cmake-0.1.42/src/lib.rs

//! A build dependency for running `cmake` to build a native library
//!
//! This crate provides some necessary boilerplate and shim support for running
//! the system `cmake` command to build a native library. It will add
//! appropriate cflags for building code to link into Rust, handle cross
//! compilation, and use the necessary generator for the platform being
//! targeted.
//!
//! The builder-style configuration allows for various variables and such to be
//! passed down into the build as well.
//!
//! ## Installation
//!
//! Add this to your `Cargo.toml`:
//!
//! ```toml
//! [build-dependencies]
//! cmake = "0.1"
//! ```
//!
//! ## Examples
//!
//! ```no_run
//! use cmake;
//!
//! // Builds the project in the directory located in `libfoo`, installing it
//! // into $OUT_DIR
//! let dst = cmake::build("libfoo");
//!
//! println!("cargo:rustc-link-search=native={}", dst.display());
//! println!("cargo:rustc-link-lib=static=foo");
//! ```
//!
//! ```no_run
//! use cmake::Config;
//!
//! let dst = Config::new("libfoo")
//!                  .define("FOO", "BAR")
//!                  .cflag("-foo")
//!                  .build();
//! println!("cargo:rustc-link-search=native={}", dst.display());
//! println!("cargo:rustc-link-lib=static=foo");
//! ```

#![deny(missing_docs)]

extern crate cc;

use std::env;
use std::ffi::{OsStr, OsString};
use std::fs::{self, File};
use std::io::prelude::*;
use std::io::ErrorKind;
use std::path::{Path, PathBuf};
use std::process::Command;

/// Builder style configuration for a pending CMake build.
pub struct Config {
    path: PathBuf,
    generator: Option<OsString>,
    cflags: OsString,
    cxxflags: OsString,
    defines: Vec<(OsString, OsString)>,
    deps: Vec<String>,
    target: Option<String>,
    host: Option<String>,
    out_dir: Option<PathBuf>,
    profile: Option<String>,
    build_args: Vec<OsString>,
    cmake_target: Option<String>,
    env: Vec<(OsString, OsString)>,
    static_crt: Option<bool>,
    uses_cxx11: bool,
    always_configure: bool,
    no_build_target: bool,
    verbose_cmake: bool,
    verbose_make: bool,
}

/// Builds the native library rooted at `path` with the default cmake options.
/// This will return the directory in which the library was installed.
///
/// # Examples
///
/// ```no_run
/// use cmake;
///
/// // Builds the project in the directory located in `libfoo`, installing it
/// // into $OUT_DIR
/// let dst = cmake::build("libfoo");
///
/// println!("cargo:rustc-link-search=native={}", dst.display());
/// println!("cargo:rustc-link-lib=static=foo");
/// ```
///
pub fn build<P: AsRef<Path>>(path: P) -> PathBuf {
    Config::new(path.as_ref()).build()
}

impl Config {
    /// Creates a new blank set of configuration to build the project specified
    /// at the path `path`.
    pub fn new<P: AsRef<Path>>(path: P) -> Config {
        Config {
            path: env::current_dir().unwrap().join(path),
            generator: None,
            cflags: OsString::new(),
            cxxflags: OsString::new(),
            defines: Vec::new(),
            deps: Vec::new(),
            profile: None,
            out_dir: None,
            target: None,
            host: None,
            build_args: Vec::new(),
            cmake_target: None,
            env: Vec::new(),
            static_crt: None,
            uses_cxx11: false,
            always_configure: true,
            no_build_target: false,
            verbose_cmake: false,
            verbose_make: false,
        }
    }

    /// Sets the build-tool generator (`-G`) for this compilation.
    pub fn generator<T: AsRef<OsStr>>(&mut self, generator: T) -> &mut Config {
        self.generator = Some(generator.as_ref().to_owned());
        self
    }

    /// Adds a custom flag to pass down to the C compiler, supplementing those
    /// that this library already passes.
    pub fn cflag<P: AsRef<OsStr>>(&mut self, flag: P) -> &mut Config {
        self.cflags.push(" ");
        self.cflags.push(flag.as_ref());
        self
    }

