Triage Process

When working on a category of CTS tests, follow this systematic process to identify issues, prioritize fixes, and document findings.

Step 0: Divide Into Manageable Chunks

List all the tests matching a selector:

cargo xtask cts -- --list 'webgpu:api,validation,*' 2>&1 | wc -l

If there is a reasonable number of tests matching the selector (less than a couple hundred or so, but this isn't a hard cutoff), then you can proceed with triage. Otherwise, make a list of more detailed wildcards that match fewer tests, verify that each wildcard matches a reasonable number of tests, and triage each wildcard separately.

Step 1: Get Overall Statistics

Run the full test suite for the category to understand the scope:

cargo xtask cts 'webgpu:api,validation,category:*' 2>&1 | grep -E "(Summary|Passed|Failed)" | tail -5

This gives you the pass rate and number of failures. Document this as your baseline.

Step 2: Identify Test Subcategories

Review the output from the running the CTS (with or without --list) to identify any subcategories that may exist within the suite being analyzed. Subcategories typically have an additional :- or ,-delimited word in the test name. Running tests by subcategory may be more manageable than running with the entire suite at once or running individual tests.

Step 3: Run Each Subcategory

Test each subcategory individually to identify which ones are passing vs failing:

cargo xtask cts 'webgpu:api,validation,category:subcategory:*' 2>&1 | grep -E "(Passed|Failed|Skipped)" | tail -3

Track the pass rate for each subcategory. This helps you identify:

• What's already working (don't break it!)
• Where the failures are concentrated
• Which issues affect multiple categories

Step 4: Analyze Failure Patterns

For failing subcategories, look at what tests are failing:

cargo xtask cts 'webgpu:api,validation,category:subcategory:*' 2>&1 | grep "\[fail\]" | head -20

Look for patterns:

• Format-specific failures: May indicate missing format capability checks
• Parameter-specific failures: Validation missing for specific parameter combinations

Step 5: Examine Specific Failures

Pick a representative failing test and run it individually to see the error:

cargo xtask cts 'webgpu:api,validation,category:subcategory:specific_test' 2>&1 | tail -30

Look for:

• "EXPECTATION FAILED: DID NOT REJECT": wgpu is accepting invalid input (validation gap)
• "Validation succeeded unexpectedly": Similar to above
• "Unexpected validation error occurred": wgpu is rejecting valid input
• Error message content: Tells you what validation is triggering or missing

Step 6: Check CTS Test Source

To understand what the test expects, read the TypeScript source:

grep -A 40 "test_name" cts/src/webgpu/api/validation/path/file.spec.ts

The test source shows:

• What configurations are being tested
• What the expected behavior is (pass/fail)
• The validation rules from the WebGPU spec
• Comments explaining the rationale

Step 7: Categorize Issues

Group failures into categories:

High Priority - Validation Gaps:

• wgpu accepts invalid configurations that should fail
• Security or correctness implications
• Example: Accepting wrong texture formats, missing aspect checks

Medium Priority - Spec Compliance:

• Edge cases not handled correctly
• Optional field validation issues
• Example: depthCompare optional field handling

Low Priority - Minor Gaps:

• Less common scenarios
• Limited real-world impact
• Example: Depth bias with non-triangle topologies

Known Issues - Skip:

• Known failure patterns (documented in Common Patterns below)
• Track count but don't try to fix

Step 8: Identify Root Causes

For validation gaps, find where validation should happen:

1. Search for existing validation:

   grep -n "relevant_keyword" wgpu-core/src/device/resource.rs
   

2. Look for render/compute pipeline creation:

   • Render pipeline: wgpu-core/src/device/resource.rs around create_render_pipeline
   • Compute pipeline: Similar location
   • Look for existing validation patterns you can follow

3. Check for helper functions:

   grep "fn is_" wgpu-types/src/texture/format.rs
   

4. Find error enums:

   grep "pub enum.*Error" wgpu-core/src/pipeline.rs
   

Step 9: Implement Fixes

When implementing fixes:

1. Add error variants if needed (in wgpu-core/src/pipeline.rs)
2. Add helper methods (in wgpu-types if checking properties)
3. Add validation checks (in wgpu-core/src/device/resource.rs)
4. Test the fix with specific failing tests
5. Run full subcategory to verify all related tests pass
6. Check you didn't break passing tests

Step 10: Document Findings

Create or update a triage document (e.g., category_triage.md).

Do not write information about changes you have made to the triage document. Only capture the state of the tests and any investigation into open issues.

