feat(sys)!: make HTTP and Stream bindings generation optional

[bavshin-f5]

Generate bindings for ngx_http.h and ngx_stream.h only when requested via corresponding feature flags and supported in the build of NGINX. (HTTP is still enabled in the default feature set.)

This allows following previously impossible scenarios:

• building Core modules without HTTP dependency.
• building Stream modules for NGINX configured with --without-http.

Also add Mail support and more ngx_feature flags.

[Copilot]

Pull request overview

This PR makes generation and exposure of NGINX subsystem bindings (HTTP/Stream/Mail) conditional on both Cargo feature flags and the capabilities enabled in the target NGINX build, enabling builds that omit HTTP while still supporting Stream or Core-only modules.

Changes:

• Gate nginx-sys HTTP/Stream modules behind feature && ngx_feature and add optional Mail bindings behind mail.
• Update bindgen wrapper/build logic to include ngx_http.h/ngx_stream.h/ngx_mail.h only when the corresponding Cargo feature is enabled (and headers are available).
• Expand detected/exported NGINX feature flags and enable Mail in vendored nginx-src default configure arguments.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/lib.rs	Gate high-level ngx::http module on ngx_feature="http".
nginx-sys/src/mail.rs	Add Mail conf ctx field offset constants.
nginx-sys/src/lib.rs	Conditionally compile/re-export http/mail/stream modules using Cargo features + ngx_feature.
nginx-sys/README.md	Document new http (default), mail, stream feature flags and behavior.
nginx-sys/Cargo.toml	Define http default feature plus mail/stream features.
nginx-sys/build/wrapper.h	Feature-gate inclusion of module headers during bindgen.
nginx-sys/build/main.rs	Add more exported ngx_feature flags and define NGX_RS_FEATURE_* bindgen macros based on Cargo features.
nginx-src/src/lib.rs	Enable Mail modules in the default vendored configure args.
examples/Cargo.toml	Switch examples back to default nginx-sys features (HTTP enabled).

Comments suppressed due to low confidence (1)

nginx-sys/build/main.rs:447

• In expand_definitions(), the #else /* fallback */ branch assumes RUST_CONF_HTTP=1 but does not set RUST_CONF_MAIL or RUST_CONF_STREAM. This becomes inconsistent now that Mail/Stream support is feature-detected via __has_include: on toolchains lacking __has_include, Mail/Stream will never be reported in DEP_NGINX_FEATURES, and HTTP may be reported even when headers aren’t available. Consider either (1) implementing a more accurate fallback for all three headers, or (2) removing the fallback and requiring __has_include (since the wrapper comment already assumes bindgen/libclang support).

/* C23 or Clang/GCC/MSVC >= 15.3 extension */
#if defined(__has_include)

#if __has_include(<ngx_http.h>)
RUST_CONF_HTTP=1
#endif

#if __has_include(<ngx_mail.h>)
RUST_CONF_MAIL=1
#endif

#if __has_include(<ngx_stream.h>)
RUST_CONF_STREAM=1
#endif

#else
/* fallback */
RUST_CONF_HTTP=1
#endif

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