add trim_split_whitespace

tests/ui/trim_split_whitespace.fixed

@@ -0,0 +1,91 @@
+// run-rustfix
+#![warn(clippy::trim_split_whitespace)]
+#![allow(clippy::let_unit_value)]
+
+struct Custom;
+impl Custom {
+    fn trim(self) -> Self {
+        self
+    }
+    fn split_whitespace(self) {}
+}
+
+struct DerefStr(&'static str);
+impl std::ops::Deref for DerefStr {
+    type Target = str;
+    fn deref(&self) -> &Self::Target {
+        self.0
+    }
+}
+
+struct DerefStrAndCustom(&'static str);
+impl std::ops::Deref for DerefStrAndCustom {
+    type Target = str;
+    fn deref(&self) -> &Self::Target {
+        self.0
+    }
+}
+impl DerefStrAndCustom {
+    fn trim(self) -> Self {
+        self
+    }
+    fn split_whitespace(self) {}
+}
+
+struct DerefStrAndCustomSplit(&'static str);
+impl std::ops::Deref for DerefStrAndCustomSplit {
+    type Target = str;
+    fn deref(&self) -> &Self::Target {
+        self.0
+    }
+}
+impl DerefStrAndCustomSplit {
+    #[allow(dead_code)]
+    fn split_whitespace(self) {}
+}
+
+struct DerefStrAndCustomTrim(&'static str);
+impl std::ops::Deref for DerefStrAndCustomTrim {
+    type Target = str;
+    fn deref(&self) -> &Self::Target {
+        self.0
+    }
+}
+impl DerefStrAndCustomTrim {
+    fn trim(self) -> Self {
+        self
+    }
+}
+
+fn main() {
+    // &str
+    let _ = " A B C ".split_whitespace(); // should trigger lint
+    let _ = " A B C ".split_whitespace(); // should trigger lint
+    let _ = " A B C ".split_whitespace(); // should trigger lint
+
+    // String
+    let _ = (" A B C ").to_string().split_whitespace(); // should trigger lint
+    let _ = (" A B C ").to_string().split_whitespace(); // should trigger lint
+    let _ = (" A B C ").to_string().split_whitespace(); // should trigger lint
+
+    // Custom
+    let _ = Custom.trim().split_whitespace(); // should not trigger lint
+
+    // Deref<Target=str>
+    let s = DerefStr(" A B C ");
+    let _ = s.split_whitespace(); // should trigger lint
+
+    // Deref<Target=str> + custom impl
+    let s = DerefStrAndCustom(" A B C ");
+    let _ = s.trim().split_whitespace(); // should not trigger lint
+
+    // Deref<Target=str> + only custom split_ws() impl
+    let s = DerefStrAndCustomSplit(" A B C ");
+    let _ = s.split_whitespace(); // should trigger lint
+    // Expl: trim() is called on str (deref) and returns &str.
+    //       Thus split_ws() is called on str as well and the custom impl on S is unused
+
+    // Deref<Target=str> + only custom trim() impl
+    let s = DerefStrAndCustomTrim(" A B C ");
+    let _ = s.trim().split_whitespace(); // should not trigger lint
+}

