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theme.meta-theme-color-mismatch

Rule ID: theme.meta-theme-color-mismatch Severity: WARN Category: theme Target Standards: HTML Living Standard Section 4.2.5 (The meta element), Web App Manifest & Mobile OS Theme Integration, WCAG 2.2 Success Criterion 1.4.11 (Non-text Contrast)

1. Overview & Core Invariant

Detects static meta theme-color tags lacking media prefers-color-scheme queries

Core Invariant:

"Meta theme-color elements must provide media query pairs (prefers-color-scheme: light/dark) to synchronize mobile browser chrome."

2. Technical Grounding & Engine Realities

Modern mobile browsers (Safari on iOS, Chrome on Android) color the operating system status bar and address bar based on the element in the document

.

When developers specify a single static theme-color without media queries (e.g. ):

  1. Blinding Address Bar: When the user toggles dark mode, the mobile address bar and status bar remain stark white, causing harsh visual glare.
  2. Inverted Chrome: When the page switches to dark background, white status bar text collapses against white browser chrome.

Charites enforces declaring media="(prefers-color-scheme: light)" and media="(prefers-color-scheme: dark)" pairs on all meta theme-color definitions.

3. Vulnerability & Risk Taxonomy

Risk Vector Severity Impact
Mobile Chrome Glare MEDIUM Mobile Safari and Chrome address bars blast high-brightness white chrome when the application is viewed in dark mode.
Status Bar Text Invisibility LOW OS status bar text (time, battery, Wi-Fi) becomes invisible due to poor contrast against unadapted address bar backgrounds.

4. Non-Compliant Code Patterns (Bad Examples)

ASTRO (Static theme-color meta tag in Astro layout):

<meta name="theme-color" content="#ffffff" />

TSX (Static theme-color in TSX Document head):

<meta name="theme-color" content="#09090b" />

5. Compliant Implementation Patterns (Good Examples)

ASTRO (Adaptive light/dark meta theme-color pair in Astro):

<>
  <meta name="theme-color" media="(prefers-color-scheme: light)" content="#ffffff" />
  <meta name="theme-color" media="(prefers-color-scheme: dark)" content="#09090b" />
</>

TSX (Adaptive meta theme-color pair in TSX):

<head>
  <meta name="theme-color" media="(prefers-color-scheme: light)" content="#ffffff" />
  <meta name="theme-color" media="(prefers-color-scheme: dark)" content="#09090b" />
</head>

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

This theme rule evaluates source templates against the project's design token graph:

flowchart TD
    Node["AST Node (Astro / TSX element)"] --> Extract["1. Extract Class Names (e.g. 'hover:bg-primary/10')"]
    Extract --> Strip["2. Strip Variants (hover:, dark:, sm:) -> 'bg-primary/10'"]
    Strip --> Split["3. Split Opacity Modifier -> Utility: 'bg-primary', Opacity: '/10'"]
    Split --> Convention["4. Query TokenConvention (Candidate: '--color-primary-light')"]
    Convention --> GraphQuery{"5. Check Token Graph (Does token exist in active scope?)"}
    GraphQuery -- "No (Banana Test)" --> Safe["Pass (Valid Custom / Untokenized Color)"]
    GraphQuery -- "Yes (Official Token Exists)" --> IgnoreCheck{"6. Check charites:ignore directive"}
    IgnoreCheck -- "Ignored" --> Safe
    IgnoreCheck -- "Not Ignored" --> Diag["7. Emit Diagnostic: theme.meta-theme-color-mismatch with Replacement Suggestion"]
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Step-by-Step Evaluation:

  1. AST Node Traversal: internal/analyzer streams JSX/Astro AST elements to the rule's Evaluate visitor.
  2. Variant Normalization: Strips responsive (sm:, md:), interaction state (hover:, focus:), and theme (dark:) prefixes to isolate the core utility class.
  3. Modifier Extraction: Parses utility segments and extracts slash opacity modifiers.
  4. Token Convention Resolution: Consults the TokenConvention adapter to determine the official semantic design token replacement candidate.
  5. Token Graph Verification (Banana Test): Queries token.Context to verify that the candidate token is declared in global.css or tokens.json within the element's scope. If not declared, the custom value is permitted without a false-positive diagnostic.
  6. Directive Suppression Check: Inspects preceding AST comments for charites:ignore theme.meta-theme-color-mismatch.
  7. Diagnostic Emission: Produces a structured diagnostic with line number, column span, and actionable replacement suggestion.

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/theme.meta-theme-color-mismatch/:

flowchart TD
    subgraph GoldenCorpus ["1-SSOT Tri-Corpus Test Matrix for theme.meta-theme-color-mismatch"]
        subgraph P ["Positive Corpus (tests/correctness/theme.meta-theme-color-mismatch/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/theme.meta-theme-color-mismatch/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/theme.meta-theme-color-mismatch/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.

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 theme.meta-theme-color-mismatch intentional exception -->
// charites:ignore theme.meta-theme-color-mismatch intentional exception

9. Configuration Reference (charites.yaml)

rules:
  theme.meta-theme-color-mismatch:
    severity: warn # error | warn | info | off

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