1 files changed, 79 insertions, 0 deletions
diff --git a/src/tools/clippy/clippy_lints/src/methods/map_unwrap_or.rs b/src/tools/clippy/clippy_lints/src/methods/map_unwrap_or.rs
new file mode 100644
index 000000000..4a8e7ce4d
--- /dev/null
+++ b/src/tools/clippy/clippy_lints/src/methods/map_unwrap_or.rs
@@ -0,0 +1,79 @@
+use clippy_utils::diagnostics::{span_lint, span_lint_and_sugg};
+use clippy_utils::source::snippet;
+use clippy_utils::ty::is_type_diagnostic_item;
+use clippy_utils::usage::mutated_variables;
+use clippy_utils::{meets_msrv, msrvs};
+use rustc_errors::Applicability;
+use rustc_hir as hir;
+use rustc_lint::LateContext;
+use rustc_semver::RustcVersion;
+use rustc_span::symbol::sym;
+
+use super::MAP_UNWRAP_OR;
+
+/// lint use of `map().unwrap_or_else()` for `Option`s and `Result`s
+/// Return true if lint triggered
+pub(super) fn check<'tcx>(
+    cx: &LateContext<'tcx>,
+    expr: &'tcx hir::Expr<'_>,
+    recv: &'tcx hir::Expr<'_>,
+    map_arg: &'tcx hir::Expr<'_>,
+    unwrap_arg: &'tcx hir::Expr<'_>,
+    msrv: Option<RustcVersion>,
+) -> bool {
+    // lint if the caller of `map()` is an `Option`
+    let is_option = is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(recv), sym::Option);
+    let is_result = is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(recv), sym::Result);
+
+    if is_result && !meets_msrv(msrv, msrvs::RESULT_MAP_OR_ELSE) {
+        return false;
+    }
+
+    if is_option || is_result {
+        // Don't make a suggestion that may fail to compile due to mutably borrowing
+        // the same variable twice.
+        let map_mutated_vars = mutated_variables(recv, cx);
+        let unwrap_mutated_vars = mutated_variables(unwrap_arg, cx);
+        if let (Some(map_mutated_vars), Some(unwrap_mutated_vars)) = (map_mutated_vars, unwrap_mutated_vars) {
+            if map_mutated_vars.intersection(&unwrap_mutated_vars).next().is_some() {
+                return false;
+            }
+        } else {
+            return false;
+        }
+
+        // lint message
+        let msg = if is_option {
+            "called `map(<f>).unwrap_or_else(<g>)` on an `Option` value. This can be done more directly by calling \
+            `map_or_else(<g>, <f>)` instead"
+        } else {
+            "called `map(<f>).unwrap_or_else(<g>)` on a `Result` value. This can be done more directly by calling \
+            `.map_or_else(<g>, <f>)` instead"
+        };
+        // get snippets for args to map() and unwrap_or_else()
+        let map_snippet = snippet(cx, map_arg.span, "..");
+        let unwrap_snippet = snippet(cx, unwrap_arg.span, "..");
+        // lint, with note if neither arg is > 1 line and both map() and
+        // unwrap_or_else() have the same span
+        let multiline = map_snippet.lines().count() > 1 || unwrap_snippet.lines().count() > 1;
+        let same_span = map_arg.span.ctxt() == unwrap_arg.span.ctxt();
+        if same_span && !multiline {
+            let var_snippet = snippet(cx, recv.span, "..");
+            span_lint_and_sugg(
+                cx,
+                MAP_UNWRAP_OR,
+                expr.span,
+                msg,
+                "try this",
+                format!("{}.map_or_else({}, {})", var_snippet, unwrap_snippet, map_snippet),
+                Applicability::MachineApplicable,
+            );
+            return true;
+        } else if same_span && multiline {
+            span_lint(cx, MAP_UNWRAP_OR, expr.span, msg);
+            return true;
+        }
+    }
+
+    false
+}