    /// Adds a custom flag to pass down to the C++ compiler, supplementing those
    /// that this library already passes.
    pub fn cxxflag<P: AsRef<OsStr>>(&mut self, flag: P) -> &mut Config {
        self.cxxflags.push(" ");
        self.cxxflags.push(flag.as_ref());
        self
    }

    /// Adds a new `-D` flag to pass to cmake during the generation step.
    pub fn define<K, V>(&mut self, k: K, v: V) -> &mut Config
    where
        K: AsRef<OsStr>,
        V: AsRef<OsStr>,
    {
        self.defines
            .push((k.as_ref().to_owned(), v.as_ref().to_owned()));
        self
    }

    /// Registers a dependency for this compilation on the native library built
    /// by Cargo previously.
    ///
    /// This registration will modify the `CMAKE_PREFIX_PATH` environment
    /// variable for the build system generation step.
    pub fn register_dep(&mut self, dep: &str) -> &mut Config {
        self.deps.push(dep.to_string());
        self
    }

    /// Sets the target triple for this compilation.
    ///
    /// This is automatically scraped from `$TARGET` which is set for Cargo
    /// build scripts so it's not necessary to call this from a build script.
    pub fn target(&mut self, target: &str) -> &mut Config {
        self.target = Some(target.to_string());
        self
    }

    /// Disables the cmake target option for this compilation.
    ///
    /// Note that this isn't related to the target triple passed to the compiler!
    pub fn no_build_target(&mut self, no_build_target: bool) -> &mut Config {
        self.no_build_target = no_build_target;
        self
    }

    /// Sets the host triple for this compilation.
    ///
    /// This is automatically scraped from `$HOST` which is set for Cargo
    /// build scripts so it's not necessary to call this from a build script.
    pub fn host(&mut self, host: &str) -> &mut Config {
        self.host = Some(host.to_string());
        self
    }

    /// Sets the output directory for this compilation.
    ///
    /// This is automatically scraped from `$OUT_DIR` which is set for Cargo
    /// build scripts so it's not necessary to call this from a build script.
    pub fn out_dir<P: AsRef<Path>>(&mut self, out: P) -> &mut Config {
        self.out_dir = Some(out.as_ref().to_path_buf());
        self
    }

    /// Sets the `CMAKE_BUILD_TYPE=build_type` variable.
    ///
    /// By default, this value is automatically inferred from Rust's compilation
    /// profile as follows:
    ///
    /// * if `opt-level=0` then `CMAKE_BUILD_TYPE=Debug`,
    /// * if `opt-level={1,2,3}` and:
    ///   * `debug=false` then `CMAKE_BUILD_TYPE=Release`
    ///   * otherwise `CMAKE_BUILD_TYPE=RelWithDebInfo`
    /// * if `opt-level={s,z}` then `CMAKE_BUILD_TYPE=MinSizeRel`
    pub fn profile(&mut self, profile: &str) -> &mut Config {
        self.profile = Some(profile.to_string());
        self
    }

    /// Configures whether the /MT flag or the /MD flag will be passed to msvc build tools.
    ///
    /// This option defaults to `false`, and affect only msvc targets.
    pub fn static_crt(&mut self, static_crt: bool) -> &mut Config {
        self.static_crt = Some(static_crt);
        self
    }

    /// Add an argument to the final `cmake` build step
    pub fn build_arg<A: AsRef<OsStr>>(&mut self, arg: A) -> &mut Config {
        self.build_args.push(arg.as_ref().to_owned());
        self
    }

    /// Configure an environment variable for the `cmake` processes spawned by
    /// this crate in the `build` step.
    pub fn env<K, V>(&mut self, key: K, value: V) -> &mut Config
    where
        K: AsRef<OsStr>,
        V: AsRef<OsStr>,
    {
        self.env
            .push((key.as_ref().to_owned(), value.as_ref().to_owned()));
        self
    }

    /// Sets the build target for the final `cmake` build step, this will
    /// default to "install" if not specified.
    pub fn build_target(&mut self, target: &str) -> &mut Config {
        self.cmake_target = Some(target.to_string());
        self
    }

    /// Alters the default target triple on OSX to ensure that c++11 is
    /// available. Does not change the target triple if it is explicitly
    /// specified.
    ///
    /// This does not otherwise affect any CXX flags, i.e. it does not set
    /// -std=c++11 or -stdlib=libc++.
    pub fn uses_cxx11(&mut self) -> &mut Config {
        self.uses_cxx11 = true;
        self
    }

