Qt QML Code Review

A structured, read-only code review skill for Qt6 QML code that combines deterministic linting with parallel agent-driven deep analysis across six focused domains.

When to use this skill

• When the user mentions review-related tasks: "review", "check", "audit", "look over", "code review", "sanity check"
• Suggest running this skill before committing QML code
• When the user asks to validate Qt6 QML code quality

Scope detection

Detect the user's intended scope from their language:

Diff/commit scope (narrow)

Triggered by language like: "this commit", "these changes", "the diff", "what I changed", "my changes", "staged changes", "outstanding changes", "before I commit"

Action: Run git diff (unstaged) and git diff --cached (staged) to obtain the changeset. If the user says "this commit", use git diff HEAD~1..HEAD. Review only the changed lines plus sufficient surrounding context (±50 lines) for understanding. Only report issues found in the changed lines -- do not report issues in unchanged surrounding context.

Codebase scope (wide)

Triggered by language like: "review the codebase", "audit the project", "check the repository", "review src/", or when a specific file/directory path is given without commit language.

Action: Glob for *.qml files in the specified scope. Review all matched files.

Execution order

The review proceeds in three phases. Never skip a phase.

Phase 1: Deterministic linting (Python script)

Run the unified Python linter against the target files. Requires Python 3.6+ (no external dependencies). If Python is not available, warn the user and skip to Phase 1b.

python3 references/lint-scripts/qt_qml_lint.py <files...>
# If python3 is not found, fall back to:
python references/lint-scripts/qt_qml_lint.py <files...>

This single-pass scanner encodes all mechanically-checkable rules from the QML review checklist. It reads each file once and evaluates all rules per line, plus block-level structural checks. Output is deterministic and repeatable. The linter is authoritative -- do not second-guess its output.

Collect all output before proceeding.

Rule categories (47+ checks):

• IMP (Imports) -- ordering, versioning, redundancy, deprecation
• ORD (Ordering) -- QML attribute ordering convention
• BND (Bindings) -- property var, imperative =, Qt.binding style
• LAY (Layout) -- anchors/Layout mixing, sizing in layouts
• LDR (Loader) -- status guards, createComponent, createQmlObject
• DEL (Delegates) -- required properties, reuse safety, connect()
• STA (States) -- PropertyChanges syntax, transitions, StateGroup
• IMG (Images) -- sourceSize, asynchronous loading
• PRF (Performance) -- transparent rect, opacity, clip, layer
• STY (Style) -- id:root, camelCase, group notation
• SIG (Signals) -- Connections target, handler syntax
• ERR (Error/Security) -- hardcoded http://, non-portable paths
• JS (JavaScript) -- var/let/const, loose equality

Phase 1b: System qmllint (optional)

Attempt to run qmllint if available on the system. Detection order:

1. $QT_HOST_PATH/bin/qmllint
2. which qmllint / where qmllint
3. Skip if not found (warn user)

If found, run with JSON output:

qmllint --json - -I <import-paths> <files...>

Parse the JSON output and merge with Python linter findings. Deduplicate by file+line+issue. qmllint is authoritative for type- level checks (unresolved types, incompatible assignments, alias cycles). The Python linter is authoritative for style, ordering, and performance patterns that qmllint does not cover.

Phase 2: Agent-driven deep analysis (6 parallel agents)

Launch six focused review agents in parallel. Name each agent descriptively when launching (e.g. "Agent 1: Bindings & Properties") to provide progress visibility. Each agent has a tight scope and a specific checklist. Agents are READ-ONLY -- they must never edit or write files.

Tool-agnostic agent contract: Each agent described below is a self-contained review mission. In Claude Code, launch them as general-purpose subagents. In other tools, implement each as whatever subprocess, prompt chain, or analysis pass the tool supports. The key requirement is that each agent:

• Has read access to all source files in scope
• Can search/grep the codebase to trace symbols
• Reports findings in the structured format below
• Applies confidence thresholds: >80 = confirmed finding, 60-79 = investigation target (max 10 total across all agents), <60 = suppress
• Does NOT duplicate findings from Phase 1 lint output (pass lint output as context to each agent)

See Agent missions below for the six agents.

