tools/devshell/contrib/fetch-toolchain

#!/bin/bash
# Copyright 2026 The Fuchsia Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

#### CATEGORY=Build
#### PREBUILTS=${PREBUILT_CAS} ${PREBUILT_JQ}
### Download toolchain from CAS and print instructions

## usage: fx fetch-toolchain <CAS_DIGEST>
##
## Downloads the toolchain specified by <CAS_DIGEST> to $FUCHSIA_DIR/local/toolchain/<CAS_DIGEST>.
## Prints instructions for how to use it with `fx set` or in `args.gn`.

readonly SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" >/dev/null 2>&1 && pwd)"
source "$SCRIPT_DIR/../lib/vars.sh" || exit $?

fx-config-read

set -e

function usage() {
    echo "Usage: fx fetch-toolchain <CAS_DIGEST>"
    echo "       fx fetch-toolchain --canary"
    echo ""
    echo "Options:"
    echo "  --canary        Automatically retrieve the latest canary CAS digest."
    echo ""
    echo "Downloads the toolchain specified by <CAS_DIGEST> to \$FUCHSIA_DIR/local/toolchain/<CAS_DIGEST>."
    echo "Prints instructions for how to use it with \`fx set\` or in \`args.gn\`."
    echo ""
}

if [[ $# -lt 1 ]]; then
    usage
    echo "ERROR: Too few arguments. At least one argument is required."
    exit 1
fi

if [[ "$1" == "--help" || "$1" == "-h" ]]; then
    usage
    exit 0
fi

DIGEST=""

if [[ "$1" == "--canary" ]]; then
    if ! bb auth-info >/dev/null 2>&1; then
        echo "ERROR: Not authenticated to buildbucket."
        echo "Please run 'bb auth-login' and try again."
        exit 1
    fi

    readonly BUILDER="fuchsia/global.ci/clang_toolchain.ci.core.x64-debug-tot-build_only"
    readonly JQ_QUERY='first(.input.properties.["$recipe_engine/scheduler"].triggers[].buildbucket.properties.["$fuchsia/checkout"].clang_toolchain.cas_digest)'

    echo "Resolving latest canary digest..."
    DIGEST=$(bb ls -fields input -n 1 -json "${BUILDER}" | jq -r "${JQ_QUERY}")

    if [[ -z "$DIGEST" || "$DIGEST" == "null" ]]; then
        echo "ERROR: Failed to resolve canary digest."
        exit 1
    fi
    echo "Resolved canary digest: ${DIGEST}"
else
    DIGEST="$1"
fi

TARGET_DIR="${FUCHSIA_DIR}/local/toolchain/${DIGEST}"

if [[ -d "${TARGET_DIR}" ]] && [[ -n "$(ls -A "${TARGET_DIR}" 2>/dev/null)" ]]; then
    echo "Toolchain already exists at ${TARGET_DIR}. Skipping download."
else
    echo "Creating directory ${TARGET_DIR}"
    mkdir -p "${TARGET_DIR}"

    echo "Downloading toolchain from CAS..."
    "${FUCHSIA_DIR}/prebuilt/tools/cas/cas" download -cas-instance chromium-swarm -digest "${DIGEST}" -dir "${TARGET_DIR}"
fi

echo ""
echo "Toolchain downloaded to ${TARGET_DIR}"
echo ""
echo "To use this toolchain with fx set:"
echo "  fx set <board>.<product> --args=clang_prefix=\"\${FUCHSIA_DIR}/local/toolchain/${DIGEST}/bin\""
echo ""
echo "To use this toolchain in args.gn (e.g., out/default/args.gn):"
echo "  clang_prefix = \"//local/toolchain/${DIGEST}/bin\""
echo ""