Merge #3407

3407: Fix `possible_missing_comma` false positives r=oli-obk a=mikerite

`possible_missing_comma` should only trigger when the binary operator has
unary equivalent. Otherwise, it's not possible to insert a comma without
breaking compilation. The operators identified were `+`, `&`, `*` and `-`.

This fixes the specific examples given in issues #3244 and #3396
but doesn't address the conflict this lint has with the style of starting
a line with a binary operator.

Co-authored-by: Michael Wright <mikerite@lavabit.com>

clippy_lints/src/formatting.rs

@@ -173,12 +173,19 @@ fn check_else_if(cx: &EarlyContext<'_>, expr: &ast::Expr) {
     }
 }
 
+fn has_unary_equivalent(bin_op: ast::BinOpKind) -> bool {
+    // &, *, -
+    bin_op == ast::BinOpKind::And
+    || bin_op == ast::BinOpKind::Mul
+    || bin_op == ast::BinOpKind::Sub
+}
+
 /// Implementation of the `POSSIBLE_MISSING_COMMA` lint for array
 fn check_array(cx: &EarlyContext<'_>, expr: &ast::Expr) {
     if let ast::ExprKind::Array(ref array) = expr.node {
         for element in array {
             if let ast::ExprKind::Binary(ref op, ref lhs, _) = element.node {
-                if !differing_macro_contexts(lhs.span, op.span) {
+                if has_unary_equivalent(op.node) && !differing_macro_contexts(lhs.span, op.span) {
                     let space_span = lhs.span.between(op.span);
                     if let Some(space_snippet) = snippet_opt(cx, space_span) {
                         let lint_span = lhs.span.with_lo(lhs.span.hi());

tests/ui/formatting.rs

@@ -112,4 +112,16 @@ fn main() {
         1 + 2, 3 +
         4, 5 + 6,
     ];
+
+    // don't lint for bin op without unary equiv
+    // issue 3244
+    vec![
+        1
+        / 2,
+    ];
+    // issue 3396
+    vec![
+        true
+        | false,
+    ];
 }