Phase 3: Consolidation and reporting

Merge lint script output, qmllint output (if available), and all agent findings. Deduplicate (same file+line+issue = one finding). Apply confidence scoring. Format the final report using the output format below.

Agent missions

Launch all six agents in parallel. Pass each agent:

1. The list of files in scope
2. The Phase 1 lint output (so they skip already-flagged issues)
3. The Phase 1b qmllint output if available
4. Their specific mission below

Each agent should read all files in scope, then focus on its assigned categories.

---

Agent 1: Bindings & Properties

Scope: Binding correctness, property types, alias chains, qualified lookup, binding loops.

Check for:

• Multi-cycle binding loops (A changes B via handler, B's binding updates A) -- runtime only detects single-cycle
• Property alias chains (alias to alias) where intermediate components may not be initialized
• Unqualified property access (bare someProperty instead of root.someProperty) -- complements qmllint unqualified warning with semantic context
• Qt.binding() closures capturing loop variables by reference (use let not var)
• pragma ComponentBehavior: Bound missing on files with delegates that access outer-scope ids
• Missing readonly on properties that are bound but never imperatively assigned

References: references/qt-qml-review-checklist.md sections 3 (Bindings & Properties)

---

Agent 2: Layout & Anchoring

Scope: Anchoring correctness, layout sizing, visual tree structure.

Check for:

• Anchoring to items with visible: false (resolve the target id, check its visible property)
• Anchoring across unrelated visual tree branches (not sharing a common parent)
• Items in Layouts using implicitWidth/implicitHeight bindings that could create feedback loops
• Missing Layout.fillWidth/Layout.fillHeight on items that should stretch
• Nested Layouts without clear sizing policy (ambiguous size negotiation)

References: references/qt-qml-review-checklist.md section 4 (Layout & Anchoring)

---

Agent 3: Component Loading & Lifecycle

Scope: Loader patterns, dynamic object creation, Connections lifecycle, C++ integration.

Check for:

• Component.createObject() return values not tracked or destroyed (memory leak)
• Loader switching between source and sourceComponent at runtime (unsupported)
• Image with dynamic/network source missing Image.status error handling
• Connections with dynamically-changing target not handling null target state
• Context properties (rootContext()->setContextProperty()) in C++ integration code
• Object ownership issues at QML/C++ boundary (parentless objects returned from invokable functions)

References: references/qt-qml-review-checklist.md sections 5 (Loader), 8 (Images), 13 (C++ Integration)

---

Agent 4: ListView & Delegate Correctness

Scope: Model-view patterns, delegate lifecycle, reuse safety, required properties.

Check for:

• Missing required property int index when index is used in a delegate that declares other required properties
• Delegate accessing model.roleName for roles not defined in the model's roleNames()
• Complex delegates (nested Repeaters, multiple Loaders, heavy bindings) that will degrade scroll performance
• currentIndex usage without guards for known Qt bugs (QTBUG-48633, QTBUG-93293)
• DelegateChooser patterns that could fail on non-QAbstractItemModel (choice made once at creation, not re-evaluated)
• Pooled delegates remaining visible (missing onPooled: visible = false pattern)

References: references/qt-qml-review-checklist.md section 6 (ListView & Delegates)

---

Agent 5: States, Transitions & Structure

Scope: State machine correctness, migration patterns, component structure.

Check for:

• PropertyChanges.restoreEntryValues surprises (properties reverting on state exit when developer expects them to persist)
• Binding.restoreMode mismatch from Qt 5 migration (default changed from RestoreNone to RestoreBindingOrValue)
• Deprecated Connections handler syntax (onFoo:) vs modern function onFoo() in migrated code
• QtGraphicalEffects imports that should be migrated to MultiEffect (Qt 6.5+)
• Top-level component states that should use StateGroup for reusability
• Missing from/to on transitions that could fire unexpectedly when new states are added

References: references/qt-qml-review-checklist.md sections 7 (States), 14 (Migration)

---

Agent 6: Performance & Code Quality

Scope: Performance anti-patterns, rendering cost, JavaScript quality, style consistency.

