From 35d6a2ef2ba71d5ea120c2879825968babcf9a89 Mon Sep 17 00:00:00 2001
From: Lukas Wirth <lukastw97@gmail.com>
Date: Sun, 2 Aug 2020 16:30:09 +0200
Subject: [PATCH] Lint path statements to use drop for drop types
---
src/librustc_lint/unused.rs | 20 ++++++++++++++++++--
src/test/ui/warn-path-statement.rs | 13 ++++++++++++-
src/test/ui/warn-path-statement.stderr | 16 ++++++++++++++--
3 files changed, 44 insertions(+), 5 deletions(-)
diff --git a/src/librustc_lint/unused.rs b/src/librustc_lint/unused.rs
index 8d8fb8c3c6098..ee4361ce16b62 100644
--- a/src/librustc_lint/unused.rs
+++ b/src/librustc_lint/unused.rs
@@ -275,10 +275,26 @@ declare_lint_pass!(PathStatements => [PATH_STATEMENTS]);
impl<'tcx> LateLintPass<'tcx> for PathStatements {
fn check_stmt(&mut self, cx: &LateContext<'_>, s: &hir::Stmt<'_>) {
- if let hir::StmtKind::Semi(ref expr) = s.kind {
+ if let hir::StmtKind::Semi(expr) = s.kind {
if let hir::ExprKind::Path(_) = expr.kind {
cx.struct_span_lint(PATH_STATEMENTS, s.span, |lint| {
- lint.build("path statement with no effect").emit()
+ let ty = cx.typeck_results().expr_ty(expr);
+ if ty.needs_drop(cx.tcx, cx.param_env) {
+ let mut lint = lint.build("path statement drops value");
+ if let Ok(snippet) = cx.sess().source_map().span_to_snippet(expr.span) {
+ lint.span_suggestion(
+ s.span,
+ "use `drop` to clarify the intent",
+ format!("drop({});", snippet),
+ Applicability::MachineApplicable,
+ );
+ } else {
+ lint.span_help(s.span, "use `drop` to clarify the intent");
+ }
+ lint.emit()
+ } else {
+ lint.build("path statement with no effect").emit()
+ }
});
}
}
diff --git a/src/test/ui/warn-path-statement.rs b/src/test/ui/warn-path-statement.rs
index e8525f8b892d6..2435be623f310 100644
--- a/src/test/ui/warn-path-statement.rs
+++ b/src/test/ui/warn-path-statement.rs
@@ -1,6 +1,17 @@
// compile-flags: -D path-statements
-fn main() {
+struct Droppy;
+
+impl Drop for Droppy {
+ fn drop(&mut self) {}
+}
+fn main() {
let x = 10;
x; //~ ERROR path statement with no effect
+
+ let y = Droppy;
+ y; //~ ERROR path statement drops value
+
+ let z = (Droppy,);
+ z; //~ ERROR path statement drops value
}
diff --git a/src/test/ui/warn-path-statement.stderr b/src/test/ui/warn-path-statement.stderr
index 30afb99e5f02c..248d2ef299be3 100644
--- a/src/test/ui/warn-path-statement.stderr
+++ b/src/test/ui/warn-path-statement.stderr
@@ -1,10 +1,22 @@
error: path statement with no effect
- --> $DIR/warn-path-statement.rs:5:5
+ --> $DIR/warn-path-statement.rs:10:5
|
LL | x;
| ^^
|
= note: requested on the command line with `-D path-statements`
-error: aborting due to previous error
+error: path statement drops value
+ --> $DIR/warn-path-statement.rs:13:5
+ |
+LL | y;
+ | ^^ help: use `drop` to clarify the intent: `drop(y);`
+
+error: path statement drops value
+ --> $DIR/warn-path-statement.rs:16:5
+ |
+LL | z;
+ | ^^ help: use `drop` to clarify the intent: `drop(z);`
+
+error: aborting due to 3 previous errors