    /// Forces CMake to always run before building the custom target.
    ///
    /// In some cases, when you have a big project, you can disable
    /// subsequents runs of cmake to make `cargo build` faster.
    pub fn always_configure(&mut self, always_configure: bool) -> &mut Config {
        self.always_configure = always_configure;
        self
    }

    /// Sets very verbose output.
    pub fn very_verbose(&mut self, value: bool) -> &mut Config {
        self.verbose_cmake = value;
        self.verbose_make = value;
        self
    }

    // Simple heuristic to determine if we're cross-compiling using the Android
    // NDK toolchain file.
    fn uses_android_ndk(&self) -> bool {
        // `ANDROID_ABI` is the only required flag:
        // https://developer.android.com/ndk/guides/cmake#android_abi
        self.defined("ANDROID_ABI")
            && self.defines.iter().any(|(flag, value)| {
                flag == "CMAKE_TOOLCHAIN_FILE"
                    && Path::new(value).file_name() == Some("android.toolchain.cmake".as_ref())
            })
    }

    /// Run this configuration, compiling the library with all the configured
    /// options.
    ///
    /// This will run both the build system generator command as well as the
    /// command to build the library.
    pub fn build(&mut self) -> PathBuf {
        let target = match self.target.clone() {
            Some(t) => t,
            None => {
                let mut t = getenv_unwrap("TARGET");
                if t.ends_with("-darwin") && self.uses_cxx11 {
                    t = t + "11"
                }
                t
            }
        };
        let host = self.host.clone().unwrap_or_else(|| getenv_unwrap("HOST"));
        let msvc = target.contains("msvc");
        let ndk = self.uses_android_ndk();
        let mut c_cfg = cc::Build::new();
        c_cfg
            .cargo_metadata(false)
            .opt_level(0)
            .debug(false)
            .warnings(false)
            .host(&host)
            .no_default_flags(ndk);
        if !ndk {
            c_cfg.target(&target);
        }
        let mut cxx_cfg = cc::Build::new();
        cxx_cfg
            .cargo_metadata(false)
            .cpp(true)
            .opt_level(0)
            .debug(false)
            .warnings(false)
            .host(&host)
            .no_default_flags(ndk);
        if !ndk {
            cxx_cfg.target(&target);
        }
        if let Some(static_crt) = self.static_crt {
            c_cfg.static_crt(static_crt);
            cxx_cfg.static_crt(static_crt);
        }
        let c_compiler = c_cfg.get_compiler();
        let cxx_compiler = cxx_cfg.get_compiler();

        let dst = self
            .out_dir
            .clone()
            .unwrap_or_else(|| PathBuf::from(getenv_unwrap("OUT_DIR")));
        let build = dst.join("build");
        self.maybe_clear(&build);
        let _ = fs::create_dir(&build);

        // Add all our dependencies to our cmake paths
        let mut cmake_prefix_path = Vec::new();
        for dep in &self.deps {
            let dep = dep.to_uppercase().replace('-', "_");
            if let Some(root) = env::var_os(&format!("DEP_{}_ROOT", dep)) {
                cmake_prefix_path.push(PathBuf::from(root));
            }
        }
        let system_prefix = env::var_os("CMAKE_PREFIX_PATH").unwrap_or(OsString::new());
        cmake_prefix_path.extend(env::split_paths(&system_prefix).map(|s| s.to_owned()));
        let cmake_prefix_path = env::join_paths(&cmake_prefix_path).unwrap();

        // Build up the first cmake command to build the build system.
        let executable = env::var("CMAKE").unwrap_or("cmake".to_owned());
        let mut cmd = Command::new(&executable);

        if self.verbose_cmake {
            cmd.arg("-Wdev");
            cmd.arg("--debug-output");
        }

