Auto merge of #4960 - ThibsG:patterns_with_wildcard_#4640, r=flip1995

New lint: pats_with_wild_match_arm

Wildcard use with other pattern in same match arm.

The wildcard covers other(s) pattern(s) as it will match anyway.

changelog: add new lint when multiple patterns (including wildcard) are used in a match arm.

Fixes #4640.

Author: bors

CHANGELOG.md

@@ -1361,6 +1361,7 @@ Released 2018-09-13
 [`while_let_on_iterator`]: https://rust-lang.github.io/rust-clippy/master/index.html#while_let_on_iterator
 [`wildcard_dependencies`]: https://rust-lang.github.io/rust-clippy/master/index.html#wildcard_dependencies
 [`wildcard_enum_match_arm`]: https://rust-lang.github.io/rust-clippy/master/index.html#wildcard_enum_match_arm
+[`wildcard_in_or_patterns`]: https://rust-lang.github.io/rust-clippy/master/index.html#wildcard_in_or_patterns
 [`write_literal`]: https://rust-lang.github.io/rust-clippy/master/index.html#write_literal
 [`write_with_newline`]: https://rust-lang.github.io/rust-clippy/master/index.html#write_with_newline
 [`writeln_empty_string`]: https://rust-lang.github.io/rust-clippy/master/index.html#writeln_empty_string

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 345 lints included in this crate!](https://rust-lang.github.io/rust-clippy/master/index.html)
+[There are 346 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_lints/src/lib.rs

@@ -600,6 +600,7 @@ pub fn register_plugins(store: &mut lint::LintStore, sess: &Session, conf: &Conf
         &matches::SINGLE_MATCH,
         &matches::SINGLE_MATCH_ELSE,
         &matches::WILDCARD_ENUM_MATCH_ARM,
+        &matches::WILDCARD_IN_OR_PATTERNS,
         &mem_discriminant::MEM_DISCRIMINANT_NON_ENUM,
         &mem_forget::MEM_FORGET,
         &mem_replace::MEM_REPLACE_OPTION_WITH_NONE,
@@ -1188,6 +1189,7 @@ pub fn register_plugins(store: &mut lint::LintStore, sess: &Session, conf: &Conf
         LintId::of(&matches::MATCH_REF_PATS),
         LintId::of(&matches::MATCH_WILD_ERR_ARM),
         LintId::of(&matches::SINGLE_MATCH),
+        LintId::of(&matches::WILDCARD_IN_OR_PATTERNS),
         LintId::of(&mem_discriminant::MEM_DISCRIMINANT_NON_ENUM),
         LintId::of(&mem_replace::MEM_REPLACE_OPTION_WITH_NONE),
         LintId::of(&mem_replace::MEM_REPLACE_WITH_DEFAULT),
@@ -1462,6 +1464,7 @@ pub fn register_plugins(store: &mut lint::LintStore, sess: &Session, conf: &Conf
         LintId::of(&map_unit_fn::OPTION_MAP_UNIT_FN),
         LintId::of(&map_unit_fn::RESULT_MAP_UNIT_FN),
         LintId::of(&matches::MATCH_AS_REF),
+        LintId::of(&matches::WILDCARD_IN_OR_PATTERNS),
         LintId::of(&methods::CHARS_NEXT_CMP),
         LintId::of(&methods::CLONE_ON_COPY),
         LintId::of(&methods::FILTER_NEXT),

clippy_lints/src/matches.rs

@@ -3,7 +3,8 @@ use crate::utils::paths;
 use crate::utils::sugg::Sugg;
 use crate::utils::{
     expr_block, is_allowed, is_expn_of, match_qpath, match_type, multispan_sugg, remove_blocks, snippet,
-    snippet_with_applicability, span_lint_and_sugg, span_lint_and_then, span_note_and_lint, walk_ptrs_ty,
+    snippet_with_applicability, span_help_and_lint, span_lint_and_sugg, span_lint_and_then, span_note_and_lint,
+    walk_ptrs_ty,
 };
 use if_chain::if_chain;
 use rustc::declare_lint_pass;
@@ -223,6 +224,26 @@ declare_clippy_lint! {
     "a wildcard enum match arm using `_`"
 }
 
