SY-3680: Fix Issues with Arc Channel Analysis

[emilbon99]

Issue Pull Request

Linear Issue

Fixes:

SY-3680
SY-3679

Description

Basic Readiness

• I have performed a self-review of my code.
• I have added relevant, automated tests to cover the changes.
• I have updated documentation to reflect the changes.

Greptile Overview

Greptile Summary

Fixed two critical Arc language bugs and one C++ error handling bug:

Core Fixes:

• SY-3679: Fixed stateful variables initialized from channels to store values instead of channel references by unwrapping channel types in analyzeStatefulVariable
• SY-3680: Fixed function reusability with channel configs by deep copying Channels when creating nodes, preventing shared state between multiple function invocations
• Out-of-bounds read: Fixed xerrors::Error::matches() to provide end iterator for both ranges, preventing undefined behavior when pattern is longer than error type
• Index out-of-bounds: Fixed ReadChannelValue() to check for empty MultiSeries before accessing last element

Test Coverage:
All fixes include comprehensive test coverage with regression tests, integration tests, and edge case validation.

UI Improvements:
Enhanced Arc editor UX by enabling scrollBeyondLastLine, repositioning controls to full width with gradient overlay, and removing problematic platform-specific font override.

Confidence Score: 5/5

• This PR is safe to merge with no identified issues
• All changes address specific bugs with proper fixes, include comprehensive test coverage, and follow established patterns in the codebase
• No files require special attention

Important Files Changed

Filename	Overview
arc/go/analyzer/statement/statement.go	Added type unwrapping for stateful variables initialized from channels to store values instead of channel references
arc/go/runtime/state/state.go	Fixed index out-of-bounds bug by checking for empty MultiSeries and using len() instead of Len() method
arc/go/text/analyze.go	Fixed channel aliasing bug by deep copying Channels when creating function nodes to prevent shared state
x/cpp/xerrors/errors.h	Fixed out-of-bounds read in matches() by providing end iterator to std::mismatch for both ranges

Sequence Diagram

sequenceDiagram
    participant User as Arc Program
    participant Analyzer as Statement Analyzer
    participant TextAnalyzer as Text Analyzer
    participant State as Runtime State
    participant WASM as WASM Runtime
    
    Note over User,WASM: Issue 1: Channel values in stateful vars
    User->>Analyzer: counter $= counter_ch
    Analyzer->>Analyzer: Check if varType is Chan
    Analyzer->>Analyzer: Unwrap() to get value type
    Analyzer->>User: Store value type (f32), not channel
    
    Note over User,WASM: Issue 2: Reusing functions with channel config
    User->>TextAnalyzer: increment{counter=counter_1}
    TextAnalyzer->>TextAnalyzer: sym.Channels.Copy()
    TextAnalyzer->>TextAnalyzer: slices.Clone(config)
    TextAnalyzer->>User: Create node with independent channels
    User->>TextAnalyzer: increment{counter=counter_2}
    TextAnalyzer->>TextAnalyzer: sym.Channels.Copy()
    TextAnalyzer->>User: Create separate node with own channels
    
    Note over User,WASM: Runtime: Reading channel values
    WASM->>State: ReadChannelValue(key)
    State->>State: Check if key exists
    State->>State: Check if len(ms.Series) > 0
    State->>State: Return ms.Series[len(ms.Series)-1]
    State->>WASM: Return last series safely
    
    Note over User,WASM: C++ Error Matching Fix
    User->>State: error.matches("long.pattern")
    State->>State: std::mismatch with both end iterators
    State->>User: Return false (no out-of-bounds)

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[greptile-apps]

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[sy-nico]

Can now use a function multiple times.

However, when attempting to initialize a variable with a channel value, there is no output on the counters

[sy-nico]

Chatted offline and left screenshots