Run make prepush's checks concurrently

Makefile

@@ -217,12 +217,21 @@ ci-nosetup:
 
 # Run the fast jobs.
 # This is designed for developers, to be run often and before submitting code upstream.
+#
+# These jobs write to separate target-triple subdirectories, so run them
+# concurrently once format-check (cheap, fails fast) passes on its own.
+# Only default our own -j if the user didn't pass one -- a submake's own
+# -j always overrides a parent's instead of merging with it. --output-sync
+# needs make >= 4.0 (e.g. macOS's bundled make is 3.81), so only pass it
+# if supported, since an unknown flag is a hard error, not a graceful skip.
+NPROC := $(or $(shell nproc 2>/dev/null),$(shell sysctl -n hw.ncpu 2>/dev/null),4)
+JOBS := $(if $(filter -j% --jobserver%,$(MAKEFLAGS)),,-j$(NPROC))
+OSYNC := $(if $(filter-out 0 1 2 3,$(firstword $(subst ., ,$(MAKE_VERSION)))),--output-sync=target,)
 .PHONY: prepush
-prepush:\
-	format-check\
-	ci-job-clippy\
-	ci-job-syntax\
-	licensecheck
+prepush:
+	@$(MAKE) format-check
+	@$(MAKE) $(OSYNC) $(JOBS) \
+		ci-job-clippy ci-job-syntax licensecheck
 	$(call banner,Pre-Push checks all passed!)
 	# Note: Tock runs additional and more intense CI checks on all PRs.
 	# If one of these error, you can run `make ci-job-NAME` to test locally.
@@ -401,21 +410,42 @@ ci-job-readme-check:
 
 
 ### ci-runner-github-clippy jobs:
+#
+# One board per `arch/*` crate actually in use (tools/build/list_arch_boards.sh),
+# so clippy checks every architecture's target-specific code without
+# checking every board.
+#
+# Split into sub-targets so `make -j` can run them concurrently instead of
+# back-to-back. They share one workspace `target/` dir, so on a clean
+# checkout they still partly serialize on `-Zbuild-std`'s lock; cached
+# (normal) runs don't.
+#
+# $(shell) doesn't fail the build on a nonzero exit, so an empty result
+# (the script errored, or a future change left it with nothing to say)
+# would otherwise silently generate zero board-specific clippy rules
+# below instead of failing loudly. Checked in ci-job-clippy's own recipe,
+# not a top-level $(error): this assignment runs on every `make`
+# invocation regardless of target (Make expands all rule headers up
+# front), so failing here would take down unrelated targets like `make
+# clean` whenever this script breaks.
+CLIPPY_ARCH_BOARDS := $(shell ./tools/build/list_arch_boards.sh)
+
 .PHONY: ci-job-clippy
-ci-job-clippy:
-	$(call banner,CI-Job: Clippy)
+ci-job-clippy: ci-job-clippy-workspace $(foreach b,$(CLIPPY_ARCH_BOARDS),ci-job-clippy-$(subst /,-,$(b)))
+	@test -n "$(CLIPPY_ARCH_BOARDS)" || (echo "error: list_arch_boards.sh returned no boards -- check it succeeded" >&2; exit 1)
+
+.PHONY: ci-job-clippy-workspace
+ci-job-clippy-workspace:
+	$(call banner,CI-Job: Clippy (workspace))
 	@cargo clippy -- -D warnings
-	# Run `cargo clippy` in select boards so we run clippy with targets that
-	# actually check the arch-specific functions.
-	# 
-	# - nrf52840dk: cortex-m4
-	# - raspberry_pi_pico: cortex-m0
-	# - hifive1: riscv
-	# - qemu_i486_q35: x86
-	@cd boards/nordic/nrf52840dk && cargo clippy -- -D warnings
-	@cd boards/raspberry_pi_pico && cargo clippy -- -D warnings
-	@cd boards/hifive1 && cargo clippy -- -D warnings
-	@cd boards/qemu_i486_q35 && cargo clippy -Zjson-target-spec -- -D warnings
+
+define clippy_arch_board_rule
+.PHONY: ci-job-clippy-$(subst /,-,$(1))
+ci-job-clippy-$(subst /,-,$(1)):
+	$$(call banner,CI-Job: Clippy ($(1)))
+	@cd boards/$(1) && cargo clippy -- -D warnings
+endef
+$(foreach b,$(CLIPPY_ARCH_BOARDS),$(eval $(call clippy_arch_board_rule,$(b))))
 
 
 
@@ -427,10 +457,14 @@ ci-job-clippy:
 # `rustflags` a crate already sets via its own `.cargo/config.toml`.
 DENY_WARNINGS_CARGO_CONFIG := $(CURDIR)/boards/cargo/deny_warnings.toml
 
