Added competition for unstable features

Added xtask for download unstable book from rust repository and codegene for it. Also small changes from lint

xtask/src/codegen/gen_unstable_future_descriptor.rs

@@ -0,0 +1,55 @@
+//! Generates descriptors structure for unstable feature from Unstable Book
+
+use crate::{
+    codegen::{self, project_root, Mode, Result},
+};
+use std::process::Command;
+use std::fs;
+use std::path::{Path, PathBuf};
+use walkdir::{DirEntry, WalkDir};
+use quote::{format_ident, quote};
+use crate::codegen::update;
+
+pub fn generate_unstable_future_descriptor(mode: Mode) -> Result<()> {
+    let path = project_root().join(codegen::STORAGE);
+    fs::create_dir_all(path.clone())?;
+
+    Command::new("git").current_dir(path.clone()).arg("init").output()?;
+    Command::new("git").current_dir(path.clone()).args(&["remote", "add", "-f", "origin", codegen::REPOSITORY_URL]).output()?;
+    Command::new("git").current_dir(path.clone()).args(&["sparse-checkout", "set", "/src/doc/unstable-book/src/"]).output()?;
+    Command::new("git").current_dir(path.clone()).args(&["pull", "origin", "master"]).output()?;
+    //TODO: check git, and do pull 
+
+    let src_dir = path.join("src/doc/unstable-book/src");
+    let files = WalkDir::new(src_dir.join("language-features"))
+        .into_iter()
+        .chain(WalkDir::new(src_dir.join("library-features")))
+        .filter_map(|e| e.ok())
+        .filter(|entry| {
+            // Get all `.md ` files
+            entry.file_type().is_file() && entry.path().extension().map(|ext| ext == "md").unwrap_or(false)
+        })
+        .collect::<Vec<_>>();
+
+    let definitions = files.iter().map(|entry| {
+        let path = entry.path();
+        let feature_ident = format!("{}", path.file_stem().unwrap().to_str().unwrap().replace("-", "_"));
+        let doc = format!("{}", std::fs::read_to_string(path).unwrap() );
+       
+        quote!{ LintCompletion { label: #feature_ident, description: #doc } }
+    }).collect::<Vec<_>>();
+    
+    let ts = quote! {
+        use crate::completion::LintCompletion;
+
+        const UNSTABLE_FEATURE_DESCRIPTOR:  &[LintCompletion] = &[
+            #(#definitions),*
+        ];
+    };
+    
+    let destination = project_root().join(codegen::UNSTABLE_FEATURE);
+    let contents = crate::reformat(ts.to_string())?;
+    update(destination.as_path(), &contents, mode)?;
+
+    Ok(())
+}