Bazel Build System Management Skill

Manage and analyze Bazel workspaces, build targets, dependencies, and caching.

MANDATORY: Discovery-First Pattern

Always check current Bazel workspace and build configuration before modifying targets.

Phase 1: Discovery

#!/bin/bash

echo "=== Workspace Configuration ==="
cat WORKSPACE 2>/dev/null | head -20 || cat WORKSPACE.bazel 2>/dev/null | head -20
cat MODULE.bazel 2>/dev/null | head -20

echo ""
echo "=== .bazelrc Configuration ==="
cat .bazelrc 2>/dev/null | head -15

echo ""
echo "=== Bazel Version ==="
bazel version 2>/dev/null | head -3

echo ""
echo "=== Top-Level Packages ==="
ls */BUILD */BUILD.bazel 2>/dev/null | head -15

Phase 2: Analysis

#!/bin/bash

echo "=== All Build Targets ==="
bazel query '//...' 2>/dev/null | head -20

echo ""
echo "=== Target Types Summary ==="
bazel query '//...' --output=label_kind 2>/dev/null | awk '{print $1}' | sort | uniq -c | sort -rn | head -10

echo ""
echo "=== External Dependencies ==="
bazel query 'deps(//...)' --output=label 2>/dev/null | grep '@' | sed 's|//.*||' | sort -u | head -10

Output Rules

• TOKEN EFFICIENCY: Target <=50 lines per output
• Summarize target counts by rule type
• List external dependencies concisely
• Report build timing from profiles

Common Operations

Dependency Graph Query

#!/bin/bash
TARGET="${1:?Target required (e.g., //src:main)}"
echo "=== Dependencies for $TARGET ==="
bazel query "deps($TARGET)" --output=label 2>/dev/null | head -20
echo ""
echo "=== Reverse Dependencies ==="
bazel query "rdeps(//..., $TARGET)" --output=label 2>/dev/null | head -10

Build Performance Profile

#!/bin/bash
echo "=== Build Profile ==="
bazel build //... --profile=/tmp/bazel_profile.json 2>/dev/null
cat /tmp/bazel_profile.json 2>/dev/null | jq '{
  total_duration: .traceEvents[-1].ts,
  critical_path: [.traceEvents[] | select(.cat == "critical path") | .name] | .[0:5]
}' 2>/dev/null

Safety Rules

• Never run bazel clean --expunge without understanding the full rebuild cost
• Test BUILD file changes with bazel build --check_visibility before committing
• Remote execution credentials must be stored in CI secrets, not in .bazelrc
• Review external dependency updates carefully -- Bazel pins exact versions for reproducibility

Output Format

Present results as a structured report:

Managing Bazel Report
═════════════════════
Resources discovered: [count]

Resource       Status    Key Metric    Issues
──────────────────────────────────────────────
[name]         [ok/warn] [value]       [findings]

Summary: [total] resources | [ok] healthy | [warn] warnings | [crit] critical
Action Items: [list of prioritized findings]

Target ≤50 lines of output. Use tables for multi-resource comparisons.

Anti-Hallucination Rules

1. NEVER assume resource names — always discover via CLI/API in Phase 1 before referencing in Phase 2.
2. NEVER fabricate metric names or dimensions — verify against the service documentation or --help output.
3. NEVER mix CLI commands between service versions — confirm which version/API you are targeting.
4. ALWAYS use the discovery → verify → analyze chain — every resource referenced must have been discovered first.
5. ALWAYS handle empty results gracefully — an empty response is valid data, not an error to retry.

Counter-Rationalizations

Shortcut	Counter	Why
"I'll skip discovery and check known resources"	Always run Phase 1 discovery first	Resource names change, new resources appear — assumed names cause errors
"The user only asked for a quick check"	Follow the full discovery → analysis flow	Quick checks miss critical issues; structured analysis catches silent failures
"Default configuration is probably fine"	Audit configuration explicitly	Defaults often leave logging, security, and optimization features disabled
"Metrics aren't needed for this"	Always check relevant metrics when available	API/CLI responses show current state; metrics reveal trends and intermittent issues
"I don't have access to that"	Try the command and report the actual error	Assumed permission failures prevent useful investigation; actual errors are informative