From cd0a3c4bcf3ec6e2ff4f7f3c96532cca50ea26a1 Mon Sep 17 00:00:00 2001
From: Yukang <moorekang@gmail.com>
Date: Tue, 30 Jun 2026 08:17:50 +0800
Subject: [PATCH] Fix spacing issue for unused parentheses lint

---
 compiler/rustc_lint/src/unused.rs             |  2 +-
 ...used-parens-trailing-space-issue-158583.rs |  5 +++++
 ...-parens-trailing-space-issue-158583.stderr | 19 +++++++++++++++++++
 3 files changed, 25 insertions(+), 1 deletion(-)
 create mode 100644 tests/ui/lint/unused-parens-trailing-space-issue-158583.rs
 create mode 100644 tests/ui/lint/unused-parens-trailing-space-issue-158583.stderr

diff --git a/compiler/rustc_lint/src/unused.rs b/compiler/rustc_lint/src/unused.rs
index dd2cb505cb1bc..5d1b82b0bb48c 100644
--- a/compiler/rustc_lint/src/unused.rs
+++ b/compiler/rustc_lint/src/unused.rs
@@ -338,7 +338,7 @@ trait UnusedDelimLint {
                 && !snip.starts_with(' ')
             {
                 " "
-            } else if let Ok(snip) = sm.span_to_prev_source(value_span)
+            } else if let Ok(snip) = sm.span_to_next_source(value_span)
                 && snip.starts_with(|c: char| c.is_alphanumeric())
             {
                 " "
diff --git a/tests/ui/lint/unused-parens-trailing-space-issue-158583.rs b/tests/ui/lint/unused-parens-trailing-space-issue-158583.rs
new file mode 100644
index 0000000000000..d3c70f8769a9c
--- /dev/null
+++ b/tests/ui/lint/unused-parens-trailing-space-issue-158583.rs
@@ -0,0 +1,5 @@
+fn main() {
+    #[deny(unused_parens)]
+    let _x = (3 + 6);
+    //~^ ERROR unnecessary parentheses around assigned value
+}
diff --git a/tests/ui/lint/unused-parens-trailing-space-issue-158583.stderr b/tests/ui/lint/unused-parens-trailing-space-issue-158583.stderr
new file mode 100644
index 0000000000000..200379a5151eb
--- /dev/null
+++ b/tests/ui/lint/unused-parens-trailing-space-issue-158583.stderr
@@ -0,0 +1,19 @@
+error: unnecessary parentheses around assigned value
+  --> $DIR/unused-parens-trailing-space-issue-158583.rs:3:14
+   |
+LL |     let _x = (3 + 6);
+   |              ^     ^
+   |
+note: the lint level is defined here
+  --> $DIR/unused-parens-trailing-space-issue-158583.rs:2:12
+   |
+LL |     #[deny(unused_parens)]
+   |            ^^^^^^^^^^^^^
+help: remove these parentheses
+   |
+LL -     let _x = (3 + 6);
+LL +     let _x = 3 + 6;
+   |
+
+error: aborting due to 1 previous error
+