        cmd.arg(&self.path).current_dir(&build);
        let mut is_ninja = false;
        if let Some(ref generator) = self.generator {
            is_ninja = generator.to_string_lossy().contains("Ninja");
        }
        if target.contains("windows-gnu") {
            if host.contains("windows") {
                // On MinGW we need to coerce cmake to not generate a visual
                // studio build system but instead use makefiles that MinGW can
                // use to build.
                if self.generator.is_none() {
                    // If make.exe isn't found, that means we may be using a MinGW
                    // toolchain instead of a MSYS2 toolchain. If neither is found,
                    // the build cannot continue.
                    let has_msys2 = Command::new("make")
                        .arg("--version")
                        .output()
                        .err()
                        .map(|e| e.kind() != ErrorKind::NotFound)
                        .unwrap_or(true);
                    let has_mingw32 = Command::new("mingw32-make")
                        .arg("--version")
                        .output()
                        .err()
                        .map(|e| e.kind() != ErrorKind::NotFound)
                        .unwrap_or(true);

                    let generator = match (has_msys2, has_mingw32) {
                        (true, _) => "MSYS Makefiles",
                        (false, true) => "MinGW Makefiles",
                        (false, false) => fail("no valid generator found for GNU toolchain; MSYS or MinGW must be installed")
                    };

                    cmd.arg("-G").arg(generator);
                }
            } else {
                // If we're cross compiling onto windows, then set some
                // variables which will hopefully get things to succeed. Some
                // systems may need the `windres` or `dlltool` variables set, so
                // set them if possible.
                if !self.defined("CMAKE_SYSTEM_NAME") {
                    cmd.arg("-DCMAKE_SYSTEM_NAME=Windows");
                }
                if !self.defined("CMAKE_RC_COMPILER") {
                    let exe = find_exe(c_compiler.path());
                    if let Some(name) = exe.file_name().unwrap().to_str() {
                        let name = name.replace("gcc", "windres");
                        let windres = exe.with_file_name(name);
                        if windres.is_file() {
                            let mut arg = OsString::from("-DCMAKE_RC_COMPILER=");
                            arg.push(&windres);
                            cmd.arg(arg);
                        }
                    }
                }
            }
        } else if msvc {
            // If we're on MSVC we need to be sure to use the right generator or
            // otherwise we won't get 32/64 bit correct automatically.
            // This also guarantees that NMake generator isn't chosen implicitly.
            let using_nmake_generator;
            if self.generator.is_none() {
                cmd.arg("-G").arg(self.visual_studio_generator(&target));
                using_nmake_generator = false;
            } else {
                using_nmake_generator = self.generator.as_ref().unwrap() == "NMake Makefiles";
            }
            if !is_ninja && !using_nmake_generator {
                if target.contains("x86_64") {
                    cmd.arg("-Thost=x64");
                    cmd.arg("-Ax64");
                } else if target.contains("thumbv7a") {
                    cmd.arg("-Thost=x64");
                    cmd.arg("-Aarm");
                } else if target.contains("aarch64") {
                    cmd.arg("-Thost=x64");
                    cmd.arg("-AARM64");
                } else if target.contains("i686") {
                    use cc::windows_registry::{find_vs_version, VsVers};
                    match find_vs_version() {
                        Ok(VsVers::Vs16) => {
                            // 32-bit x86 toolset used to be the default for all hosts,
                            // but Visual Studio 2019 changed the default toolset to match the host,
                            // so we need to manually override it for x86 targets
                            cmd.arg("-Thost=x86");
                            cmd.arg("-AWin32");
                        }
                        _ => {}
                    };
                } else {
                    panic!("unsupported msvc target: {}", target);
                }
            }
        } else if target.contains("redox") {
            if !self.defined("CMAKE_SYSTEM_NAME") {
                cmd.arg("-DCMAKE_SYSTEM_NAME=Generic");
            }
        } else if target.contains("solaris") {
            if !self.defined("CMAKE_SYSTEM_NAME") {
                cmd.arg("-DCMAKE_SYSTEM_NAME=SunOS");
            }
        }
        if let Some(ref generator) = self.generator {
            cmd.arg("-G").arg(generator);
        }
        let profile = self.profile.clone().unwrap_or_else(|| {
            // Automatically set the `CMAKE_BUILD_TYPE` if the user did not
            // specify one.

