tools/devshell/contrib/g-build

#!/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
### Build Fuchsia and attempt to fix failures with Gemini.

## usage: fx g-build [BUILD_ARGS]...
##
## This command runs the standard 'fx build' with the provided arguments.
## If the build fails, it will invoke Gemini to diagnose and attempt to
## fix the build error.
##
## All arguments are passed directly to 'fx build'. See 'fx build --help' for details.

# Ensure FUCHSIA_FX_INVOKER is set for duration of script for tool analytics.
export FUCHSIA_FX_INVOKER=gemini
trap 'unset FUCHSIA_FX_INVOKER' EXIT

source "$(cd "$(dirname "${BASH_SOURCE[0]}")" >/dev/null 2>&1 && pwd)"/../lib/vars.sh || exit $?
SIGINT_EXIT_CODE=130 # Exit code for SIGINT (Ctrl+C)
MAX_ATTEMPTS=3

function fix_build_with_gemini {
  local -r build_output="$1"
  shift
  local -r gemini_prompt=$(cat <<EOF
The Fuchsia build failed. Your task is to diagnose and fix the build error.

**Output Requirements**
* Prefix output from "Implement" and "Summarize" with "[fx-gemini]".
* The output should be concise and suitable for CLI output.

**Workflow**
1.  **Analyze:**
    *   Examine the build error messages provided below to understand the root cause.
    *   Examine recent code changes using \`git log -p -1\` or \`git diff HEAD\` to see the latest modifications.
    *   Do not modify \`tools/devshell/contrib/g-build\` itself.
2.  **Plan:**
    *   Based on your analysis, formulate a clear plan to fix the issue.
3.  **Implement:**
    *   Edit only the files provided from the BUILD OUTPUT section.
    *   Do not edit any existing comments or code not relevant to the fix.
    *   Adhere to the existing coding style of the file(s) being modified.
4.  **Summarize:**
    *   Summarize the changes you made and exit the session.
    *   Do not run build commands. The calling script will re-run the build to verify your fix.

**BUILD OUTPUT**
${build_output}
EOF
)
  local GEMINI_ALLOWED_TOOLS="write_file,search_for_files_codesearch,code_editor,ShellTool(fx),ShellTool(ls),ShellTool(jiri),ShellTool(git diff),ShellTool(git log)"
  local -r jq_filter='if .type == "message" and .role == "assistant" then
      .content
    elif .type == "tool_use" then
      "[fx-gemini] Using tool [\(.tool_name)]" +
      (if .tool_name == "write_file" or .tool_name == "read_file" then
        ": \(.parameters.file_path // "Unknown file")"
      elif .parameters.description then
        ": \(.parameters.description)"
      else
        ""
      end)
    else
      empty
    end | select(length > 0)
  '
  set -o pipefail
  /google/bin/releases/gemini-cli/tools/gemini \
    -m gemini-2.5-flash \
    -p "${gemini_prompt}" \
    --allowed-tools "${GEMINI_ALLOWED_TOOLS}" \
    --output-format stream-json 2>&1 | \
  grep --line-buffered '^\{' | \
  fx-command-run jq --unbuffered -r "${jq_filter}" >&2
  local gemini_status=${PIPESTATUS[0]}
  set +o pipefail

  if [[ "${gemini_status}" -ne 0 ]]; then
      echo >&2 "[fx-gemini] Gemini process failed with status ${gemini_status}."
  fi

  if [[ "${gemini_status}" -eq 0 ]]; then
      echo >&2 "[fx-gemini] Ensuring trailing newlines in modified files..."
      git diff --name-only HEAD | while read -r line; do
          abs_path="$(git rev-parse --show-toplevel)/$line"
          if [[ -f "$abs_path" ]] && [[ -n "$(tail -c 1 "$abs_path")" ]]; then
              echo "" >> "$abs_path"
              echo >&2 "[fx-gemini] Added missing newline to: $line"
          fi
      done
  fi

}

set +e
BUILD_OUTPUT_FILE=$(mktemp)
trap 'rm -f "${BUILD_OUTPUT_FILE}"' EXIT

fx-command-run build "$@" 2>&1 | tee "${BUILD_OUTPUT_FILE}"
BUILD_STATUS=${PIPESTATUS[0]}
BUILD_OUTPUT=$(<"${BUILD_OUTPUT_FILE}")
set -e

# If the build failed, attempt to fix it with Gemini (up to 3 times)
if [[ "${BUILD_STATUS}" -ne 0 && "${BUILD_STATUS}" -ne "${SIGINT_EXIT_CODE}" ]]; then
  for i in $(seq 1 $MAX_ATTEMPTS)
  do
    echo >&2 "[fx-gemini] Build failed. Attempting fix $i of $MAX_ATTEMPTS with Gemini..."
    if fix_build_with_gemini "${BUILD_OUTPUT}" "$@"; then
      # Re-run the build to check if the fix was successful
      echo >&2 "[fx-gemini] Re-running build to verify fix..."
      set +e
      # BUILD_OUTPUT_FILE is still the one from the initial mktemp
      fx-command-run build -q "$@" 2>&1 | tee "${BUILD_OUTPUT_FILE}"
      new_build_status=${PIPESTATUS[0]}
      BUILD_OUTPUT=$(<"${BUILD_OUTPUT_FILE}") # Update BUILD_OUTPUT for the next loop
      set -e
      if [[ "${new_build_status}" -eq 0 ]]; then
          echo >&2 "[fx-gemini] Gemini successfully fixed the build on attempt $i."
          exit 0
      fi
    fi
  done
  echo >&2 "[fx-gemini] Gemini failed to fix the build after $MAX_ATTEMPTS attempts."
  exit 1
fi

exit ${BUILD_STATUS}