+# Calls `cargo check` directly rather than via `$(MAKE) allcheck`: a
+# recursive $(MAKE) here bypasses --output-sync=target's buffering (the
+# child manages its own output), so under a parallel `prepush` its
+# compile output could land in the middle of another job's block.
 .PHONY: ci-job-syntax
 ci-job-syntax:
 	$(call banner,CI-Job: Syntax)
-	@TOCK_CARGO_FLAGS="--config $(DENY_WARNINGS_CARGO_CONFIG)" $(MAKE) allcheck
+	@cargo check --config $(DENY_WARNINGS_CARGO_CONFIG)
 
 .PHONY: ci-job-compilation
 ci-job-compilation:

boards/qemu_i486_q35/.cargo/config.toml

@@ -7,13 +7,16 @@ include = [
   "../../cargo/unstable_flags.toml",
 ]
 
-[env]
-# Relative to crate root, not this file
-# TODO: where is the best place to store this config file?
-RUST_TARGET_PATH = "."
-
 [build]
 target = "i486-unknown-none.json"
 
 [target.i486-unknown-none]
 runner = "qemu-system-i386 -cpu 486 -machine q35 -net none -device isa-debug-exit,iobase=0xf4,iosize=0x04 -device virtio-rng-pci,disable-legacy=on -serial stdio -kernel"
+
+# `target` above is a bare filename, not a path -- cargo only resolves that
+# as a custom target spec (rather than requiring a builtin triple name) with
+# this enabled. Same mechanism ../../cargo/riscv_flags.toml uses for the
+# RISC-V boards' JSON specs, just needed explicitly here since those are
+# referenced by relative path instead.
+[unstable]
+json-target-spec = true

boards/qemu_i486_q35/Makefile

@@ -8,10 +8,6 @@
 # Skip auto-installing targets with rustup, since we are using a custom target
 NO_RUSTUP := 1
 
-# Because we use a custom target with a .json file, we must pass
-# `-Zjson-target-spec` to cargo as of roughly January 2026.
-CARGO = cargo -Zjson-target-spec
-
 include ../Makefile.common
 
 QEMU_CMD             := qemu-system-i386

tools/build/list_arch_boards.sh

@@ -0,0 +1,67 @@
+#!/usr/bin/env bash
+
+# Licensed under the Apache License, Version 2.0 or the MIT License.
+# SPDX-License-Identifier: Apache-2.0 OR MIT
+# Copyright Tock Contributors 2026.
+
+# For each arch/* crate, print one representative board: the
+# alphabetically-first board that depends on it, directly or via its chip.
+#
+# Reasonably aware of arch dependencies (i.e., `cortexm` picked up by `cortexm7`), and
+# avoids duplicates where unneeded (but, e.g., `cortexm4` also necessarily repeats `cortexm`).
+#
+# Variants of another board (extra feature/policy configs, tutorial
+# copies) are skipped, same as boards/README.md's own tooling, since
+# they're not independent ports and would just be redundant picks.
+# Sorted once so the loop below can stop at the first (alphabetical) match.
+boards=($(./tools/build/list_boards.sh | sort | grep -vE '^(configurations|tutorials)/'))
+
+# True if $board depends on arch/$arch, directly or via its chip.
+board_depends_on_arch() {
+    local board="$1" arch="$2"
+    local board_toml="boards/$board/Cargo.toml"
+    # Matches a `path = "…/arch/$arch"` dependency line; some Cargo.toml
+    # files omit the whitespace around `=`.
+    local pattern="path[[:space:]]*=[[:space:]]*\"[^\"]*/arch/$arch\""
+
+    grep -qE "$pattern" "$board_toml" && return 0
+
+    local chip_path chip_toml
+    # Pulls the path out of each `chips/*` dependency the board declares.
+    for chip_path in $(grep -oE 'path[[:space:]]*=[[:space:]]*"[^"]*/chips/[^"]*"' "$board_toml" | sed -E 's/.*"(.*)"/\1/'); do
+        chip_toml="boards/$board/$chip_path/Cargo.toml"
+        [ -f "$chip_toml" ] && grep -qE "$pattern" "$chip_toml" && return 0
+    done
+    return 1
+}
+
+# Collected rather than printed as we go, so a failure partway through
+# (see below) leaves nothing on stdout instead of an incomplete board list
+# -- callers using `$(shell ...)` can't see a nonzero exit status, only
+# empty-vs-nonempty output.
+found_boards=""
+
+for arch in $(./tools/build/list_archs.sh); do
+    found=""
+    for board in "${boards[@]}"; do
+        if board_depends_on_arch "$board" "$arch"; then
+            found="$board"
+            break
+        fi
+    done
+    if [ -n "$found" ]; then
+        found_boards="$found_boards$found
+"
+        continue
+    fi
+
+    # No board uses this arch directly -- fine if another arch crate does
+    # (e.g. cortex-m, picked up by cortex-m4), since it then gets compiled,
+    # and so checked, as a side effect of building that arch's own board.
+    grep -qE "path[[:space:]]*=[[:space:]]*\"\.\./$arch\"" arch/*/Cargo.toml 2>/dev/null && continue
+
+    echo "error: no board or arch crate depends on arch/$arch" >&2
+    exit 1
+done
+
+printf '%s' "$found_boards" | sort -u