            // Determine Rust's profile, optimization level, and debug info:
            #[derive(PartialEq)]
            enum RustProfile {
                Debug,
                Release,
            }
            #[derive(PartialEq, Debug)]
            enum OptLevel {
                Debug,
                Release,
                Size,
            }

            let rust_profile = match &getenv_unwrap("PROFILE")[..] {
                "debug" => RustProfile::Debug,
                "release" | "bench" => RustProfile::Release,
                unknown => {
                    eprintln!(
                        "Warning: unknown Rust profile={}; defaulting to a release build.",
                        unknown
                    );
                    RustProfile::Release
                }
            };

            let opt_level = match &getenv_unwrap("OPT_LEVEL")[..] {
                "0" => OptLevel::Debug,
                "1" | "2" | "3" => OptLevel::Release,
                "s" | "z" => OptLevel::Size,
                unknown => {
                    let default_opt_level = match rust_profile {
                        RustProfile::Debug => OptLevel::Debug,
                        RustProfile::Release => OptLevel::Release,
                    };
                    eprintln!(
                        "Warning: unknown opt-level={}; defaulting to a {:?} build.",
                        unknown, default_opt_level
                    );
                    default_opt_level
                }
            };

            let debug_info: bool = match &getenv_unwrap("DEBUG")[..] {
                "false" => false,
                "true" => true,
                unknown => {
                    eprintln!("Warning: unknown debug={}; defaulting to `true`.", unknown);
                    true
                }
            };

            match (opt_level, debug_info) {
                (OptLevel::Debug, _) => "Debug",
                (OptLevel::Release, false) => "Release",
                (OptLevel::Release, true) => "RelWithDebInfo",
                (OptLevel::Size, _) => "MinSizeRel",
            }
            .to_string()
        });
        for &(ref k, ref v) in &self.defines {
            let mut os = OsString::from("-D");
            os.push(k);
            os.push("=");
            os.push(v);
            cmd.arg(os);
        }

        if !self.defined("CMAKE_INSTALL_PREFIX") {
            let mut dstflag = OsString::from("-DCMAKE_INSTALL_PREFIX=");
            dstflag.push(&dst);
            cmd.arg(dstflag);
        }

        let build_type = self
            .defines
            .iter()
            .find(|&&(ref a, _)| a == "CMAKE_BUILD_TYPE")
            .map(|x| x.1.to_str().unwrap())
            .unwrap_or(&profile);
        let build_type_upcase = build_type
            .chars()
            .flat_map(|c| c.to_uppercase())
            .collect::<String>();

        {
            // let cmake deal with optimization/debuginfo
            let skip_arg = |arg: &OsStr| match arg.to_str() {
                Some(s) => s.starts_with("-O") || s.starts_with("/O") || s == "-g",
                None => false,
            };
            let mut set_compiler = |kind: &str, compiler: &cc::Tool, extra: &OsString| {
                let flag_var = format!("CMAKE_{}_FLAGS", kind);
                let tool_var = format!("CMAKE_{}_COMPILER", kind);
                if !self.defined(&flag_var) {
                    let mut flagsflag = OsString::from("-D");
                    flagsflag.push(&flag_var);
                    flagsflag.push("=");
                    flagsflag.push(extra);
                    for arg in compiler.args() {
                        if skip_arg(arg) {
                            continue;
                        }
                        flagsflag.push(" ");
                        flagsflag.push(arg);
                    }
                    cmd.arg(flagsflag);
                }

                // The visual studio generator apparently doesn't respect
                // `CMAKE_C_FLAGS` but does respect `CMAKE_C_FLAGS_RELEASE` and
                // such. We need to communicate /MD vs /MT, so set those vars
                // here.
                //
                // Note that for other generators, though, this *overrides*
                // things like the optimization flags, which is bad.
                if self.generator.is_none() && msvc {
                    let flag_var_alt = format!("CMAKE_{}_FLAGS_{}", kind, build_type_upcase);
                    if !self.defined(&flag_var_alt) {
                        let mut flagsflag = OsString::from("-D");
                        flagsflag.push(&flag_var_alt);
                        flagsflag.push("=");
                        flagsflag.push(extra);
                        for arg in compiler.args() {
                            if skip_arg(arg) {
                                continue;
                            }
                            flagsflag.push(" ");
                            flagsflag.push(arg);
                        }
                        cmd.arg(flagsflag);
                    }
                }

