Implement support for implicit start and end

Author: DennisOSRM

clippy_lints/src/needless_parens_on_range_literal.rs

@@ -75,15 +75,13 @@ fn check_for_parens(cx: &LateContext<'_>, e: &Expr<'_>, is_start: bool) {
 
 impl<'tcx> LateLintPass<'tcx> for NeedlessParensOnRangeLiteral {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
-        // if let higher::Range { start, end, limits } = &e.kind {
-        if let Some(higher::Range {
-            start: Some(start),
-            end: Some(end),
-            ..
-        }) = higher::Range::hir(expr)
-        {
-            check_for_parens(cx, start, true);
-            check_for_parens(cx, end, false);
+        if let Some(higher::Range { start, end, .. }) = higher::Range::hir(expr) {
+            if let Some(start) = start {
+                check_for_parens(cx, start, true);
+            }
+            if let Some(end) = end {
+                check_for_parens(cx, end, false);
+            }
         }
     }
 }

tests/ui/needless_parens_on_range_literal.fixed

@@ -6,7 +6,9 @@
 
 fn main() {
     let _ = 'a'..='z';
-    let _ = 'a'..='z';
+    let _ = 'a'..'z';
     let _ = (1.)..2.;
     let _ = (1.)..2.;
+    let _ = 'a'..;
+    let _ = ..'z';
 }

tests/ui/needless_parens_on_range_literal.rs

@@ -6,7 +6,9 @@
 
 fn main() {
     let _ = ('a')..=('z');
-    let _ = 'a'..='z';
+    let _ = 'a'..('z');
     let _ = (1.)..2.;
     let _ = (1.)..(2.);
+    let _ = ('a')..;
+    let _ = ..('z');
 }

tests/ui/needless_parens_on_range_literal.stderr

@@ -12,11 +12,29 @@ error: needless parenthesis on range literal can be removed
 LL |     let _ = ('a')..=('z');
    |                     ^^^^^ help: try: `'z'`
 
+error: needless parenthesis on range literal can be removed
+  --> $DIR/needless_parens_on_range_literal.rs:9:18
+   |
+LL |     let _ = 'a'..('z');
+   |                  ^^^^^ help: try: `'z'`
+
 error: needless parenthesis on range literal can be removed
   --> $DIR/needless_parens_on_range_literal.rs:11:19
    |
 LL |     let _ = (1.)..(2.);
    |                   ^^^^ help: try: `2.`
 
-error: aborting due to 3 previous errors
+error: needless parenthesis on range literal can be removed
+  --> $DIR/needless_parens_on_range_literal.rs:12:13
+   |
+LL |     let _ = ('a')..;
+   |             ^^^^^ help: try: `'a'`
+
+error: needless parenthesis on range literal can be removed
+  --> $DIR/needless_parens_on_range_literal.rs:13:15
+   |
+LL |     let _ = ..('z');
+   |               ^^^^^ help: try: `'z'`
+
+error: aborting due to 6 previous errors