phase '${phase}' is not valid.
Known phases: ${concatStringsSep ", " phases}
''
phase;
in
{
inherit
alwaysRun
branches
command
key
label
needsOutput
parent
parentLabel
softFail
skip
agents;
phase = validPhase;
prompt = lib.throwIf (prompt != false && phase == "build") ''
In step '${label}' (from ${parentLabel}):
The 'prompt' feature can only be used by steps in the "release"
phase, because CI builds should not be gated on manual human
approvals.
''
prompt;
};
# Create the Buildkite configuration for an extra step, optionally
# wrapping it in a gate group.
mkExtraStep = parentAttrPath: buildEnabled: cfg:
let
# ATTN: needs to match an entry in .gitignore so that the tree won't get dirty
commandScriptLink = "nix-buildkite-extra-step-command-script";
step = {
key = hashString "sha1" "${cfg.label}-${cfg.parentLabel}";
label = ":gear: ${cfg.label} (from ${cfg.parentLabel})";
skip =
let
# When parent doesn't have skip attribute set, default to false
parentSkip = cfg.parent.skip or false;
# Extra step skip parameter can be string explaining the
# skip reason.
extraStepSkip = if builtins.isString cfg.skip then true else cfg.skip;
# Don't run if extra step is explicitly set to skip. If
# parameter is not set or equal to false, follow parent behavior.
skip' = if extraStepSkip then cfg.skip else parentSkip;
in
if cfg.alwaysRun then false else skip';
depends_on = lib.optional
(buildEnabled && !cfg.alwaysRun && !cfg.needsOutput)
cfg.parent.key;
command = pkgs.writeShellScript "${cfg.key}-script" ''
set -ueo pipefail
${lib.optionalString cfg.needsOutput
"echo '~~~ Preparing build output of ${cfg.parentLabel}'"
}
${lib.optionalString cfg.needsOutput cfg.parent.command}
echo '--- Building extra step script'
command_script="$(${
# Using command substitution in this way assumes the script drv only has one output
assert builtins.length cfg.command.outputs == 1;
mkBuildCommand {
# script is exposed at <parent>.meta.ci.extraSteps.<key>.command
attrPath =
parentAttrPath
++ [ "meta" "ci" "extraSteps" cfg.key "command" ];
drvPath = unsafeDiscardStringContext cfg.command.drvPath;
# make sure it doesn't conflict with result (from needsOutput)
outLink = commandScriptLink;
}
})"
echo '+++ Running extra step script'
exec "$command_script"
'';
soft_fail = cfg.softFail;
} // (lib.optionalAttrs (cfg.agents != null) { inherit (cfg) agents; })
// (lib.optionalAttrs (cfg.branches != null) {
branches = lib.concatStringsSep " " cfg.branches;
});
in
if (isString cfg.prompt)
then
mkGatedStep
{
inherit step;
inherit (cfg) label parent prompt;
}
else step;
}