                // Apparently cmake likes to have an absolute path to the
                // compiler as otherwise it sometimes thinks that this variable
                // changed as it thinks the found compiler, /usr/bin/cc,
                // differs from the specified compiler, cc. Not entirely sure
                // what's up, but at least this means cmake doesn't get
                // confused?
                //
                // Also specify this on Windows only if we use MSVC with Ninja,
                // as it's not needed for MSVC with Visual Studio generators and
                // for MinGW it doesn't really vary.
                if !self.defined("CMAKE_TOOLCHAIN_FILE")
                    && !self.defined(&tool_var)
                    && (env::consts::FAMILY != "windows" || (msvc && is_ninja))
                {
                    let mut ccompiler = OsString::from("-D");
                    ccompiler.push(&tool_var);
                    ccompiler.push("=");
                    ccompiler.push(find_exe(compiler.path()));
                    #[cfg(windows)]
                    {
                        // CMake doesn't like unescaped `\`s in compiler paths
                        // so we either have to escape them or replace with `/`s.
                        use std::os::windows::ffi::{OsStrExt, OsStringExt};
                        let wchars = ccompiler
                            .encode_wide()
                            .map(|wchar| {
                                if wchar == b'\\' as u16 {
                                    '/' as u16
                                } else {
                                    wchar
                                }
                            })
                            .collect::<Vec<_>>();
                        ccompiler = OsString::from_wide(&wchars);
                    }
                    cmd.arg(ccompiler);
                }
            };

            set_compiler("C", &c_compiler, &self.cflags);
            set_compiler("CXX", &cxx_compiler, &self.cxxflags);
        }

        if !self.defined("CMAKE_BUILD_TYPE") {
            cmd.arg(&format!("-DCMAKE_BUILD_TYPE={}", profile));
        }

        if self.verbose_make {
            cmd.arg("-DCMAKE_VERBOSE_MAKEFILE:BOOL=ON");
        }

        if !self.defined("CMAKE_TOOLCHAIN_FILE") {
            if let Ok(s) = env::var("CMAKE_TOOLCHAIN_FILE") {
                cmd.arg(&format!("-DCMAKE_TOOLCHAIN_FILE={}", s));
            }
        }

        for &(ref k, ref v) in c_compiler.env().iter().chain(&self.env) {
            cmd.env(k, v);
        }

        if self.always_configure || !build.join("CMakeCache.txt").exists() {
            run(cmd.env("CMAKE_PREFIX_PATH", cmake_prefix_path), "cmake");
        } else {
            println!("CMake project was already configured. Skipping configuration step.");
        }

        let mut makeflags = None;
        let mut parallel_flags = None;

        if let Ok(s) = env::var("NUM_JOBS") {
            match self.generator.as_ref().map(|g| g.to_string_lossy()) {
                Some(ref g) if g.contains("Ninja") => {
                    parallel_flags = Some(format!("-j{}", s));
                }
                Some(ref g) if g.contains("Visual Studio") => {
                    parallel_flags = Some(format!("/m:{}", s));
                }
                Some(ref g) if g.contains("NMake") => {
                    // NMake creates `Makefile`s, but doesn't understand `-jN`.
                }
                _ if fs::metadata(&build.join("Makefile")).is_ok() => {
                    match env::var_os("CARGO_MAKEFLAGS") {
                        // Only do this on non-windows and non-bsd
                        // On Windows, we could be invoking make instead of
                        // mingw32-make which doesn't work with our jobserver
                        // bsdmake also does not work with our job server
                        Some(ref s)
                            if !(cfg!(windows)
                                || cfg!(target_os = "openbsd")
                                || cfg!(target_os = "netbsd")
                                || cfg!(target_os = "freebsd")
                                || cfg!(target_os = "bitrig")
                                || cfg!(target_os = "dragonflybsd")) =>
                        {
                            makeflags = Some(s.clone())
                        }

                        // This looks like `make`, let's hope it understands `-jN`.
                        _ => makeflags = Some(OsString::from(format!("-j{}", s))),
                    }
                }
                _ => {}
            }
        }

