feat(build): add rustc check

src/build.rs

@@ -3,10 +3,57 @@
 use emoji;
 use error::Error;
 use progressbar::Step;
+use std::env;
 use std::path::Path;
 use std::process::Command;
+use std::str;
 use PBAR;
 
+/// Ensure that `rustc` is present and that it is >= 1.30.0
+pub fn check_rustc_version(step: &Step) -> Result<String, Error> {
+    let msg = format!("{}Checking `rustc` version...", emoji::TARGET);
+    PBAR.step(step, &msg);
+    let local_minor_version = rustc_minor_version();
+    match local_minor_version {
+        Some(mv) => {
+            if mv < 30 {
+              return Err(Error::RustcVersion {
+                message: format!(
+                  "Your version of Rust, '{}', is not supported.",
+                  mv.to_string()
+                ),
+                local_minor_version: mv.to_string(),
+              })
+            } else {
+              Ok(mv.to_string())
+            }
+      },
+      None => Err(Error::RustcMissing {
+        message: "We can't figure out what your Rust version is- which means you might not have Rust ins    talled. Please install Rust version 1.30.0 or higher.".to_string(),
+      }),
+    }
+}
+
+// from https://github.com/alexcrichton/proc-macro2/blob/79e40a113b51836f33214c6d00228934b41bd4ad/build.rs#L44-L61
+fn rustc_minor_version() -> Option<u32> {
+    macro_rules! otry {
+        ($e:expr) => {
+            match $e {
+                Some(e) => e,
+                None => return None,
+            }
+        };
+    }
+    let rustc = otry!(env::var_os("RUSTC"));
+    let output = otry!(Command::new(rustc).arg("--version").output().ok());
+    let version = otry!(str::from_utf8(&output.stdout).ok());
+    let mut pieces = version.split('.');
+    if pieces.next() != Some("rustc 1") {
+        return None;
+    }
+    otry!(pieces.next()).parse().ok()
+}
+
 /// Ensure that `rustup` has the `wasm32-unknown-unknown` target installed for
 /// the `nightly` toolchain.
 pub fn rustup_add_wasm_target(step: &Step) -> Result<(), Error> {

src/command/build.rs

@@ -156,6 +156,7 @@ impl Build {
         }
         match &mode {
             BuildMode::Normal => steps![
+                step_check_rustc_version,
                 step_check_crate_config,
                 step_add_wasm_target,
                 step_build_wasm,
@@ -166,6 +167,7 @@ impl Build {
                 step_run_wasm_bindgen,
             ],
             BuildMode::Noinstall => steps![
+                step_check_rustc_version,
                 step_check_crate_config,
                 step_build_wasm,
                 step_create_dir,
@@ -176,6 +178,14 @@ impl Build {
         }
     }
 
+    fn step_check_rustc_version(&mut self, step: &Step, log: &Logger) -> Result<(), Error> {
+        info!(&log, "Checking rustc version...");
+        let version = build::check_rustc_version(step)?;
+        let msg = format!("rustc version is {}.", version);
+        info!(&log, "{}", &msg);
+        Ok(())
+    }
+
     fn step_check_crate_config(&mut self, step: &Step, log: &Logger) -> Result<(), Error> {
         info!(&log, "Checking crate configuration...");
         manifest::check_crate_config(&self.crate_path, step)?;

src/error.rs

@@ -29,6 +29,22 @@ pub enum Error {
     /// An error handling zip archives.
     Zip(#[cause] zip::result::ZipError),
 
+    #[fail(display = "{}", _0)]
+    /// An error in parsing your rustc version.
+    RustcMissing {
+        /// Error message
+        message: String,
+    },
+
+    #[fail(display = "{}", _0)]
+    /// An error from having an unsupported rustc version.
+    RustcVersion {
+        /// Error message
+        message: String,
+        /// The minor version of the local rust
+        local_minor_version: String,
+    },
+
     /// An error invoking another CLI tool.
     #[fail(display = "{}. stderr:\n\n{}", message, stderr)]
     Cli {
@@ -112,6 +128,14 @@ impl Error {
         }
     }
 
+    /// Construct a rustc version error.
+    pub fn rustc_version_error(message: &str, local_version: &str) -> Self {
+        Error::RustcVersion {
+            message: message.to_string(),
+            local_minor_version: local_version.to_string(),
+        }
+    }
+
     /// Get a string description of this error's type.
     pub fn error_type(&self) -> String {
         match self {
@@ -119,6 +143,13 @@ impl Error {
             Error::SerdeJson(_) => "There was an JSON error. Details:\n\n",
             Error::SerdeToml(_) => "There was an TOML error. Details:\n\n",
             Error::Zip(_) => "There was an error handling zip files. Details:\n\n",
+            Error::RustcMissing {
+              message: _,
+            } =>  "We can't figure out what your Rust version is- which means you might not have Rust installed. Please install Rust version 1.30.0 or higher.",
+            Error::RustcVersion {
+              message: _,
+              local_minor_version: _,
+            } => "Your rustc version is not supported. Please install version 1.30.0 or higher.",
             Error::Cli {
                 message: _,
                 stderr: _,