4 files changed, 73 insertions, 0 deletions

diff --git a/xtask/src/codegen.rs b/xtask/src/codegen.rs
index 98acd7fa6..c468468de 100644
--- a/xtask/src/codegen.rs
+++ b/xtask/src/codegen.rs
@@ -9,6 +9,7 @@ mod gen_syntax;
 mod gen_parser_tests;
 mod gen_assists_docs;
 mod gen_feature_docs;
+mod gen_unstable_future_descriptor;
 
 use std::{
     fmt, mem,
@@ -26,8 +27,12 @@ pub use self::{
     gen_feature_docs::generate_feature_docs,
     gen_parser_tests::generate_parser_tests,
     gen_syntax::generate_syntax,
+    gen_unstable_future_descriptor::generate_unstable_future_descriptor,
 };
 
+// Directory used by xtask
+const STORAGE: &str = ".xtask";
+
 const GRAMMAR_DIR: &str = "crates/parser/src/grammar";
 const OK_INLINE_TESTS_DIR: &str = "crates/syntax/test_data/parser/inline/ok";
 const ERR_INLINE_TESTS_DIR: &str = "crates/syntax/test_data/parser/inline/err";
@@ -39,6 +44,10 @@ const AST_TOKENS: &str = "crates/syntax/src/ast/generated/tokens.rs";
 const ASSISTS_DIR: &str = "crates/assists/src/handlers";
 const ASSISTS_TESTS: &str = "crates/assists/src/tests/generated.rs";
 
+const REPOSITORY_URL: &str = "https://github.com/rust-lang/rust";
+const UNSTABLE_FEATURE: &str = "crates/ide/src/completion/unstable_feature_descriptor.rs";
+const REPO_PATH: &str = "src/doc/unstable-book/src";
+
 #[derive(Debug, PartialEq, Eq, Clone, Copy)]
 pub enum Mode {
     Overwrite,
diff --git a/xtask/src/codegen/gen_unstable_future_descriptor.rs b/xtask/src/codegen/gen_unstable_future_descriptor.rs
new file mode 100644
index 000000000..f220f85d3
--- /dev/null
+++ b/xtask/src/codegen/gen_unstable_future_descriptor.rs
@@ -0,0 +1,61 @@
+//! Generates descriptors structure for unstable feature from Unstable Book
+
+use crate::codegen::update;
+use crate::codegen::{self, project_root, Mode, Result};
+use crate::not_bash::{fs2, pushd, run};
+use proc_macro2::TokenStream;
+use quote::quote;
+use std::path::PathBuf;
+use walkdir::WalkDir;
+
+fn generate_descriptor(src_dir: PathBuf) -> Result<TokenStream> {
+    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().unwrap_or_default() == "md"
+        })
+        .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;
+
+        pub(crate) const UNSTABLE_FEATURE_DESCRIPTOR:  &[LintCompletion] = &[
+            #(#definitions),*
+        ];
+    };
+    Ok(ts)
+}
+
+pub fn generate_unstable_future_descriptor(mode: Mode) -> Result<()> {
+    let path = project_root().join(codegen::STORAGE);
+    fs2::create_dir_all(path.clone())?;
+
+    let _d = pushd(path.clone());
+    run!("git init")?;
+    run!("git remote add -f origin {}", codegen::REPOSITORY_URL)?;
+    run!("git pull origin master")?;
+
+    let src_dir = path.join(codegen::REPO_PATH);
+    let content = generate_descriptor(src_dir)?.to_string();
+
+    let contents = crate::reformat(content)?;
+    let destination = project_root().join(codegen::UNSTABLE_FEATURE);
+    update(destination.as_path(), &contents, mode)?;
+
+    Ok(())
+}
diff --git a/xtask/src/main.rs b/xtask/src/main.rs
index fb38fdc92..c4a15f4bd 100644
--- a/xtask/src/main.rs
+++ b/xtask/src/main.rs
@@ -77,6 +77,7 @@ FLAGS:
         "codegen" => {
             args.finish()?;
             codegen::generate_syntax(Mode::Overwrite)?;
+            codegen::generate_unstable_future_descriptor(Mode::Overwrite)?;
             codegen::generate_parser_tests(Mode::Overwrite)?;
             codegen::generate_assists_tests(Mode::Overwrite)?;
             codegen::generate_assists_docs(Mode::Overwrite)?;
diff --git a/xtask/tests/tidy.rs b/xtask/tests/tidy.rs
index ebd42cef7..bec3c630b 100644
--- a/xtask/tests/tidy.rs
+++ b/xtask/tests/tidy.rs
@@ -112,6 +112,8 @@ fn check_todo(path: &Path, text: &str) {
         // To support generating `todo!()` in assists, we have `expr_todo()` in
         // `ast::make`.
         "ast/make.rs",
+        // The documentation in string literals may contain anything for its own purposes
+        "completion/unstable_feature_descriptor.rs",
     ];
     if need_todo.iter().any(|p| path.ends_with(p)) {
         return;