new lint for missing #[must_use] on pure fns

Author: llogiq

CHANGELOG.md

@@ -1116,6 +1116,7 @@ Released 2018-09-13
 [`ptr_arg`]: https://rust-lang.github.io/rust-clippy/master/index.html#ptr_arg
 [`ptr_offset_with_cast`]: https://rust-lang.github.io/rust-clippy/master/index.html#ptr_offset_with_cast
 [`pub_enum_variant_names`]: https://rust-lang.github.io/rust-clippy/master/index.html#pub_enum_variant_names
+[`pure_without_must_use`]: https://rust-lang.github.io/rust-clippy/master/index.html#pure_without_must_use
 [`question_mark`]: https://rust-lang.github.io/rust-clippy/master/index.html#question_mark
 [`range_minus_one`]: https://rust-lang.github.io/rust-clippy/master/index.html#range_minus_one
 [`range_plus_one`]: https://rust-lang.github.io/rust-clippy/master/index.html#range_plus_one

README.md

@@ -6,7 +6,7 @@
 
 A collection of lints to catch common mistakes and improve your [Rust](https://github.com/rust-lang/rust) code.
 
-[There are 315 lints included in this crate!](https://rust-lang.github.io/rust-clippy/master/index.html)
+[There are 316 lints included in this crate!](https://rust-lang.github.io/rust-clippy/master/index.html)
 
 We have a bunch of lint categories to allow you to choose how much Clippy is supposed to ~~annoy~~ help you:
 

clippy_dev/src/fmt.rs

@@ -134,6 +134,7 @@ fn exec(
     Ok(success)
 }
 
+#[must_use]
 fn cargo_fmt(context: &FmtContext, path: &Path) -> Result<bool, CliError> {
     let mut args = vec!["+nightly", "fmt", "--all"];
     if context.check {
@@ -145,6 +146,7 @@ fn cargo_fmt(context: &FmtContext, path: &Path) -> Result<bool, CliError> {
     Ok(success)
 }
 
+#[must_use]
 fn rustfmt_test(context: &FmtContext) -> Result<(), CliError> {
     let program = "rustfmt";
     let dir = std::env::current_dir()?;
@@ -168,6 +170,7 @@ fn rustfmt_test(context: &FmtContext) -> Result<(), CliError> {
     }
 }
 
+#[must_use]
 fn rustfmt(context: &FmtContext, path: &Path) -> Result<bool, CliError> {
     let mut args = vec!["+nightly".as_ref(), path.as_os_str()];
     if context.check {

clippy_dev/src/lib.rs

@@ -137,6 +137,7 @@ pub fn gen_deprecated(lints: &[Lint]) -> Vec<String> {
 }
 
 /// Gathers all files in `src/clippy_lints` and gathers all lints inside
+#[must_use]
 pub fn gather_all() -> impl Iterator<Item = Lint> {
     lint_files().flat_map(|f| gather_from_file(&f))
 }
@@ -161,6 +162,7 @@ fn gather_from_file(dir_entry: &walkdir::DirEntry) -> impl Iterator<Item = Lint>
     parse_contents(&content, filename)
 }
 
+#[must_use]
 fn parse_contents(content: &str, filename: &str) -> impl Iterator<Item = Lint> {
     let lints = DEC_CLIPPY_LINT_RE
         .captures_iter(content)
@@ -173,6 +175,7 @@ fn parse_contents(content: &str, filename: &str) -> impl Iterator<Item = Lint> {
 }
 
 /// Collects all .rs files in the `clippy_lints/src` directory
+#[must_use]
 fn lint_files() -> impl Iterator<Item = walkdir::DirEntry> {
     // We use `WalkDir` instead of `fs::read_dir` here in order to recurse into subdirectories.
     // Otherwise we would not collect all the lints, for example in `clippy_lints/src/methods/`.

clippy_dev/src/stderr_length_check.rs

@@ -34,6 +34,7 @@ fn exceeding_stderr_files(files: impl Iterator<Item = walkdir::DirEntry>) -> imp
     })
 }
 
+#[must_use]
 fn stderr_files() -> impl Iterator<Item = walkdir::DirEntry> {
     // We use `WalkDir` instead of `fs::read_dir` here in order to recurse into subdirectories.
     WalkDir::new("../tests/ui")
@@ -42,6 +43,7 @@ fn stderr_files() -> impl Iterator<Item = walkdir::DirEntry> {
         .filter(|f| f.path().extension() == Some(OsStr::new("stderr")))
 }
 
+#[must_use]
 fn count_linenumbers(filepath: &str) -> usize {
     if let Ok(mut file) = File::open(filepath) {
         let mut content = String::new();

clippy_lints/src/approx_const.rs

@@ -93,6 +93,7 @@ fn check_known_consts(cx: &LateContext<'_, '_>, e: &Expr, s: symbol::Symbol, mod
 /// Returns `false` if the number of significant figures in `value` are
 /// less than `min_digits`; otherwise, returns true if `value` is equal
 /// to `constant`, rounded to the number of digits present in `value`.
+#[must_use]
 fn is_approx_const(constant: f64, value: &str, min_digits: usize) -> bool {
     if value.len() <= min_digits {
         false

clippy_lints/src/assign_ops.rs

@@ -229,6 +229,7 @@ fn lint_misrefactored_assign_op(
     );
 }
 
+#[must_use]
 fn is_commutative(op: hir::BinOpKind) -> bool {
     use rustc::hir::BinOpKind::*;
     match op {

clippy_lints/src/bit_mask.rs

@@ -100,6 +100,7 @@ pub struct BitMask {
 }
 
 impl BitMask {
+    #[must_use]
     pub fn new(verbose_bit_mask_threshold: u64) -> Self {
         Self {
             verbose_bit_mask_threshold,
@@ -150,6 +151,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for BitMask {
     }
 }
 
+#[must_use]
 fn invert_cmp(cmp: BinOpKind) -> BinOpKind {
     match cmp {
         BinOpKind::Eq => BinOpKind::Eq,

clippy_lints/src/checked_conversions.rs

@@ -160,6 +160,7 @@ impl<'a> Conversion<'a> {
 
 impl ConversionType {
     /// Creates a conversion type if the type is allowed & conversion is valid
+    #[must_use]
     fn try_new(from: &str, to: &str) -> Option<Self> {
         if UINTS.contains(&from) {
             Some(Self::FromUnsigned)

clippy_lints/src/cognitive_complexity.rs

@@ -29,6 +29,7 @@ pub struct CognitiveComplexity {
 }
 
 impl CognitiveComplexity {
+    #[must_use]
     pub fn new(limit: u64) -> Self {
         Self {
             limit: LimitStack::new(limit),