src/cfg.rs

// Copyright 2020 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use anyhow::{anyhow, Result};

/// Converts a cargo platform-specific dependency target into GN imperative control flow.
///
/// `Cargo.toml` files can define [platform-specific dependencies] in two ways:
/// - Using `#[cfg]` syntax to match classes of targets.
///   ```text
///   [target.'cfg(unix)'.dependencies]
///   foo = "0.1"
///   ```
///
/// - Listing the full target the dependencies would apply to.
///   ```text
///   [target.aarch64-apple-darwin.dependencies]
///   bar = "0.1"
///   ```
///
/// This function is a wrapper around [`cfg_to_gn_conditional`] that converts full targets
/// into `#[cfg]` syntax.
///
/// [platform-specific dependencies]: https://doc.rust-lang.org/cargo/reference/specifying-dependencies.html#platform-specific-dependencies
pub fn target_to_gn_conditional(target: &str) -> Result<String> {
    if target.starts_with("cfg") {
        // This is #[cfg] syntax already.
        cfg_to_gn_conditional(target)
    } else if target.contains('-') {
        // Handle this as a target triple. We only need to support targets in crates we
        // depend on, so we use a simple exact match list that can be updated as needed.
        let (target_arch, target_os) = match target {
            "aarch64-apple-darwin" => ("aarch64", "macos"),
            "riscv32i-unknown-none-elf" => ("riscv32i", "unknown"),
            "riscv32imc-unknown-none-elf" => ("riscv32imc", "unknown"),
            "thumbv6m-none-eabi" => ("thumbv6m", "unknown"),
            // Return an error for unknown targets, to notify the dev that they should
            // update this list.
            _ => {
                return Err(anyhow!(
                    "Unknown target: {}. Please add this to 'tools/cargo-gnaw/src/cfg.rs'.",
                    target
                ))
            }
        };
        cfg_to_gn_conditional(&format!(
            "cfg(all(target_arch = \"{}\", target_os = \"{}\"))",
            target_arch, target_os
        ))
    } else {
        Err(anyhow!("Unknown platform-specific dependency target syntax: {}", target))
    }
}

/// Convert a cargo cfg conditional into GN imperative control flow
// TODO This should consume some information in the Cargo.toml file
// to establish conventions for the carge -> GN build. This is hardcoded
// to support Fuchsia at the moment.
//
// wow. an interview question in real life.
pub fn cfg_to_gn_conditional(cfg: &str) -> Result<String> {
    #[allow(clippy::if_same_then_else)]
    if cfg.starts_with("cfg") {
        Ok(cfg_to_gn_conditional(&cfg[4..cfg.len() - 1])?)
    } else if cfg.starts_with("not") {
        let section = &cfg[4..];
        let mut paren_count = 1;
        for (idx, c) in section.chars().enumerate() {
            if c == ')' {
                paren_count -= 1;
                if paren_count == 0 {
                    return Ok(format!("!({})", cfg_to_gn_conditional(&section[..idx])?));
                }
            } else if c == '(' {
                paren_count += 1;
            }
        }
        Err(anyhow!("bad not statement"))
    } else if cfg == "any()" {
        Ok(String::from("true"))
    } else if cfg.starts_with("any") {
        let section = &cfg[4..cfg.len()];
        let mut accum = vec![];
        let mut paren_count = 1;
        let mut start_idx = 0;
        for (idx, c) in section.chars().enumerate() {
            if c == ')' {
                paren_count -= 1;
                if paren_count == 0 {
                    accum.push(cfg_to_gn_conditional(&section[start_idx..idx])?);
                }
            } else if c == '(' {
                paren_count += 1;
            } else if c == ',' && paren_count <= 1 {
                accum.push(cfg_to_gn_conditional(&section[start_idx..idx])?);
                start_idx = idx + 2; // skip ", "
            }
        }
        Ok(format!("({})", accum.join(" || ")))
    } else if cfg.starts_with("all") {
        let section = &cfg[4..cfg.len()];
        let mut accum = vec![];
        let mut paren_count = 1;
        let mut start_idx = 0;
        for (idx, c) in section.chars().enumerate() {
            if c == ')' {
                paren_count -= 1;
                if paren_count == 0 {
                    accum.push(cfg_to_gn_conditional(&section[start_idx..idx])?);
                }
            } else if c == '(' {
                paren_count += 1;
            } else if c == ',' && paren_count <= 1 {
                accum.push(cfg_to_gn_conditional(&section[start_idx..idx])?);
                start_idx = idx + 2; // skip ", "
            }
        }
        Ok(format!("({})", accum.join(" && ")))
    } else if cfg == "target_os = \"fuchsia\"" {
        Ok(String::from("current_os == \"fuchsia\""))
    } else if cfg == "target_os = \"macos\"" {
        Ok(String::from("current_os == \"mac\""))
    } else if cfg == "target_os = \"linux\"" {
        Ok(String::from("current_os == \"linux\""))
    } else if cfg == "target_os = \"unknown\"" {
        Ok(String::from("current_os == \"unknown\""))
    } else if cfg == "unix" {
        // all our platforms are unix
        Ok(String::from("true"))
    } else if cfg == "feature = \"std\"" {
        // need to detect std usage
        Ok(String::from("true"))
    } else if cfg == "target_arch = \"aarch64\"" {
        Ok(String::from("current_cpu == \"arm64\""))
    } else if cfg == "target_arch = \"x86_64\"" {
        Ok(String::from("current_cpu == \"x64\""))
    } else if cfg == "target_arch = \"wasm32\"" {
        Ok(String::from("current_cpu == \"wasm32\""))
    } else if cfg == "target_arch = \"riscv32i\"" {
        Ok(String::from("current_cpu == \"riscv32\""))
    } else if cfg == "target_arch = \"riscv32imc\"" {
        Ok(String::from("current_cpu == \"riscv32\""))
    } else if cfg == "target_arch = \"thumbv6m\"" {
        Ok(String::from("current_cpu == \"arm\""))
    } else if cfg == "windows" || cfg == "target_family = \"windows\"" {
        // don't support host builds on windows right now
        Ok(String::from("false"))

