Implement 'download-z3' flag

In some system, `cargo test --doc` may fail due to the bug:
rust-lang/cargo#8531

z3-sys/Cargo.toml

@@ -18,8 +18,12 @@ repository = "https://github.com/prove-rs/z3.rs.git"
 [build-dependencies]
 bindgen = { version = "0.66.0", default-features = false, features = ["runtime"] }
 cmake = { version = "0.1.49", optional = true }
+sha2 = { version = "~0.7.0", optional = true }
+zip = { version = "~0.3.1", optional = true }
+reqwest = { version = "0.11", features = ["blocking"], optional = true }
 
 [features]
 # Enable this feature to statically link our own build of Z3, rather than
 # dynamically linking to the system's `libz3.so`.
 static-link-z3 = ["cmake"]
+download-z3 = ["sha2", "zip", "reqwest"]

z3-sys/build.rs

@@ -6,6 +6,9 @@ fn main() {
     #[cfg(feature = "static-link-z3")]
     build_z3();
 
+    #[cfg(all(not(feature = "static-link-z3"), feature = "download-z3"))]
+    let include_dir = download_z3();
+
     println!("cargo:rerun-if-changed=build.rs");
 
     let header = if cfg!(feature = "static-link-z3") {
@@ -36,6 +39,12 @@ fn main() {
             .generate_comments(false)
             .rustified_enum(format!("Z3_{}", x))
             .allowlist_type(format!("Z3_{}", x));
+
+        #[cfg(all(not(feature = "static-link-z3"), feature = "download-z3"))]
+        {
+            enum_bindings = enum_bindings.clang_arg(&format!("-I{}", &include_dir));
+        }
+
         if env::var("TARGET").unwrap() == "wasm32-unknown-emscripten" {
             enum_bindings = enum_bindings.clang_arg(format!(
                 "--sysroot={}/upstream/emscripten/cache/sysroot",
@@ -128,3 +137,113 @@ fn build_z3() {
         println!("cargo:rustc-link-lib={}", cxx);
     }
 }
+
+#[cfg(feature = "download-z3")]
+fn download_z3() -> String {
+    use reqwest::blocking;
+    use sha2::{Digest, Sha256};
+    use std::fs::File;
+    use std::io::{Cursor, Read, Write};
+    use std::path::{Path, PathBuf};
+    use zip::ZipArchive;
+    fn download(url: &str, sha256: &str) -> Result<Vec<u8>, String> {
+        let buf = (|| -> reqwest::Result<_> {
+            let response = blocking::get(url)?.error_for_status()?;
+            Ok(response.bytes()?.iter().cloned().collect::<Vec<_>>())
+        })()
+        .map_err(|e| e.to_string())?;
+        if sha256 != "PASS" {
+            let hash = Sha256::digest(&buf);
+            if &format!("{:x}", hash) != sha256 {
+                return Err("Hash check failed".to_string());
+            }
+        }
+        Ok(buf)
+    }
+
+    fn get_archive_url() -> Option<(String, String)> {
+        if cfg!(target_os = "linux") && cfg!(target_arch = "x86_64") {
+            Some((
+                "https://github.com/Z3Prover/z3/releases/download/z3-4.12.1/z3_solver-4.12.1.0-py2.py3-none-manylinux1_x86_64.whl".into(),
+                "41cb9ac460af30b193811eebf919d61cf51a8856bbd74b200cbe6b21e3e955e4".into(),
+            ))
+        } else if cfg!(target_os = "macos") && cfg!(target_arch = "x86_64") {
+            Some((
+                "https://github.com/Z3Prover/z3/releases/download/z3-4.12.1/z3_solver-4.12.1.0-py2.py3-none-macosx_10_16_x86_64.whl".into(),
+                "c4f1a53bce12b45698e8e49bd980cd3d3f0298c1ba4cf8c40525af86797565c8".into(),
+            ))
+        } else if cfg!(target_os = "macos") && cfg!(target_arch = "aarch64") {
+            Some((
