Don't link binaries on docs.rs

Author: kornelski

boring-sys/build/config.rs

@@ -36,6 +36,7 @@ pub(crate) struct Env {
     pub(crate) android_ndk_home: Option<PathBuf>,
     pub(crate) cmake_toolchain_file: Option<PathBuf>,
     pub(crate) cpp_runtime_lib: Option<OsString>,
+    pub(crate) docs_rs: bool,
 }
 
 impl Config {
@@ -185,6 +186,7 @@ impl Env {
             android_ndk_home: target_var("ANDROID_NDK_HOME").map(Into::into),
             cmake_toolchain_file: target_var("CMAKE_TOOLCHAIN_FILE").map(Into::into),
             cpp_runtime_lib: target_var("BORING_BSSL_RUST_CPPLIB"),
+            docs_rs: var("DOCS_RS").is_some(),
         }
     }
 }

boring-sys/build/main.rs

@@ -656,6 +656,13 @@ fn get_cpp_runtime_lib(config: &Config) -> Option<String> {
 
 fn main() {
     let config = Config::from_env();
+    if !config.env.docs_rs {
+        emit_link_directives(&config);
+    }
+    generate_bindings(&config);
+}
+
+fn emit_link_directives(config: &Config) {
     let bssl_dir = built_boring_source_path(&config);
     let build_path = get_boringssl_platform_output_path(&config);
 
@@ -702,7 +709,9 @@ fn main() {
         // Rust 1.87.0 compat - https://github.com/rust-lang/rust/pull/138233
         println!("cargo:rustc-link-lib=advapi32");
     }
+}
 
+fn generate_bindings(config: &Config) {
     let include_path = config.env.include_path.clone().unwrap_or_else(|| {
         if let Some(bssl_path) = &config.env.path {
             return bssl_path.join("include");