New lint for assignment to temporary

src/temporary_assignment.rs

@@ -0,0 +1,44 @@
+use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
+use rustc_front::hir::{Expr, ExprAssign, ExprField, ExprStruct, ExprTup, ExprTupField};
+
+use utils::is_adjusted;
+use utils::span_lint;
+
+declare_lint! {
+    pub TEMPORARY_ASSIGNMENT,
+    Warn,
+    "assignments to temporaries"
+}
+
+fn is_temporary(expr: &Expr) -> bool {
+    match expr.node {
+        ExprStruct(..) |
+        ExprTup(..) => true,
+        _ => false,
+    }
+}
+
+#[derive(Copy, Clone)]
+pub struct TemporaryAssignmentPass;
+
+impl LintPass for TemporaryAssignmentPass {
+    fn get_lints(&self) -> LintArray {
+        lint_array!(TEMPORARY_ASSIGNMENT)
+    }
+}
+
+impl LateLintPass for TemporaryAssignmentPass {
+    fn check_expr(&mut self, cx: &LateContext, expr: &Expr) {
+        if let ExprAssign(ref target, _) = expr.node {
+            match target.node {
+                ExprField(ref base, _) | ExprTupField(ref base, _) => {
+                    if is_temporary(base) && !is_adjusted(cx, base) {
+                        span_lint(cx, TEMPORARY_ASSIGNMENT, expr.span,
+                                  "assignment to temporary");
+                    }
+                }
+                _ => ()
+            }
+        }
+    }
+}