    // Everything below is random cfgs that we don't know anything about
    } else if cfg.starts_with("target_os") {
        Ok(String::from("false"))
    } else if cfg.starts_with("target_arch") {
        Ok(String::from("false"))
    } else if cfg.starts_with("target_env") {
        Ok(String::from("false"))
    } else if cfg.starts_with("target_feature") {
        Ok(String::from("false"))
    } else if cfg.starts_with("target_vendor") {
        Ok(String::from("false"))
    } else if cfg.starts_with("tokio_taskdump") {
        Ok(String::from("false"))
    } else if cfg.starts_with("tokio_unstable") {
        Ok(String::from("false"))
    } else if cfg.starts_with("tracing_unstable") {
        Ok(String::from("false"))
    } else if cfg.starts_with("docsrs") {
        Ok(String::from("false"))
    } else {
        // TODO(https://fxbug.dev/42061225) better handling needed for these cases.
        Err(anyhow!("Unknown cfg option used: {}", cfg))
    }
}

#[test]
fn basic_fuchsia() {
    let cfg_str = r#"cfg(target_os = "fuchsia")"#;
    let output = cfg_to_gn_conditional(cfg_str).unwrap();
    assert_eq!(output, "current_os == \"fuchsia\"");
}

#[test]
fn conditonal_empty_any() {
    let cfg_str = r#"cfg(any())"#;
    let output = cfg_to_gn_conditional(cfg_str).unwrap();
    assert_eq!(output, "true");
}

#[test]
fn conditonal_any() {
    let cfg_str = r#"cfg(any(target_os = "fuchsia", target_os = "macos"))"#;
    let output = cfg_to_gn_conditional(cfg_str).unwrap();
    assert_eq!(output, "(current_os == \"fuchsia\" || current_os == \"mac\")");
}

#[test]
fn conditonal_all() {
    let cfg_str = r#"cfg(all(target_os = "fuchsia", target_os = "macos"))"#;
    let output = cfg_to_gn_conditional(cfg_str).unwrap();
    assert_eq!(output, "(current_os == \"fuchsia\" && current_os == \"mac\")");
}

#[test]
fn conditonal_all_not() {
    let cfg_str = r#"cfg(all(target_os = "fuchsia", not(target_os = "macos")))"#;
    let output = cfg_to_gn_conditional(cfg_str).unwrap();
    assert_eq!(output, "(current_os == \"fuchsia\" && !(current_os == \"mac\"))");
}

#[test]
fn conditonal_fail() {
    let cfg_str = r#"cfg(everything(target_os = "fuchsia"))"#;
    let output = cfg_to_gn_conditional(cfg_str).unwrap_err();
    assert_eq!(output.to_string(), r#"Unknown cfg option used: everything(target_os = "fuchsia")"#);
}

#[test]
fn nested_cfgs() {
    let cfg_str =
        r#"cfg(all(any(target_arch = "x86_64", target_arch = "aarch64"), target_os = "hermit"))"#;
    let output = cfg_to_gn_conditional(cfg_str).unwrap();
    assert_eq!(
        output.to_string(),
        r#"((current_cpu == "x64" || current_cpu == "arm64") && false)"#
    );
}

#[test]
fn target_cfg() {
    let target_str = r#"cfg(target_os = "fuchsia")"#;
    let output = target_to_gn_conditional(target_str).unwrap();
    assert_eq!(output, "current_os == \"fuchsia\"");
}

#[test]
fn target_full() {
    let target_str = r#"aarch64-apple-darwin"#;
    let output = target_to_gn_conditional(target_str).unwrap();
    assert_eq!(output, "(current_cpu == \"arm64\" && current_os == \"mac\")");
}

#[test]
fn target_unknown_full() {
    // We use a placeholder target "guaranteed" to never be used anywhere.
    let target_str = r#"foo-bar-baz"#;
    let err = target_to_gn_conditional(target_str).unwrap_err();
    assert_eq!(
        err.to_string(),
        "Unknown target: foo-bar-baz. Please add this to 'tools/cargo-gnaw/src/cfg.rs'.",
    );
}

#[test]
fn target_unknown_syntax() {
    // No leading "cfg", no hyphens.
    let target_str = r#"fizzbuzz"#;
    let err = target_to_gn_conditional(target_str).unwrap_err();
    assert_eq!(err.to_string(), "Unknown platform-specific dependency target syntax: fizzbuzz");
}