Keep space if expr follows identifier when lint unused parens

Author: mu001999

compiler/rustc_lint/src/unused.rs

@@ -843,6 +843,10 @@ trait UnusedDelimLint {
                 && !snip.ends_with(' ')
             {
                 " "
+            } else if let Ok(snip) = sm.span_to_prev_source(value_span)
+                && snip.ends_with(|c: char| c.is_alphanumeric())
+            {
+                " "
             } else {
                 ""
             };
@@ -852,6 +856,10 @@ trait UnusedDelimLint {
                 && !snip.starts_with(' ')
             {
                 " "
+            } else if let Ok(snip) = sm.span_to_prev_source(value_span)
+                && snip.starts_with(|c: char| c.is_alphanumeric())
+            {
+                " "
             } else {
                 ""
             };

tests/ui/lint/unused_parens_follow_ident.fixed

@@ -0,0 +1,17 @@
+//@ run-rustfix
+
+#![deny(unused_parens)]
+
+macro_rules! wrap {
+    ($name:ident $arg:expr) => {
+        $name($arg);
+    };
+}
+
+fn main() {
+    wrap!(unary routine()); //~ ERROR unnecessary parentheses around function argument
+    wrap!(unary routine()); //~ ERROR unnecessary parentheses around function argument
+}
+
+fn unary(_: ()) {}
+fn routine() {}

tests/ui/lint/unused_parens_follow_ident.rs

@@ -0,0 +1,17 @@
+//@ run-rustfix
+
+#![deny(unused_parens)]
+
+macro_rules! wrap {
+    ($name:ident $arg:expr) => {
+        $name($arg);
+    };
+}
+
+fn main() {
+    wrap!(unary(routine())); //~ ERROR unnecessary parentheses around function argument
+    wrap!(unary (routine())); //~ ERROR unnecessary parentheses around function argument
+}
+
+fn unary(_: ()) {}
+fn routine() {}

tests/ui/lint/unused_parens_follow_ident.stderr

@@ -0,0 +1,31 @@
+error: unnecessary parentheses around function argument
+  --> $DIR/unused_parens_follow_ident.rs:12:16
+   |
+LL |     wrap!(unary(routine()));
+   |                ^         ^
+   |
+note: the lint level is defined here
+  --> $DIR/unused_parens_follow_ident.rs:3:9
+   |
+LL | #![deny(unused_parens)]
+   |         ^^^^^^^^^^^^^
+help: remove these parentheses
+   |
+LL -     wrap!(unary(routine()));
+LL +     wrap!(unary routine());
+   |
+
+error: unnecessary parentheses around function argument
+  --> $DIR/unused_parens_follow_ident.rs:13:17
+   |
+LL |     wrap!(unary (routine()));
+   |                 ^         ^
+   |
+help: remove these parentheses
+   |
+LL -     wrap!(unary (routine()));
+LL +     wrap!(unary routine());
+   |
+
+error: aborting due to 2 previous errors
+