Check for:

• Expensive expressions in property bindings (function calls that should be cached as readonly property)
• QRegularExpression or complex computation inside loops
• Missing Text.PlainText when rich text is not needed (default textFormat incurs parsing overhead)
• font.preferShaping: false opportunity (when text shaping features are unused)
• Signals that communicate down (should be functions) or functions that communicate up (should be signals)
• Unnecessary id assignments on objects never referenced
• Custom properties scattered across items instead of consolidated in QtObject { id: privates }
• Singletons used for data (should use property injection for testability)
• Pointer handler opportunities (MouseArea that should be TapHandler/DragHandler for multi-touch)
• Reusable components with explicit width/height instead of implicitWidth/implicitHeight (prevents consumer resizing)
• parent used without null-check in delegates or Loader items (can be null during creation/destruction)
• Missing pragma ComponentBehavior: Bound on files with delegates that access outer-scope ids

References: references/qt-qml-review-checklist.md sections 9 (Performance), 10 (Style), 11 (Signals), 12 (JavaScript), 13 (C++ Integration)

---

Confidence scoring guidelines

Confidence	Meaning	Action
90-100	Certain: direct rule violation with full trace	Report as finding
80-89	High: rule violation confirmed but edge case possible	Report as finding
60-79	Medium: likely issue but cannot fully verify	Report as investigation target
<60	Low: suspicion only	Suppress entirely

Investigation targets are findings the agent believes are real but cannot fully verify. These are presented in a separate section for human verification. Maximum 10 investigation targets per report, prioritized by confidence within the 60-79 band.

Output format

Present the final report as follows. Use exactly this structure.

## QML Code Review Report

**Scope**: [diff: `git diff HEAD~1..HEAD` | files: <paths>]
**Files reviewed**: N
**Issues found**: N (M from lint, K from deep analysis)
**qmllint**: [ran / not available]

---

### Lint findings

For each lint finding:

#### [L-NNN] <Short title>
- **File**: `path/to/file.qml:42`
- **Rule**: <rule ID from checklist>
- **Finding**: <what the script detected>
- **Mitigation**: <what to do, in prose -- no code patches>

---

### Deep analysis findings

For each agent finding:

#### [D-NNN] <Short title>
- **File**: `path/to/file.qml:42`
- **Category**: <agent name: Bindings & Properties | Layout &
  Anchoring | Component Loading & Lifecycle | ListView &
  Delegates | States & Structure | Performance & Quality>
- **Confidence**: NN/100
- **Finding**: <description of the issue>
- **Trace**: <how the issue was confirmed -- which symbols were
  followed, what was checked>
- **Mitigation**: <what to do, in prose -- no code patches>

---

### Investigation targets (human verification needed)

Findings the agent identified but could not fully verify.
Maximum 10, sorted by confidence. These require human judgment.

For each investigation target:

#### [I-NNN] <Short title>
- **File**: `path/to/file.qml:42`
- **Category**: <agent name>
- **Confidence**: NN/100
- **Finding**: <what the agent suspects>
- **Unverified because**: <what the agent could not confirm>
- **How to verify**: <specific action for the reviewer>

---

### Summary

| Category | Lint | Deep | Investigate | Total |
|----------|------|------|-------------|-------|
| ...      | N    | N    | N           | N     |
| **Total**| **M**| **K**| **I**       | **N** |

Findings below confidence 60 are suppressed entirely.

References

The following reference files contain detailed checklists:

• references/qt-qml-review-checklist.md -- Complete QML review rules (lint + agent rules, always loaded)
• references/lint-scripts/qt_qml_lint.py -- Single-pass Python linter (runs all 47+ checks in <1s)

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