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theme.split-theme-state

Rule ID: theme.split-theme-state Severity: WARN Category: theme Target Standards: Design System Single Source of Truth (SSOT) Architecture, React State Management Best Practices (Context & Hooks), WCAG 2.2 Predictable Navigation & Consistency

1. Overview & Core Invariant

Detects ad-hoc direct access to theme state via localStorage outside ThemeProvider

Core Invariant:

"Component UI state must consume theme through a unified ThemeProvider context or custom hook, never querying localStorage directly in component bodies or handlers."

2. Technical Grounding & Engine Realities

When developers directly access or mutate localStorage.getItem('theme') or localStorage.theme in scattered components:

  1. Fragmented State: Component A reads localStorage while Component B listens to React Context, causing disparate parts of the UI to display inconsistent themes.
  2. Missing Reactivity: Updates directly to localStorage do not trigger React or framework re-renders across sibling components.
  3. Testability Breakdown: Components cannot be unit tested or rendered in isolation without mocking global browser APIs.

Charites enforces routing all theme state access through a unified Theme Provider / useTheme hook, permitting direct localStorage access only in root

bootstrap scripts.

3. Vulnerability & Risk Taxonomy

Risk Vector Severity Impact
Theme Desynchronization Across UI MEDIUM Different page regions display discordant color schemes due to uncoordinated local state reads.
Broken Component Reactivity MEDIUM Theme switches fail to re-render affected components without a full browser page refresh.

4. Non-Compliant Code Patterns (Bad Examples)

TSX (Direct localStorage mutation in button onClick handler):

<button onClick={() => localStorage.setItem('theme', 'dark')}>Toggle</button>

ASTRO (Direct localStorage inspection in Astro component body):

<div data-theme={localStorage.getItem('theme')}>Container</div>

5. Compliant Implementation Patterns (Good Examples)

TSX (Using unified useTheme hook from ThemeProvider):

const { theme, setTheme } = useTheme();
<button onClick={() => setTheme(theme === 'dark' ? 'light' : 'dark')}>Toggle</button>

ASTRO (Permitted inline bootstrap script inside root ):

<head>
  <script is:inline>
    const theme = localStorage.getItem('theme') || 'light';
    document.documentElement.classList.toggle('dark', theme === 'dark');
  </script>
</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.split-theme-state 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.split-theme-state.
  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.split-theme-state/:

flowchart TD
    subgraph GoldenCorpus ["1-SSOT Tri-Corpus Test Matrix for theme.split-theme-state"]
        subgraph P ["Positive Corpus (tests/correctness/theme.split-theme-state/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.split-theme-state/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.split-theme-state/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.split-theme-state intentional exception -->
// charites:ignore theme.split-theme-state intentional exception

9. Configuration Reference (charites.yaml)

rules:
  theme.split-theme-state:
    severity: warn # error | warn | info | off

Charites Wiki

Rule Categories

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Cls (16 rules)
Design (1 rules)
Ergonomy (5 rules)
Inp (16 rules)
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Performance (16 rules)
Pwa (10 rules)
Responsive (18 rules)
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Theme (32 rules)
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