pwa.icon maskable missing

pwa.icon-maskable-missing

Rule ID: pwa.icon-maskable-missing Severity: WARN Category: pwa Target Standards: W3C Web App Manifest Specification (Adaptive Icon Masking), Google Android Maskable Icons Specification, Android Oreo+ Adaptive Launcher Icon Architecture

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1. Overview & Core Invariant

Warns when a Web App Manifest defines icons but none has purpose: 'maskable' for Android adaptive launcher icons

Core Invariant:

"When a Web App Manifest defines icons, at least one icon must declare 'purpose: "maskable"' to prevent Android launcher letterboxing."

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2. Technical Grounding & Engine Realities

Starting in Android 8.0 Oreo, native device launchers crop application icons according to user-selected device masks (circles, squircles, rounded rectangles).

When a PWA provides only standard icons (purpose: 'any' or omitted purpose), modern Android launchers place the icon inside a small white square box (letterboxing) to fit the mask. This disrupts the visual consistency of native mobile app trays.

Providing at least one icon with 'purpose: "maskable"' (with an appropriate safe zone margin) ensures the launcher can scale and mask the icon seamlessly to fill the full shape.

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3. Vulnerability & Risk Taxonomy

Risk Vector	Severity	Impact
Letterboxed Android Launcher Icons	MEDIUM	PWA icon appears inside an awkward white square box on Android device home screens.
Degraded Native Visual Immersion	LOW	Breaks aesthetic parity with native Android apps installed from Google Play.

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4. Non-Compliant Code Patterns (Bad Examples)

TSX (Manifest defines icons without any maskable purpose):

<script type="application/manifest+json">
  {JSON.stringify({
    name: "Desa Digital",
    start_url: "/",
    display: "standalone",
    icons: [
      { src: "/icon-512.png", sizes: "512x512", type: "image/png" }
    ]
  })}
</script>

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5. Compliant Implementation Patterns (Good Examples)

TSX (Manifest includes an adaptive icon with purpose: maskable):

<script type="application/manifest+json">
  {JSON.stringify({
    name: "Desa Digital",
    start_url: "/",
    display: "standalone",
    icons: [
      { src: "/icon-512.png", sizes: "512x512", type: "image/png" },
      { src: "/icon-512-maskable.png", sizes: "512x512", type: "image/png", purpose: "maskable" }
    ]
  })}
</script>

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6. Detection & Verification Pipeline (How The Rule Evaluates Code)

This rule evaluates source code through the standard AST inspection pipeline:

flowchart TD
    Node["AST Node (Astro / TSX element)"] --> Inspect["1. Inspect Element & Attributes"]
    Inspect --> Invariant{"2. Evaluate Rule Invariant"}
    Invariant -- "Compliant" --> Safe["Pass"]
    Invariant -- "Non-Compliant" --> IgnoreCheck{"3. Check charites:ignore directive"}
    IgnoreCheck -- "Ignored" --> Safe
    IgnoreCheck -- "Not Ignored" --> Diag["4. Emit Diagnostic: pwa.icon-maskable-missing"]

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Step-by-Step Evaluation:

1. AST Traversal: Visits normalized ir.Node structures during AST streaming.
2. Invariant Check: Compares node attributes against rule invariants.
3. Directive Suppression Check: Honors inline charites:ignore pwa.icon-maskable-missing directives.
4. Diagnostic Emission: Emits compiler-grade diagnostic on invariant violation.

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7. Verification & Test Harness (How The Test Works: 1-SSOT Tri-Corpus)

This rule is rigorously tested and validated across the canonical 1-SSOT Tri-Corpus in tests/correctness/pwa.icon-maskable-missing/:

flowchart TD
    subgraph GoldenCorpus ["1-SSOT Tri-Corpus Test Matrix for pwa.icon-maskable-missing"]
        subgraph P ["Positive Corpus (tests/correctness/pwa.icon-maskable-missing/positive/)"]
            P1["P1: Obvious Direct Violation"]
            P2["P2: Indirect / Variant Concatenation"]
            P3["P3: Helper / clsx / cn Wrapper"]
            P4["P4: Deeply Nested Elements"]
            P5["P5: Aliased Imports / Re-exports"]
        end
        subgraph N ["Negative Corpus (tests/correctness/pwa.icon-maskable-missing/negative/)"]
            N1["N1: Valid Design Tokens"]
            N2["N2: Explicit charites:ignore Directive"]
            N3["N3: Third-Party / Vendor Components"]
            N4["N4: Clean Semantic HTML"]
            N5["N5: Untokenized Custom Values (Banana Test)"]
        end
        subgraph A ["Adversarial Corpus (tests/correctness/pwa.icon-maskable-missing/adversarial/)"]
            A1["A1: Template Literal Interpolations"]
            A2["A2: Ternary Conditional Expressions"]
            A3["A3: Spread Properties & Dynamic Overrides"]
            A4["A4: Dynamic Object Class Syntax"]
            A5["A5: Shadowed Variable Identifiers"]
            A6["A6: Nested Closures & HOC Wrappers"]
            A7["A7: Obfuscated Classes & Cyclic Tokens"]
        end
    end

    P --> TestRunner["Automated Runner (rule_test.go)"]
    N --> TestRunner
    A --> TestRunner
    TestRunner --> Gates["Quality Gates: Zero Panic, Zero False-Positive, Zero Bypass"]

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• Positive Fixtures (P1-P5): Verified to trigger diagnostics at exact lines and column spans.
• Negative Fixtures (N1-N5): Verified to produce zero diagnostics on valid tokens and legitimate exemptions.
• Adversarial Fixtures (A1-A7): Verified to prevent evasion across dynamic expressions, string interpolations, and cyclic references.

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8. How to Suppress (Ignore Directives)

If this pattern is required for an intentional exception, suppress the diagnostic using the canonical Charites Rule ID:

<!-- charites:ignore pwa.icon-maskable-missing intentional exception -->

// charites:ignore pwa.icon-maskable-missing intentional exception

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9. Configuration Reference (charites.yaml)

rules:
  pwa.icon-maskable-missing:
    severity: warn # error | warn | info | off