Add parser coverage enforcement at 84% threshold

[rtfeldman]

Summary

• Add parser coverage enforcement at 84% minimum threshold
• Coverage runs in a separate workflow that doesn't block main CI
• Coverage runs on macOS ARM where kcov works correctly

Technical Details

• kcov uses LLDB on macOS (works with Zig binaries)
• kcov's ptrace-based approach on Linux doesn't work with Zig binaries (reports 0%)
• Coverage workflow runs in parallel with main CI
• Coverage takes ~5 hours but doesn't block CI completion
• Coverage reports are uploaded as artifacts

Test plan

• zig build coverage passes locally with 84.69% coverage
• Main CI passes without being blocked by coverage
• Coverage workflow created and configured

🤖 Generated with Claude Code

[diffray-bot]

Changes Summary

This PR adds code coverage enforcement to the parser build system with an 84% minimum threshold, prevents coverage regression, and adds snapshot tests for operators (pizza |>, caret ^) and malformed number/string error cases.

Type: mixed

Components Affected: Build system (build.zig), Parser source documentation (NodeStore.zig, tokenize.zig), Test suite (snapshot tests)

Files Changed

File	Summary	Change	Impact
/tmp/workspace/build.zig	Add MIN_COVERAGE_PERCENT constant (84%), modify parseCoverageJson() to return f64, add coverage validation logic with meaningful error messages, and configure kcov to exclude HTML.zig and debug statements.	✏️	🔴
/tmp/workspace/src/parse/NodeStore.zig	Add documentation comment explaining that the debug function is excluded from coverage measurement.	✏️	🟢
/tmp/workspace/src/parse/tokenize.zig	Add two documentation comments explaining debug output blocks are excluded from coverage.	✏️	🟢
...orkspace/test/snapshots/parse_pizza_operator.md	Add snapshot test for pizza operator (	>) parsing and precedence handling.	➕
...orkspace/test/snapshots/parse_caret_operator.md	Add snapshot test for caret operator (^) parsing and right-associativity.	➕	🟢
...test/snapshots/parse_malformed_binary_number.md	Add snapshot test for error handling of malformed binary numbers (0b without digits).	➕	🟢
...ce/test/snapshots/parse_malformed_hex_number.md	Add snapshot test for error handling of malformed hex numbers (0x without digits).	➕	🟢
.../test/snapshots/parse_malformed_octal_number.md	Add snapshot test for error handling of malformed octal numbers (0o without digits).	➕	🟢
...rkspace/test/snapshots/parse_unclosed_string.md	Add snapshot test for error handling of unclosed string literals.	➕	🟢

Architecture Impact

• New Patterns: Coverage-driven development enforcement via build system, Snapshot testing for parser behavior validation
• Coupling: Coverage measurement is now tightly coupled to the build process - any parser changes must maintain or improve test coverage.
• Breaking Changes: Build will fail if parser code coverage drops below 84% - developers cannot merge coverage-reducing changes

Risk Areas: Coverage threshold is hardcoded - increasing it requires code changes, Excludes debug statements which may hide untested error paths in production debugging code, HTML.zig exclusion assumes it's truly a visualization-only utility with no critical logic

Suggestions

• Consider making MIN_COVERAGE_PERCENT configurable via build parameter for flexibility
• Document the rationale for excluding HTML.zig and std.debug.* from coverage
• Verify that snapshot tests are comprehensive enough to cover the major operators and error cases

_{Full review in progress... | Powered by diffray}

[rtfeldman]

Superseded by #8878 which includes additional fixes for coverage enforcement

[rtfeldman]

Closing in favor of #8864