2 files changed, 86 insertions, 0 deletions

diff --git a/crates/stdx/Cargo.toml b/crates/stdx/Cargo.toml
new file mode 100644
index 000000000..f9e380c10
--- /dev/null
+++ b/crates/stdx/Cargo.toml
@@ -0,0 +1,11 @@
+[package]
+name = "stdx"
+version = "0.1.0"
+authors = ["rust-analyzer developers"]
+edition = "2018"
+
+[lib]
+doctest = false
+
+[dependencies]
+# Think twice before adding anything here
diff --git a/crates/stdx/src/lib.rs b/crates/stdx/src/lib.rs
new file mode 100644
index 000000000..8492c17af
--- /dev/null
+++ b/crates/stdx/src/lib.rs
@@ -0,0 +1,75 @@
+//! Missing batteries for standard libraries.
+
+use std::{cell::Cell, fmt};
+
+/// Appends formatted string to a `String`.
+#[macro_export]
+macro_rules! format_to {
+    (&buf:expr) => ();
+    ($buf:expr, $lit:literal $($arg:tt)*) => {
+        { use ::std::fmt::Write as _; let _ = ::std::write!($buf, $lit $($arg)*); }
+    };
+}
+
+pub trait SepBy: Sized {
+    /// Returns an `impl fmt::Display`, which joins elements via a separator.
+    fn sep_by<'a>(self, sep: &'a str) -> SepByBuilder<'a, Self>;
+}
+
+impl<I> SepBy for I
+where
+    I: Iterator,
+    I::Item: fmt::Display,
+{
+    fn sep_by<'a>(self, sep: &'a str) -> SepByBuilder<'a, Self> {
+        SepByBuilder::new(sep, self)
+    }
+}
+
+pub struct SepByBuilder<'a, I> {
+    sep: &'a str,
+    prefix: &'a str,
+    suffix: &'a str,
+    iter: Cell<Option<I>>,
+}
+
+impl<'a, I> SepByBuilder<'a, I> {
+    fn new(sep: &'a str, iter: I) -> SepByBuilder<'a, I> {
+        SepByBuilder { sep, prefix: "", suffix: "", iter: Cell::new(Some(iter)) }
+    }
+
+    pub fn prefix(mut self, prefix: &'a str) -> Self {
+        self.prefix = prefix;
+        self
+    }
+
+    pub fn suffix(mut self, suffix: &'a str) -> Self {
+        self.suffix = suffix;
+        self
+    }
+
+    /// Set both suffix and prefix.
+    pub fn surround_with(self, prefix: &'a str, suffix: &'a str) -> Self {
+        self.prefix(prefix).suffix(suffix)
+    }
+}
+
+impl<I> fmt::Display for SepByBuilder<'_, I>
+where
+    I: Iterator,
+    I::Item: fmt::Display,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(self.prefix)?;
+        let mut first = true;
+        for item in self.iter.take().unwrap() {
+            if !first {
+                f.write_str(self.sep)?;
+            }
+            first = false;
+            fmt::Display::fmt(&item, f)?;
+        }
+        f.write_str(self.suffix)?;
+        Ok(())
+    }
+}