fix(rspec): skip JSON parsing for non-JSON output

[mcampbell]

Summary

Fixes #1506 — RTK emits a false [rtk] rspec: JSON parse failed warning whenever rspec runs with its default text formatter (no --format json).

• Add starts_with('{') guard in filter_rspec_output() so JSON parsing is only attempted on JSON-shaped output
• Remove the now-unreachable eprintln!() warning
• Add test test_filter_rspec_text_output_no_warning to document and lock in the fix

Root Cause

filter_rspec_output() unconditionally attempted serde_json::from_str on all rspec output. When rspec runs without --format json (the common case), output is plain text, which always fails the parse and emits:

[rtk] rspec: JSON parse failed (expected value at line 1 column 1), using text fallback

The fallback worked correctly, but the warning was noise.

Fix

// Only attempt JSON parsing if output looks like JSON (starts with '{')
if trimmed.starts_with('{') {
    if let Ok(rspec) = serde_json::from_str::<RspecOutput>(trimmed) {
        return build_rspec_summary(&rspec);
    }
    let stripped = strip_noise(output);
    if let Ok(rspec) = serde_json::from_str::<RspecOutput>(&stripped) {
        return build_rspec_summary(&rspec);
    }
    // fall through if JSON-shaped but unparseable
}
filter_rspec_text(&strip_noise(output))

Testing

• All 29 rspec unit tests pass
• New test verifies text output produces no warning and correct summary
• cargo clippy --all-targets clean
• cargo fmt --all -- --check clean

[pszymkowiak]

[w] wshm · Automated triage by AI

📊 Automated PR Analysis

🐛 Type	bug-fix
🟢 Risk	low

Summary

Fixes a false warning emitted when rspec runs with its default text formatter by adding a starts_with('{') guard before attempting JSON parsing in filter_rspec_output(). This eliminates the noisy [rtk] rspec: JSON parse failed message for non-JSON output while preserving correct fallback behavior.

Review Checklist

• Tests present
• Breaking change
• Docs updated

Linked issues: #1506

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Analyzed automatically by wshm · This is an automated analysis, not a human review.