New lint for assignment to temporary

src/lib.rs

@@ -54,6 +54,7 @@ pub mod open_options;
 pub mod needless_features;
 pub mod needless_update;
 pub mod no_effect;
+pub mod temporary_assignment;
 
 mod reexport {
     pub use syntax::ast::{Name, Ident, NodeId};
@@ -102,6 +103,7 @@ pub fn plugin_registrar(reg: &mut Registry) {
     reg.register_late_lint_pass(box needless_update::NeedlessUpdatePass);
     reg.register_late_lint_pass(box no_effect::NoEffectPass);
     reg.register_late_lint_pass(box map_clone::MapClonePass);
+    reg.register_late_lint_pass(box temporary_assignment::TemporaryAssignmentPass);
 
     reg.register_lint_group("clippy_pedantic", vec![
         methods::OPTION_UNWRAP_USED,
@@ -172,6 +174,7 @@ pub fn plugin_registrar(reg: &mut Registry) {
         ranges::RANGE_ZIP_WITH_LEN,
         returns::LET_AND_RETURN,
         returns::NEEDLESS_RETURN,
+        temporary_assignment::TEMPORARY_ASSIGNMENT,
         types::BOX_VEC,
         types::LET_UNIT_VALUE,
         types::LINKEDLIST,

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");
+                    }
+                }
+                _ => ()
+            }
+        }
+    }
+}