Auto merge of #10534 - samueltardieu:lines-filter-map-ok, r=llogiq

Flag `bufreader.lines().filter_map(Result::ok)` as suspicious

This lint detects a problem that happened recently in https://github.com/uutils/coreutils and is described in https://github.com/rust-lang/rust/issues/64144.

changelog: [`lines_filter_map_ok`]: new lint

tests/ui/lines_filter_map_ok.fixed

@@ -0,0 +1,29 @@
+// run-rustfix
+
+#![allow(unused, clippy::map_identity)]
+#![warn(clippy::lines_filter_map_ok)]
+
+use std::io::{self, BufRead, BufReader};
+
+fn main() -> io::Result<()> {
+    let f = std::fs::File::open("/")?;
+    // Lint
+    BufReader::new(f).lines().map_while(Result::ok).for_each(|_| ());
+    // Lint
+    let f = std::fs::File::open("/")?;
+    BufReader::new(f).lines().map_while(Result::ok).for_each(|_| ());
+    let s = "foo\nbar\nbaz\n";
+    // Lint
+    io::stdin().lines().map_while(Result::ok).for_each(|_| ());
+    // Lint
+    io::stdin().lines().map_while(Result::ok).for_each(|_| ());
+    // Do not lint (not a `Lines` iterator)
+    io::stdin()
+        .lines()
+        .map(std::convert::identity)
+        .filter_map(|x| x.ok())
+        .for_each(|_| ());
+    // Do not lint (not a `Result::ok()` extractor)
+    io::stdin().lines().filter_map(|x| x.err()).for_each(|_| ());
+    Ok(())
+}

tests/ui/lines_filter_map_ok.rs

@@ -0,0 +1,29 @@
+// run-rustfix
+
+#![allow(unused, clippy::map_identity)]
+#![warn(clippy::lines_filter_map_ok)]
+
+use std::io::{self, BufRead, BufReader};
+
+fn main() -> io::Result<()> {
+    let f = std::fs::File::open("/")?;
+    // Lint
+    BufReader::new(f).lines().filter_map(Result::ok).for_each(|_| ());
+    // Lint
+    let f = std::fs::File::open("/")?;
+    BufReader::new(f).lines().flat_map(Result::ok).for_each(|_| ());
+    let s = "foo\nbar\nbaz\n";
+    // Lint
+    io::stdin().lines().filter_map(Result::ok).for_each(|_| ());
+    // Lint
+    io::stdin().lines().filter_map(|x| x.ok()).for_each(|_| ());
+    // Do not lint (not a `Lines` iterator)
+    io::stdin()
+        .lines()
+        .map(std::convert::identity)
+        .filter_map(|x| x.ok())
+        .for_each(|_| ());
+    // Do not lint (not a `Result::ok()` extractor)
+    io::stdin().lines().filter_map(|x| x.err()).for_each(|_| ());
+    Ok(())
+}

tests/ui/lines_filter_map_ok.stderr

@@ -0,0 +1,51 @@
+error: `filter_map()` will run forever if the iterator repeatedly produces an `Err`
+  --> $DIR/lines_filter_map_ok.rs:11:31
+   |
+LL |     BufReader::new(f).lines().filter_map(Result::ok).for_each(|_| ());
+   |                               ^^^^^^^^^^^^^^^^^^^^^^ help: replace with: `map_while(Result::ok)`
+   |
+note: this expression returning a `std::io::Lines` may produce an infinite number of `Err` in case of a read error
+  --> $DIR/lines_filter_map_ok.rs:11:5
+   |
+LL |     BufReader::new(f).lines().filter_map(Result::ok).for_each(|_| ());
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^
+   = note: `-D clippy::lines-filter-map-ok` implied by `-D warnings`
+
+error: `flat_map()` will run forever if the iterator repeatedly produces an `Err`
+  --> $DIR/lines_filter_map_ok.rs:14:31
+   |
+LL |     BufReader::new(f).lines().flat_map(Result::ok).for_each(|_| ());
+   |                               ^^^^^^^^^^^^^^^^^^^^ help: replace with: `map_while(Result::ok)`
+   |
+note: this expression returning a `std::io::Lines` may produce an infinite number of `Err` in case of a read error
+  --> $DIR/lines_filter_map_ok.rs:14:5
+   |
+LL |     BufReader::new(f).lines().flat_map(Result::ok).for_each(|_| ());
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: `filter_map()` will run forever if the iterator repeatedly produces an `Err`
+  --> $DIR/lines_filter_map_ok.rs:17:25
+   |
+LL |     io::stdin().lines().filter_map(Result::ok).for_each(|_| ());
+   |                         ^^^^^^^^^^^^^^^^^^^^^^ help: replace with: `map_while(Result::ok)`
+   |
+note: this expression returning a `std::io::Lines` may produce an infinite number of `Err` in case of a read error
+  --> $DIR/lines_filter_map_ok.rs:17:5
+   |
+LL |     io::stdin().lines().filter_map(Result::ok).for_each(|_| ());
+   |     ^^^^^^^^^^^^^^^^^^^
+
+error: `filter_map()` will run forever if the iterator repeatedly produces an `Err`
+  --> $DIR/lines_filter_map_ok.rs:19:25
+   |
+LL |     io::stdin().lines().filter_map(|x| x.ok()).for_each(|_| ());
+   |                         ^^^^^^^^^^^^^^^^^^^^^^ help: replace with: `map_while(Result::ok)`
+   |
+note: this expression returning a `std::io::Lines` may produce an infinite number of `Err` in case of a read error
+  --> $DIR/lines_filter_map_ok.rs:19:5
+   |
+LL |     io::stdin().lines().filter_map(|x| x.ok()).for_each(|_| ());
+   |     ^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 4 previous errors
+