Add postfix match support & UI tests

Author: RossSmyth

src/tools/clippy/clippy_lints/src/matches/mod.rs

@@ -1053,7 +1053,7 @@ impl<'tcx> LateLintPass<'tcx> for Matches {
             }
 
             if !from_expansion && !contains_cfg_arm(cx, expr, ex, arms) {
-                if source == MatchSource::Normal {
+                if let MatchSource::Normal | MatchSource::Postfix = source  {
                     if !(self.msrv.meets(msrvs::MATCHES_MACRO) && match_like_matches::check_match(cx, expr, ex, arms)) {
                         match_same_arms::check(cx, arms);
                     }

src/tools/clippy/tests/ui/postfix_match.fixed

@@ -0,0 +1,62 @@
+#![feature(postfix_match)]
+#![allow(clippy::redundant_at_rest_pattern, clippy::useless_vec)]
+#![warn(
+    clippy::match_on_vec_items, 
+    clippy::single_match, 
+    clippy::match_bool, 
+    clippy::match_as_ref,
+    clippy::needless_match,
+    clippy::match_str_case_mismatch,
+    clippy::redundant_guards
+)]
+
+fn main() {
+    // match_on_vec_items
+    let arr = vec![0, 1, 2, 3];
+    let idx = 1;
+
+    arr.get(idx).match {
+        //~^ ERROR: indexing into a vector may panic
+        //~| NOTE: `-D clippy::match-on-vec-items` implied by `-D warnings`
+        0 => println!("{}", 0),
+        1 => println!("{}", 3),
+        _ => {},
+    };
+
+    // single_match
+    let x = Some(1u8);
+
+    if let Some(y) = x {
+        println!("{:?}", y);
+    };
+
+    // match_bool
+    let test: bool = true;
+
+    if test { 0 } else { 42 };
+
+    // match_as_ref
+    let owned: Option<()> = None;
+    let borrowed: Option<&()> = owned.as_ref();
+
+    // needless_match
+    let i = 10;
+    let _: i32 =  i;
+
+    // match_str_case_mismatch
+    let var = "BAR";
+    var.to_ascii_lowercase().as_str().match {
+        "foo" => {},
+        "bar" => {},
+        _ => {},
+    }
+
+    // redundant_guards
+    struct C(u32, u32);
+
+    let c = C(1, 2);
+    c.match {
+        C(x, 1) => ..,
+        _ => todo!(),
+    };
+}

src/tools/clippy/tests/ui/postfix_match.rs

@@ -0,0 +1,77 @@
+#![feature(postfix_match)]
+#![allow(clippy::redundant_at_rest_pattern, clippy::useless_vec)]
+#![warn(
+    clippy::match_on_vec_items, 
+    clippy::single_match, 
+    clippy::match_bool, 
+    clippy::match_as_ref,
+    clippy::needless_match,
+    clippy::match_str_case_mismatch,
+    clippy::redundant_guards
+)]
+
+fn main() {
+    // match_on_vec_items
+    let arr = vec![0, 1, 2, 3];
+    let idx = 1;
+
+    arr[idx].match {
+        //~^ ERROR: indexing into a vector may panic
+        //~| NOTE: `-D clippy::match-on-vec-items` implied by `-D warnings`
+        0 => println!("{}", 0),
+        1 => println!("{}", 3),
+        _ => {},
+    };
+
+    // single_match
+    let x = Some(1u8);
+
+    x.match {
+        Some(y) => {
+            println!("{:?}", y);
+        },
+        _ => (),
+    };
+
+    // match_bool
+    let test: bool = true;
+
+    test.match {
+        //~^ ERROR: you seem to be trying to match on a boolean expression
+        true => 0,
+        false => 42,
+    };
+
+    // match_as_ref
+    let owned: Option<()> = None;
+    let borrowed: Option<&()> = owned.match {
+        None => None,
+        Some(ref v) => Some(v),
+    };
+
+    // needless_match
+    let i = 10;
+    let _: i32 =  i.match {
+        0 => 0,
+        1 => 1,
+        2 => 2,
+        _ => i,
+    };
+
+    // match_str_case_mismatch
+    let var = "BAR";
+    var.to_ascii_lowercase().as_str().match {
+        "foo" => {},
+        "bar" => {},
+        _ => {},
+    }
+
+    // redundant_guards
+    struct C(u32, u32);
+
+    let c = C(1, 2);
+    c.match {
+        C(x, y) if 1 == y => ..,
+        _ => todo!(),
+    };
+}

src/tools/clippy/tests/ui/postfix_match.stderr

@@ -0,0 +1,86 @@
+error: indexing into a vector may panic
+  --> $DIR/postfix_match.rs:18:5
+   |
+LL |     arr[idx].match {
+   |     ^^^^^^^^ help: try: `arr.get(idx)`
+   |
+   = note: `-D clippy::match-on-vec-items` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::match_on_vec_items)]`
+
+error: you seem to be trying to use `match` for destructuring a single pattern. Consider using `if let`
+  --> $DIR/postfix_match.rs:29:5
+   |
+LL | /     x.match {
+LL | |         Some(y) => {
+LL | |             println!("{:?}", y);
+LL | |         },
+LL | |         _ => (),
+LL | |     };
+   | |_____^
+   |
+   = note: `-D clippy::single-match` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::single_match)]`
+help: try
+   |
+LL ~     if let Some(y) = x {
+LL +         println!("{:?}", y);
+LL ~     };
+   |
+
+error: you seem to be trying to match on a boolean expression
+  --> $DIR/postfix_match.rs:39:5
+   |
+LL | /     test.match {
+LL | |
+LL | |         true => 0,
+LL | |         false => 42,
+LL | |     };
+   | |_____^ help: consider using an `if`/`else` expression: `if test { 0 } else { 42 }`
+   |
+   = note: `-D clippy::match-bool` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::match_bool)]`
+
+error: use `as_ref()` instead
+  --> $DIR/postfix_match.rs:47:33
+   |
+LL |       let borrowed: Option<&()> = owned.match {
+   |  _________________________________^
+LL | |         None => None,
+LL | |         Some(ref v) => Some(v),
+LL | |     };
+   | |_____^ help: try: `owned.as_ref()`
+   |
+   = note: `-D clippy::match-as-ref` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::match_as_ref)]`
+
+error: this match expression is unnecessary
+  --> $DIR/postfix_match.rs:54:19
+   |
+LL |       let _: i32 =  i.match {
+   |  ___________________^
+LL | |         0 => 0,
+LL | |         1 => 1,
+LL | |         2 => 2,
+LL | |         _ => i,
+LL | |     };
+   | |_____^ help: replace it with: `i`
+   |
+   = note: `-D clippy::needless-match` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::needless_match)]`
+
+error: redundant guard
+  --> $DIR/postfix_match.rs:74:20
+   |
+LL |         C(x, y) if 1 == y => ..,
+   |                    ^^^^^^
+   |
+   = note: `-D clippy::redundant-guards` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::redundant_guards)]`
+help: try
+   |
+LL -         C(x, y) if 1 == y => ..,
+LL +         C(x, 1) => ..,
+   |
+
+error: aborting due to 6 previous errors
+