1 files changed, 93 insertions, 0 deletions
diff --git a/src/tools/clippy/src/docs/map_err_ignore.txt b/src/tools/clippy/src/docs/map_err_ignore.txt
new file mode 100644
index 000000000..2606c13a7
--- /dev/null
+++ b/src/tools/clippy/src/docs/map_err_ignore.txt
@@ -0,0 +1,93 @@
+### What it does
+Checks for instances of `map_err(|_| Some::Enum)`
+
+### Why is this bad?
+This `map_err` throws away the original error rather than allowing the enum to contain and report the cause of the error
+
+### Example
+Before:
+```
+use std::fmt;
+
+#[derive(Debug)]
+enum Error {
+    Indivisible,
+    Remainder(u8),
+}
+
+impl fmt::Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Error::Indivisible => write!(f, "could not divide input by three"),
+            Error::Remainder(remainder) => write!(
+                f,
+                "input is not divisible by three, remainder = {}",
+                remainder
+            ),
+        }
+    }
+}
+
+impl std::error::Error for Error {}
+
+fn divisible_by_3(input: &str) -> Result<(), Error> {
+    input
+        .parse::<i32>()
+        .map_err(|_| Error::Indivisible)
+        .map(|v| v % 3)
+        .and_then(|remainder| {
+            if remainder == 0 {
+                Ok(())
+            } else {
+                Err(Error::Remainder(remainder as u8))
+            }
+        })
+}
+ ```
+
+ After:
+ ```rust
+use std::{fmt, num::ParseIntError};
+
+#[derive(Debug)]
+enum Error {
+    Indivisible(ParseIntError),
+    Remainder(u8),
+}
+
+impl fmt::Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Error::Indivisible(_) => write!(f, "could not divide input by three"),
+            Error::Remainder(remainder) => write!(
+                f,
+                "input is not divisible by three, remainder = {}",
+                remainder
+            ),
+        }
+    }
+}
+
+impl std::error::Error for Error {
+    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
+        match self {
+            Error::Indivisible(source) => Some(source),
+            _ => None,
+        }
+    }
+}
+
+fn divisible_by_3(input: &str) -> Result<(), Error> {
+    input
+        .parse::<i32>()
+        .map_err(Error::Indivisible)
+        .map(|v| v % 3)
+        .and_then(|remainder| {
+            if remainder == 0 {
+                Ok(())
+            } else {
+                Err(Error::Remainder(remainder as u8))
+            }
+        })
+}
+```
+\ No newline at end of file