usdt-impl 0.5.0

// Copyright 2022 Oxide Computer Company
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//

use std::env;

#[derive(Copy, Clone)]
enum Backend {
    // Standard (read: illumos) probe registration
    Standard,
    // MacOS linker-aware probe registration
    Linker,
    // Provide probe macros, but probes are no-ops (dtrace-less OSes)
    NoOp,
}

fn main() {
    println!("cargo:rerun-if-changed=build.rs");

    // `asm` feature was stabilized in 1.59
    let have_stable_asm = version_check::is_min_version("1.59").unwrap_or(false);
    // `asm_sym` feature was stabilized in 1.66
    let have_stable_asm_sym = version_check::is_min_version("1.66").unwrap_or(false);

    // Are we being built with a compiler which allows feature flags (nightly)
    let is_nightly = version_check::is_feature_flaggable().unwrap_or(false);

    let feat_asm = env::var_os("CARGO_FEATURE_ASM").is_some();
    let feat_strict_asm = env::var_os("CARGO_FEATURE_STRICT_ASM").is_some();

    let backend = match env::var("CARGO_CFG_TARGET_OS").ok().as_deref() {
        Some("macos") if feat_asm => {
            if have_stable_asm && have_stable_asm_sym {
                Backend::Linker
            } else if feat_strict_asm || is_nightly {
                if !have_stable_asm {
                    println!("cargo:rustc-cfg=usdt_need_feat_asm");
                }
                if !have_stable_asm_sym {
                    println!("cargo:rustc-cfg=usdt_need_feat_asm_sym");
                }
                Backend::Linker
            } else {
                Backend::NoOp
            }
        }
        Some("illumos") | Some("solaris") if feat_asm => {
            if have_stable_asm {
                Backend::Standard
            } else if feat_strict_asm || is_nightly {
                println!("cargo:rustc-cfg=usdt_need_feat_asm");
                Backend::Standard
            } else {
                Backend::NoOp
            }
        }
        _ => {
            if !have_stable_asm {
                println!("cargo:rustc-cfg=usdt_need_feat_asm");
            }
            Backend::NoOp
        }
    };

    // Since visibility of the `asm!()` macro differs between the nightly feature and the
    // stabilized version, the consumer requires information about its availability
    if have_stable_asm {
        println!("cargo:rustc-cfg=usdt_stable_asm");
    }

    match backend {
        Backend::NoOp => {
            println!("cargo:rustc-cfg=usdt_backend_noop");
        }
        Backend::Linker => {
            println!("cargo:rustc-cfg=usdt_backend_linker");
        }
        Backend::Standard => {
            println!("cargo:rustc-cfg=usdt_backend_standard");
        }
    }
}