+                "https://github.com/Z3Prover/z3/releases/download/z3-4.12.1/z3_solver-4.12.1.0-py2.py3-none-macosx_11_0_arm64.whl".into(),
+                "553ec3cd0188420bc5f007dd873fb0d87075d1b93808eca8c02324eb3a5f6f68".into(),
+            ))
+        } else if cfg!(target_os = "windows") && cfg!(target_arch = "x86_64") {
+            Some((
+                "https://github.com/Z3Prover/z3/releases/download/z3-4.12.1/z3_solver-4.12.1.0-py2.py3-none-win_amd64.whl".into(),
+                "aa0e06d42070774a2f89818c412514d41fc84578f32d617de618b214e5ed8154".into(),
+            ))
+        } else if cfg!(target_os = "windows") && cfg!(target_arch = "x86") {
+            Some((
+                "https://github.com/Z3Prover/z3/releases/download/z3-4.12.1/z3_solver-4.12.1.0-py2.py3-none-win32.whl".into(),
+                "85ff9f59b0f87df4dc0cd52baebb247b8049f2df6aad623151f4c4a21d3d01ac".into(),
+            ))
+        } else {
+            None
+        }
+    }
+
+    fn write_lib_to_dir(out_dir: &Path) {
+        if let Some((url, hash)) = get_archive_url() {
+            let archive = download(&url, &hash).unwrap();
+            let mut archive = ZipArchive::new(Cursor::new(archive)).unwrap();
+            for i in 0..archive.len() {
+                let mut file = archive.by_index(i).unwrap();
+                let name = file.name().to_string();
+                match name.rsplit_once('/') {
+                    Some((rpath, basename)) => match rpath.rsplit_once('/') {
+                        Some((rrpath, kind))
+                            if rrpath == "z3" && (kind == "lib" || kind == "include") =>
+                        {
+                            let mut buf = Vec::with_capacity(file.size() as usize);
+                            file.read_to_end(&mut buf).unwrap();
+                            let mut outpath = out_dir.to_path_buf();
+                            outpath.push(kind);
+                            std::fs::create_dir_all(&outpath).unwrap();
+                            outpath.push(basename);
+                            let mut outfile = File::create(&outpath).unwrap();
+                            outfile.write_all(&buf).unwrap();
+                        }
+                        _ => {}
+                    },
+                    _ => {}
+                }
+            }
+            println!("cargo:Z3_DOWNLOADED=true");
+        }
+    }
+
+    let out_dir = PathBuf::from(env::var("OUT_DIR").unwrap());
+    let mut out_dir_lib = out_dir.clone();
+    out_dir_lib.push("lib");
+    let mut out_dir_include = out_dir.clone();
+    out_dir_include.push("include");
+    if std::fs::read_dir(&out_dir_lib).is_err() || std::fs::read_dir(&out_dir_include).is_err() {
+        write_lib_to_dir(&out_dir);
+    }
+    println!(
+        "cargo:rustc-link-search=native={}",
+        out_dir_lib.to_str().unwrap()
+    );
+
+    if cfg!(target_os = "windows") {
+        println!("cargo:rustc-link-lib=dylib=libz3");
+    } else {
+        println!("cargo:rustc-link-lib=dylib=z3");
+    }
+
+    std::fs::canonicalize(out_dir_include)
+        .unwrap()
+        .to_str()
+        .unwrap()
+        .to_string()
+}

z3/Cargo.toml

@@ -20,6 +20,7 @@ arbitrary-size-numeral = ["num"]
 # Enable this feature to statically link our own build of Z3, rather than
 # dynamically linking to the system's `libz3.so`.
 static-link-z3 = ["z3-sys/static-link-z3"]
+download-z3 = ["z3-sys/download-z3"]
 
 [dependencies]
 log = "0.4"