# Category CTS Tests - Triage Report

**Overall Status:** XP/YF/ZS (%/%/%)

## Passing Sub-suites ✅

[List sub-suites that have no failures (all pass or skip)]

## Remaining Issues ⚠️

[List sub-suites that have failures and if it can be stated concisely, a summary of the issue]

## Issue Detail

[List detail of any investigation into failures. Do not go into detail about passed suites, just list the failures.]

### 1. title, e.g. a distinguishing word from the test selector

**Test selector:** `webgpu:api,validation,render_pipeline,depth_stencil_state:format:*`
**What it tests:** [Description]
**Example failure:**
[a selector for a single failing test, e.g.:]

```
webgpu:api,validation,render_pipeline,depth_stencil_state:depthCompare_optional:isAsync=false;format="stencil8"
```

**Error:**
[error message from the failing tests, e.g.:]

```
Unexpected validation error occurred: Depth/stencil state is invalid:
Format Stencil8 does not have a depth aspect, but depth test/write is enabled
```

**Root cause:**
[Your analysis of the root cause. Do not speculate. Only include the results of specific investigation you have done.]
The validation is triggering incorrectly. When `depthCompare` is undefined/missing in JavaScript, it's getting translated to a default value that makes `is_depth_enabled()` return true, even for stencil-only formats.

**Fix needed:**
[Your proposed fix. Again, do not speculate. Only state the fix if it is obvious from the root cause analysis, or if you have done specific investigation into how to fix it.]

### 2. title

[repeat as needed for additional issues]

Step 11: Update CTS Result Lists

The result lists have these purposes:

• cts_runner/test.lst contains sets of tests with no failures. It is not an exhaustive list of passing sets of tests.
• cts_runner/fail.lst contains sets of tests with failures. A comment can record the pass rate, especially when the pass rate is high.
• cts_runner/skip.lst contains sets of tests in which at least 90% of the tests are skipped.

If you fix a set of tests, add it to cts_runner/test.lst only when all of its tests pass or skip. Do not add a set of tests that has any failures.

Use wildcards to minimize the number of selectors:

webgpu:api,validation,category:subcategory:isAsync=false;*

Use a higher-level wildcard only when all tests that it matches belong in the same result list. Do not use a wildcard that also matches tests from another result list.

Keep the selectors in the order that the lst_files_are_sorted integration test requires. This rule also applies to selectors in comments.

Step 12: Verify and Build

Before finishing:

# Format code
cargo fmt

# Check for errors
cargo clippy --tests

# Build to ensure no compilation errors
cargo build

# Run the tests you added to test.lst
cargo xtask cts 'webgpu:api,validation,category:subcategory:isAsync=false;*'

Common Patterns

If the user asked to investigate a failure, and the cause of the failure is noted here with "do not attempt to fix", then stop and ask the user before attempting to fix.

Pattern: Format-specific failures

• Check if format validation is missing
• Look for is_depth_stencil_format(), is_color_format() etc.
• May need to add format capability checks

Pattern: Aspect-related failures

• Check if code validates format aspects (DEPTH, STENCIL, COLOR)
• Use hal::FormatAspects::from(format) to check
• Validate operations match available aspects

Pattern: Optional field failures

• May be WebGPU optional field semantics issue
• Check if undefined in JS becomes a default value in Rust
• May need to distinguish "not set" from "set to default"

Pattern: Atomics accepted incorrectly

• Naga allows referencing an atomic directly in an expression
• Should only allow accessing via atomicLoad, atomicStore, etc.
• Only investigate as necessary to confirm this is the issue. Do not attempt to fix. Refer user to https://github.com/gfx-rs/wgpu/issues/5474.

Pattern: Error reporting for destroyed resources

• Tests that check for validation errors when a destroyed resource is used. wgpu often reports these errors later than WebGPU requires, causing the tests to fail.
• wgpu may report these errors earlier than it should, causing the test to fail with an unexpected validation error.
• Look for:
  • Tests with state="destroyed" parameter
  • Tests checking that operations on destroyed buffers or textures should fail
• Example failing tests:
  • webgpu:api,validation,encoding,cmds,compute_pass:indirect_dispatch_buffer_state: with state="destroyed" subcases
• Only investigate as necessary to confirm this is the issue. Do not attempt to fix. Refer user to https://github.com/gfx-rs/wgpu/issues/7881.

Tips

• Start with high-impact fixes: Validation gaps with security implications
• Look for existing patterns: Other validation code shows the style
• Test incrementally: Fix one category at a time, verify it works
• Document as you go: Don't wait until the end to write the triage
• Ask for clarification: If test expectations are unclear, check the WebGPU spec or test source
• Track your progress: Update pass rates as you fix issues