tests/ui/trim_split_whitespace.rs

@@ -0,0 +1,91 @@
+// run-rustfix
+#![warn(clippy::trim_split_whitespace)]
+#![allow(clippy::let_unit_value)]
+
+struct Custom;
+impl Custom {
+    fn trim(self) -> Self {
+        self
+    }
+    fn split_whitespace(self) {}
+}
+
+struct DerefStr(&'static str);
+impl std::ops::Deref for DerefStr {
+    type Target = str;
+    fn deref(&self) -> &Self::Target {
+        self.0
+    }
+}
+
+struct DerefStrAndCustom(&'static str);
+impl std::ops::Deref for DerefStrAndCustom {
+    type Target = str;
+    fn deref(&self) -> &Self::Target {
+        self.0
+    }
+}
+impl DerefStrAndCustom {
+    fn trim(self) -> Self {
+        self
+    }
+    fn split_whitespace(self) {}
+}
+
+struct DerefStrAndCustomSplit(&'static str);
+impl std::ops::Deref for DerefStrAndCustomSplit {
+    type Target = str;
+    fn deref(&self) -> &Self::Target {
+        self.0
+    }
+}
+impl DerefStrAndCustomSplit {
+    #[allow(dead_code)]
+    fn split_whitespace(self) {}
+}
+
+struct DerefStrAndCustomTrim(&'static str);
+impl std::ops::Deref for DerefStrAndCustomTrim {
+    type Target = str;
+    fn deref(&self) -> &Self::Target {
+        self.0
+    }
+}
+impl DerefStrAndCustomTrim {
+    fn trim(self) -> Self {
+        self
+    }
+}
+
+fn main() {
+    // &str
+    let _ = " A B C ".trim().split_whitespace(); // should trigger lint
+    let _ = " A B C ".trim_start().split_whitespace(); // should trigger lint
+    let _ = " A B C ".trim_end().split_whitespace(); // should trigger lint
+
+    // String
+    let _ = (" A B C ").to_string().trim().split_whitespace(); // should trigger lint
+    let _ = (" A B C ").to_string().trim_start().split_whitespace(); // should trigger lint
+    let _ = (" A B C ").to_string().trim_end().split_whitespace(); // should trigger lint
+
+    // Custom
+    let _ = Custom.trim().split_whitespace(); // should not trigger lint
+
+    // Deref<Target=str>
+    let s = DerefStr(" A B C ");
+    let _ = s.trim().split_whitespace(); // should trigger lint
+
+    // Deref<Target=str> + custom impl
+    let s = DerefStrAndCustom(" A B C ");
+    let _ = s.trim().split_whitespace(); // should not trigger lint
+
+    // Deref<Target=str> + only custom split_ws() impl
+    let s = DerefStrAndCustomSplit(" A B C ");
+    let _ = s.trim().split_whitespace(); // should trigger lint
+    // Expl: trim() is called on str (deref) and returns &str.
+    //       Thus split_ws() is called on str as well and the custom impl on S is unused
+
+    // Deref<Target=str> + only custom trim() impl
+    let s = DerefStrAndCustomTrim(" A B C ");
+    let _ = s.trim().split_whitespace(); // should not trigger lint
+}

tests/ui/trim_split_whitespace.stderr

@@ -0,0 +1,52 @@
+error: found call to `str::trim` before `str::split_whitespace`
+  --> $DIR/trim_split_whitespace.rs:62:23
+   |
+LL |     let _ = " A B C ".trim().split_whitespace(); // should trigger lint
+   |                       ^^^^^^^ help: remove `trim()`
+   |
+   = note: `-D clippy::trim-split-whitespace` implied by `-D warnings`
+
+error: found call to `str::trim_start` before `str::split_whitespace`
+  --> $DIR/trim_split_whitespace.rs:63:23
+   |
+LL |     let _ = " A B C ".trim_start().split_whitespace(); // should trigger lint
+   |                       ^^^^^^^^^^^^^ help: remove `trim_start()`
+
+error: found call to `str::trim_end` before `str::split_whitespace`
+  --> $DIR/trim_split_whitespace.rs:64:23
+   |
+LL |     let _ = " A B C ".trim_end().split_whitespace(); // should trigger lint
+   |                       ^^^^^^^^^^^ help: remove `trim_end()`
+
+error: found call to `str::trim` before `str::split_whitespace`
+  --> $DIR/trim_split_whitespace.rs:67:37
+   |
+LL |     let _ = (" A B C ").to_string().trim().split_whitespace(); // should trigger lint
+   |                                     ^^^^^^^ help: remove `trim()`
+
+error: found call to `str::trim_start` before `str::split_whitespace`
+  --> $DIR/trim_split_whitespace.rs:68:37
+   |
+LL |     let _ = (" A B C ").to_string().trim_start().split_whitespace(); // should trigger lint
+   |                                     ^^^^^^^^^^^^^ help: remove `trim_start()`
+
+error: found call to `str::trim_end` before `str::split_whitespace`
+  --> $DIR/trim_split_whitespace.rs:69:37
+   |
+LL |     let _ = (" A B C ").to_string().trim_end().split_whitespace(); // should trigger lint
+   |                                     ^^^^^^^^^^^ help: remove `trim_end()`
+
+error: found call to `str::trim` before `str::split_whitespace`
+  --> $DIR/trim_split_whitespace.rs:76:15
+   |
+LL |     let _ = s.trim().split_whitespace(); // should trigger lint
+   |               ^^^^^^^ help: remove `trim()`
+
+error: found call to `str::trim` before `str::split_whitespace`
+  --> $DIR/trim_split_whitespace.rs:84:15
+   |
+LL |     let _ = s.trim().split_whitespace(); // should trigger lint
+   |               ^^^^^^^ help: remove `trim()`
+
+error: aborting due to 8 previous errors
+