        // And build!
        let target = self.cmake_target.clone().unwrap_or("install".to_string());
        let mut cmd = Command::new(&executable);
        for &(ref k, ref v) in c_compiler.env().iter().chain(&self.env) {
            cmd.env(k, v);
        }

        if let Some(flags) = makeflags {
            cmd.env("MAKEFLAGS", flags);
        }

        cmd.arg("--build").arg(".");

        if !self.no_build_target {
            cmd.arg("--target").arg(target);
        }

        cmd.arg("--config")
            .arg(&profile)
            .arg("--")
            .args(&self.build_args)
            .current_dir(&build);

        if let Some(flags) = parallel_flags {
            cmd.arg(flags);
        }

        run(&mut cmd, "cmake");

        println!("cargo:root={}", dst.display());
        return dst;
    }

    fn visual_studio_generator(&self, target: &str) -> String {
        use cc::windows_registry::{find_vs_version, VsVers};

        let base = match find_vs_version() {
            Ok(VsVers::Vs16) => "Visual Studio 16 2019",
            Ok(VsVers::Vs15) => "Visual Studio 15 2017",
            Ok(VsVers::Vs14) => "Visual Studio 14 2015",
            Ok(VsVers::Vs12) => "Visual Studio 12 2013",
            Ok(_) => panic!(
                "Visual studio version detected but this crate \
                 doesn't know how to generate cmake files for it, \
                 can the `cmake` crate be updated?"
            ),
            Err(msg) => panic!(msg),
        };
        if ["i686", "x86_64", "thumbv7a", "aarch64"]
            .iter()
            .any(|t| target.contains(t))
        {
            base.to_string()
        } else {
            panic!("unsupported msvc target: {}", target);
        }
    }

    fn defined(&self, var: &str) -> bool {
        self.defines.iter().any(|&(ref a, _)| a == var)
    }

    // If a cmake project has previously been built (e.g. CMakeCache.txt already
    // exists), then cmake will choke if the source directory for the original
    // project being built has changed. Detect this situation through the
    // `CMAKE_HOME_DIRECTORY` variable that cmake emits and if it doesn't match
    // we blow away the build directory and start from scratch (the recommended
    // solution apparently [1]).
    //
    // [1]: https://cmake.org/pipermail/cmake/2012-August/051545.html
    fn maybe_clear(&self, dir: &Path) {
        // CMake will apparently store canonicalized paths which normally
        // isn't relevant to us but we canonicalize it here to ensure
        // we're both checking the same thing.
        let path = fs::canonicalize(&self.path).unwrap_or(self.path.clone());
        let mut f = match File::open(dir.join("CMakeCache.txt")) {
            Ok(f) => f,
            Err(..) => return,
        };
        let mut u8contents = Vec::new();
        match f.read_to_end(&mut u8contents) {
            Ok(f) => f,
            Err(..) => return,
        };
        let contents = String::from_utf8_lossy(&u8contents);
        drop(f);
        for line in contents.lines() {
            if line.starts_with("CMAKE_HOME_DIRECTORY") {
                let needs_cleanup = match line.split('=').next_back() {
                    Some(cmake_home) => fs::canonicalize(cmake_home)
                        .ok()
                        .map(|cmake_home| cmake_home != path)
                        .unwrap_or(true),
                    None => true,
                };
                if needs_cleanup {
                    println!(
                        "detected home dir change, cleaning out entire build \
                         directory"
                    );
                    fs::remove_dir_all(dir).unwrap();
                }
                break;
            }
        }
    }
}

fn run(cmd: &mut Command, program: &str) {
    println!("running: {:?}", cmd);
    let status = match cmd.status() {
        Ok(status) => status,
        Err(ref e) if e.kind() == ErrorKind::NotFound => {
            fail(&format!(
                "failed to execute command: {}\nis `{}` not installed?",
                e, program
            ));
        }
        Err(e) => fail(&format!("failed to execute command: {}", e)),
    };
    if !status.success() {
        fail(&format!(
            "command did not execute successfully, got: {}",
            status
        ));
    }
}

fn find_exe(path: &Path) -> PathBuf {
    env::split_paths(&env::var_os("PATH").unwrap_or(OsString::new()))
        .map(|p| p.join(path))
        .find(|p| fs::metadata(p).is_ok())
        .unwrap_or(path.to_owned())
}

fn getenv_unwrap(v: &str) -> String {
    match env::var(v) {
        Ok(s) => s,
        Err(..) => fail(&format!("environment variable `{}` not defined", v)),
    }
}

fn fail(s: &str) -> ! {
    panic!("\n{}\n\nbuild script failed, must exit now", s)
}