Allow opt-out of sitemap inclusion

[masenf]

Pass context={"sitemap": None} to app.add_page to exclude the page from the generated sitemap.

[codspeed-hq]

Merging this PR will not alter performance

Summary

✅ 8 untouched benchmarks

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_{Comparing masenf/sitemap-opt-out (2135a47) with main (89f3a27)}

[greptile-apps]

Greptile Summary

Added opt-out functionality for sitemap generation by allowing pages to pass context={"sitemap": None} to app.add_page. The implementation properly handles type narrowing by checking for explicit None values before processing sitemap configuration, maintaining backward compatibility with existing pages that don't specify sitemap configuration.

• Updated type annotation for sitemap_config from SitemapLinkConfiguration to SitemapLinkConfiguration | None to allow None values
• Added early return when sitemap_config is None to exclude pages from sitemap generation
• Type safety is maintained through Python's type narrowing after the None check
• Backward compatible: pages without sitemap context (context={}) or with empty sitemap config (context={"sitemap": {}}) continue to be included in the sitemap with default settings
• Comprehensive test case validates both opt-out and default inclusion behaviors

Confidence Score: 5/5

• This PR is safe to merge with minimal risk
• The implementation is clean, type-safe, and well-tested. The change is minimal and focused, adding only 4 lines of code to enable opt-out functionality. Type narrowing ensures no None values are passed to functions expecting non-None configs. The test coverage is comprehensive, validating both the new opt-out behavior and maintaining backward compatibility. No breaking changes or edge cases detected.
• No files require special attention

Important Files Changed

Filename	Overview
reflex/plugins/sitemap.py	Added type-safe opt-out mechanism for sitemap inclusion by checking for explicit None values
tests/units/plugins/test_sitemap.py	Added comprehensive test case validating that pages with sitemap=None are excluded while default pages are included

Sequence Diagram

sequenceDiagram
    participant App as Reflex App
    participant Plugin as SitemapPlugin
    participant Gen as generate_links_for_sitemap
    participant Config as configuration_with_loc
    participant XML as generate_xml
    
    App->>Plugin: pre_compile(unevaluated_pages)
    Plugin->>Gen: sitemap_task(unevaluated_pages)
    
    loop For each page
        Gen->>Gen: page.context.get("sitemap", {})
        
        alt sitemap is None
            Gen->>Gen: skip page (opt-out)
        else sitemap exists
            alt is dynamic/404 route
                alt no config or no loc
                    Gen->>Gen: skip page or warn
                else has loc
                    Gen->>Config: configuration_with_loc(config, deploy_url, loc)
                    Config-->>Gen: SitemapLink
                end
            else static route
                alt has custom loc
                    Gen->>Config: configuration_with_loc(config, deploy_url, loc)
                    Config-->>Gen: SitemapLink
                else use default route
                    Gen->>Config: configuration_with_loc(config, deploy_url, route)
                    Config-->>Gen: SitemapLink
                end
            end
        end
    end
    
    Gen-->>Plugin: list[SitemapLink]
    Plugin->>XML: generate_xml(links)
    XML-->>Plugin: XML string
    Plugin->>App: save to public/sitemap.xml

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