+declare_clippy_lint! {
+    /// **What it does:** Checks for wildcard pattern used with others patterns in same match arm.
+    ///
+    /// **Why is this bad?** Wildcard pattern already covers any other pattern as it will match anyway.
+    /// It makes the code less readable, especially to spot wildcard pattern use in match arm.
+    ///
+    /// **Known problems:** None.
+    ///
+    /// **Example:**
+    /// ```rust
+    /// match "foo" {
+    ///     "a" => {},
+    ///     "bar" | _ => {},
+    /// }
+    /// ```
+    pub WILDCARD_IN_OR_PATTERNS,
+    complexity,
+    "a wildcard pattern used with others patterns in same match arm"
+}
+
 declare_lint_pass!(Matches => [
     SINGLE_MATCH,
     MATCH_REF_PATS,
@@ -231,7 +252,8 @@ declare_lint_pass!(Matches => [
     MATCH_OVERLAPPING_ARM,
     MATCH_WILD_ERR_ARM,
     MATCH_AS_REF,
-    WILDCARD_ENUM_MATCH_ARM
+    WILDCARD_ENUM_MATCH_ARM,
+    WILDCARD_IN_OR_PATTERNS
 ]);
 
 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Matches {
@@ -246,6 +268,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Matches {
             check_wild_err_arm(cx, ex, arms);
             check_wild_enum_match(cx, ex, arms);
             check_match_as_ref(cx, ex, arms, expr);
+            check_wild_in_or_pats(cx, arms);
         }
         if let ExprKind::Match(ref ex, ref arms, _) = expr.kind {
             check_match_ref_pats(cx, ex, arms, expr);
@@ -664,6 +687,23 @@ fn check_match_as_ref(cx: &LateContext<'_, '_>, ex: &Expr<'_>, arms: &[Arm<'_>],
     }
 }
 
+fn check_wild_in_or_pats(cx: &LateContext<'_, '_>, arms: &[Arm<'_>]) {
+    for arm in arms {
+        if let PatKind::Or(ref fields) = arm.pat.kind {
+            // look for multiple fields in this arm that contains at least one Wild pattern
+            if fields.len() > 1 && fields.iter().any(is_wild) {
+                span_help_and_lint(
+                    cx,
+                    WILDCARD_IN_OR_PATTERNS,
+                    arm.pat.span,
+                    "wildcard pattern covers any other pattern as it will match anyway.",
+                    "Consider handling `_` separately.",
+                );
+            }
+        }
+    }
+}
+
 /// Gets all arms that are unbounded `PatRange`s.
 fn all_ranges<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, arms: &'tcx [Arm<'_>]) -> Vec<SpannedRange<Constant>> {
     arms.iter()

src/lintlist/mod.rs

@@ -6,7 +6,7 @@ pub use lint::Lint;
 pub use lint::LINT_LEVELS;
 
 // begin lint list, do not remove this comment, it’s used in `update_lints`
-pub const ALL_LINTS: [Lint; 345] = [
+pub const ALL_LINTS: [Lint; 346] = [
     Lint {
         name: "absurd_extreme_comparisons",
         group: "correctness",
@@ -2345,6 +2345,13 @@ pub const ALL_LINTS: [Lint; 345] = [
         deprecation: None,
         module: "matches",
     },
+    Lint {
+        name: "wildcard_in_or_patterns",
+        group: "complexity",
+        desc: "a wildcard pattern used with others patterns in same match arm",
+        deprecation: None,
+        module: "matches",
+    },
     Lint {
         name: "write_literal",
         group: "style",

tests/ui/wild_in_or_pats.rs

@@ -0,0 +1,36 @@
+#![warn(clippy::wildcard_in_or_patterns)]
+
+fn main() {
+    match "foo" {
+        "a" => {
+            dbg!("matched a");
+        },
+        "bar" | _ => {
+            dbg!("matched (bar or) wild");
+        },
+    };
+    match "foo" {
+        "a" => {
+            dbg!("matched a");
+        },
+        "bar" | "bar2" | _ => {
+            dbg!("matched (bar or bar2 or) wild");
+        },
+    };
+    match "foo" {
+        "a" => {
+            dbg!("matched a");
+        },
+        _ | "bar" | _ => {
+            dbg!("matched (bar or) wild");
+        },
+    };
+    match "foo" {
+        "a" => {
+            dbg!("matched a");
+        },
+        _ | "bar" => {
+            dbg!("matched (bar or) wild");
+        },
+    };
+}

