Update upstream source from tag 'upstream/1.52.1+dfsg1'

[rustc.git] / src / tools / clippy / clippy_lints / src / methods / map_collect_result_unit.rs

diff --git a/src/tools/clippy/clippy_lints/src/methods/map_collect_result_unit.rs b/src/tools/clippy/clippy_lints/src/methods/map_collect_result_unit.rs
new file mode 100644 (file)
index 0000000..5b20e26
--- /dev/null
+++ b/src/tools/clippy/clippy_lints/src/methods/map_collect_result_unit.rs
@@ -0,0 +1,45 @@
+use crate::utils::{is_type_diagnostic_item, match_trait_method, paths, snippet, span_lint_and_sugg};
+use if_chain::if_chain;
+use rustc_errors::Applicability;
+use rustc_hir as hir;
+use rustc_lint::LateContext;
+use rustc_middle::ty;
+use rustc_span::symbol::sym;
+
+use super::MAP_COLLECT_RESULT_UNIT;
+
+pub(super) fn check(
+    cx: &LateContext<'_>,
+    expr: &hir::Expr<'_>,
+    map_args: &[hir::Expr<'_>],
+    collect_args: &[hir::Expr<'_>],
+) {
+    if_chain! {
+        // called on Iterator
+        if let [map_expr] = collect_args;
+        if match_trait_method(cx, map_expr, &paths::ITERATOR);
+        // return of collect `Result<(),_>`
+        let collect_ret_ty = cx.typeck_results().expr_ty(expr);
+        if is_type_diagnostic_item(cx, collect_ret_ty, sym::result_type);
+        if let ty::Adt(_, substs) = collect_ret_ty.kind();
+        if let Some(result_t) = substs.types().next();
+        if result_t.is_unit();
+        // get parts for snippet
+        if let [iter, map_fn] = map_args;
+        then {
+            span_lint_and_sugg(
+                cx,
+                MAP_COLLECT_RESULT_UNIT,
+                expr.span,
+                "`.map().collect()` can be replaced with `.try_for_each()`",
+                "try this",
+                format!(
+                    "{}.try_for_each({})",
+                    snippet(cx, iter.span, ".."),
+                    snippet(cx, map_fn.span, "..")
+                ),
+                Applicability::MachineApplicable,
+            );
+        }
+    }
+}