1 files changed, 113 insertions, 0 deletions
diff --git a/third_party/rust/sql-support/src/repeat.rs b/third_party/rust/sql-support/src/repeat.rs
new file mode 100644
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+++ b/third_party/rust/sql-support/src/repeat.rs
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+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use std::fmt;
+
+/// Helper type for printing repeated strings more efficiently. You should use
+/// [`repeat_display`](sql_support::repeat_display), or one of the `repeat_sql_*` helpers to
+/// construct it.
+#[derive(Debug, Clone)]
+pub struct RepeatDisplay<'a, F> {
+    count: usize,
+    sep: &'a str,
+    fmt_one: F,
+}
+
+impl<'a, F> fmt::Display for RepeatDisplay<'a, F>
+where
+    F: Fn(usize, &mut fmt::Formatter<'_>) -> fmt::Result,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        for i in 0..self.count {
+            if i != 0 {
+                f.write_str(self.sep)?;
+            }
+            (self.fmt_one)(i, f)?;
+        }
+        Ok(())
+    }
+}
+
+/// Construct a RepeatDisplay that will repeatedly call `fmt_one` with a formatter `count` times,
+/// separated by `sep`.
+///
+/// # Example
+///
+/// ```rust
+/// # use sql_support::repeat_display;
+/// assert_eq!(format!("{}", repeat_display(1, ",", |i, f| write!(f, "({},?)", i))),
+///            "(0,?)");
+/// assert_eq!(format!("{}", repeat_display(2, ",", |i, f| write!(f, "({},?)", i))),
+///            "(0,?),(1,?)");
+/// assert_eq!(format!("{}", repeat_display(3, ",", |i, f| write!(f, "({},?)", i))),
+///            "(0,?),(1,?),(2,?)");
+/// ```
+#[inline]
+pub fn repeat_display<F>(count: usize, sep: &str, fmt_one: F) -> RepeatDisplay<'_, F>
+where
+    F: Fn(usize, &mut fmt::Formatter<'_>) -> fmt::Result,
+{
+    RepeatDisplay {
+        count,
+        sep,
+        fmt_one,
+    }
+}
+
+/// Returns a value that formats as `count` instances of `?` separated by commas.
+///
+/// # Example
+///
+/// ```rust
+/// # use sql_support::repeat_sql_vars;
+/// assert_eq!(format!("{}", repeat_sql_vars(0)), "");
+/// assert_eq!(format!("{}", repeat_sql_vars(1)), "?");
+/// assert_eq!(format!("{}", repeat_sql_vars(2)), "?,?");
+/// assert_eq!(format!("{}", repeat_sql_vars(3)), "?,?,?");
+/// ```
+pub fn repeat_sql_vars(count: usize) -> impl fmt::Display {
+    repeat_display(count, ",", |_, f| write!(f, "?"))
+}
+
+/// Returns a value that formats as `count` instances of `(?)` separated by commas.
+///
+/// # Example
+///
+/// ```rust
+/// # use sql_support::repeat_sql_values;
+/// assert_eq!(format!("{}", repeat_sql_values(0)), "");
+/// assert_eq!(format!("{}", repeat_sql_values(1)), "(?)");
+/// assert_eq!(format!("{}", repeat_sql_values(2)), "(?),(?)");
+/// assert_eq!(format!("{}", repeat_sql_values(3)), "(?),(?),(?)");
+/// ```
+///
+pub fn repeat_sql_values(count: usize) -> impl fmt::Display {
+    // We could also implement this as `repeat_sql_multi_values(count, 1)`,
+    // but this is faster and no less clear IMO.
+    repeat_display(count, ",", |_, f| write!(f, "(?)"))
+}
+
+/// Returns a value that formats as `num_values` instances of `(?,?,?,...)` (where there are
+/// `vars_per_value` question marks separated by commas in between the `?`s).
+///
+/// Panics if `vars_per_value` is zero (however, `num_values` is allowed to be zero).
+///
+/// # Example
+///
+/// ```rust
+/// # use sql_support::repeat_multi_values;
+/// assert_eq!(format!("{}", repeat_multi_values(0, 2)), "");
+/// assert_eq!(format!("{}", repeat_multi_values(1, 5)), "(?,?,?,?,?)");
+/// assert_eq!(format!("{}", repeat_multi_values(2, 3)), "(?,?,?),(?,?,?)");
+/// assert_eq!(format!("{}", repeat_multi_values(3, 1)), "(?),(?),(?)");
+/// ```
+pub fn repeat_multi_values(num_values: usize, vars_per_value: usize) -> impl fmt::Display {
+    assert_ne!(
+        vars_per_value, 0,
+        "Illegal value for `vars_per_value`, must not be zero"
+    );
+    repeat_display(num_values, ",", move |_, f| {
+        write!(f, "({})", repeat_sql_vars(vars_per_value))
+    })
+}