tests/ui/wild_in_or_pats.stderr

@@ -0,0 +1,35 @@
+error: wildcard pattern covers any other pattern as it will match anyway.
+  --> $DIR/wild_in_or_pats.rs:8:9
+   |
+LL |         "bar" | _ => {
+   |         ^^^^^^^^^
+   |
+   = note: `-D clippy::wildcard-in-or-patterns` implied by `-D warnings`
+   = help: Consider handling `_` separately.
+
+error: wildcard pattern covers any other pattern as it will match anyway.
+  --> $DIR/wild_in_or_pats.rs:16:9
+   |
+LL |         "bar" | "bar2" | _ => {
+   |         ^^^^^^^^^^^^^^^^^^
+   |
+   = help: Consider handling `_` separately.
+
+error: wildcard pattern covers any other pattern as it will match anyway.
+  --> $DIR/wild_in_or_pats.rs:24:9
+   |
+LL |         _ | "bar" | _ => {
+   |         ^^^^^^^^^^^^^
+   |
+   = help: Consider handling `_` separately.
+
+error: wildcard pattern covers any other pattern as it will match anyway.
+  --> $DIR/wild_in_or_pats.rs:32:9
+   |
+LL |         _ | "bar" => {
+   |         ^^^^^^^^^
+   |
+   = help: Consider handling `_` separately.
+
+error: aborting due to 4 previous errors
+

tests/ui/wildcard_enum_match_arm.fixed

@@ -1,7 +1,13 @@
 // run-rustfix
 
 #![deny(clippy::wildcard_enum_match_arm)]
-#![allow(unreachable_code, unused_variables, dead_code, clippy::single_match)]
+#![allow(
+    unreachable_code,
+    unused_variables,
+    dead_code,
+    clippy::single_match,
+    clippy::wildcard_in_or_patterns
+)]
 
 use std::io::ErrorKind;
 

tests/ui/wildcard_enum_match_arm.rs

@@ -1,7 +1,13 @@
 // run-rustfix
 
 #![deny(clippy::wildcard_enum_match_arm)]
-#![allow(unreachable_code, unused_variables, dead_code, clippy::single_match)]
+#![allow(
+    unreachable_code,
+    unused_variables,
+    dead_code,
+    clippy::single_match,
+    clippy::wildcard_in_or_patterns
+)]
 
 use std::io::ErrorKind;
 

tests/ui/wildcard_enum_match_arm.stderr

@@ -1,5 +1,5 @@
 error: wildcard match will miss any future added variants
-  --> $DIR/wildcard_enum_match_arm.rs:31:9
+  --> $DIR/wildcard_enum_match_arm.rs:37:9
    |
 LL |         _ => eprintln!("Not red"),
    |         ^ help: try this: `Color::Green | Color::Blue | Color::Rgb(..) | Color::Cyan`
@@ -11,25 +11,25 @@ LL | #![deny(clippy::wildcard_enum_match_arm)]
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: wildcard match will miss any future added variants
-  --> $DIR/wildcard_enum_match_arm.rs:35:9
+  --> $DIR/wildcard_enum_match_arm.rs:41:9
    |
 LL |         _not_red => eprintln!("Not red"),
    |         ^^^^^^^^ help: try this: `_not_red @ Color::Green | _not_red @ Color::Blue | _not_red @ Color::Rgb(..) | _not_red @ Color::Cyan`
 
 error: wildcard match will miss any future added variants
-  --> $DIR/wildcard_enum_match_arm.rs:39:9
+  --> $DIR/wildcard_enum_match_arm.rs:45:9
    |
 LL |         not_red => format!("{:?}", not_red),
    |         ^^^^^^^ help: try this: `not_red @ Color::Green | not_red @ Color::Blue | not_red @ Color::Rgb(..) | not_red @ Color::Cyan`
 
 error: wildcard match will miss any future added variants
-  --> $DIR/wildcard_enum_match_arm.rs:55:9
+  --> $DIR/wildcard_enum_match_arm.rs:61:9
    |
 LL |         _ => "No red",
    |         ^ help: try this: `Color::Red | Color::Green | Color::Blue | Color::Rgb(..) | Color::Cyan`
 
 error: match on non-exhaustive enum doesn't explicitly match all known variants
-  --> $DIR/wildcard_enum_match_arm.rs:72:9
+  --> $DIR/wildcard_enum_match_arm.rs:78:9
    |
 LL |         _ => {},
    |         ^ help: try this: `std::io::ErrorKind::PermissionDenied | std::io::ErrorKind::ConnectionRefused | std::io::ErrorKind::ConnectionReset | std::io::ErrorKind::ConnectionAborted | std::io::ErrorKind::NotConnected | std::io::ErrorKind::AddrInUse | std::io::ErrorKind::AddrNotAvailable | std::io::ErrorKind::BrokenPipe | std::io::ErrorKind::AlreadyExists | std::io::ErrorKind::WouldBlock | std::io::ErrorKind::InvalidInput | std::io::ErrorKind::InvalidData | std::io::ErrorKind::TimedOut | std::io::ErrorKind::WriteZero | std::io::ErrorKind::Interrupted | std::io::ErrorKind::Other | std::io::ErrorKind::UnexpectedEof | _`