From ea733172e69844d772b4c9e80daf2745ac3355b1 Mon Sep 17 00:00:00 2001
From: Guillaume Gomez <guillaume1.gomez@gmail.com>
Date: Fri, 24 Nov 2023 17:56:47 +0100
Subject: [PATCH] Create new lint `option_map_or_err_ok`

---
 clippy_lints/src/declared_lints.rs            |  1 +
 clippy_lints/src/methods/mod.rs               | 28 +++++++++++++
 .../src/methods/option_map_or_err_ok.rs       | 41 +++++++++++++++++++
 3 files changed, 70 insertions(+)
 create mode 100644 clippy_lints/src/methods/option_map_or_err_ok.rs

diff --git a/clippy_lints/src/declared_lints.rs b/clippy_lints/src/declared_lints.rs
index 7d4ab9fde1f..5a109fcc2cc 100644
--- a/clippy_lints/src/declared_lints.rs
+++ b/clippy_lints/src/declared_lints.rs
@@ -405,6 +405,7 @@
     crate::methods::OK_EXPECT_INFO,
     crate::methods::OPTION_AS_REF_DEREF_INFO,
     crate::methods::OPTION_FILTER_MAP_INFO,
+    crate::methods::OPTION_MAP_OR_ERR_OK_INFO,
     crate::methods::OPTION_MAP_OR_NONE_INFO,
     crate::methods::OR_FUN_CALL_INFO,
     crate::methods::OR_THEN_UNWRAP_INFO,
diff --git a/clippy_lints/src/methods/mod.rs b/clippy_lints/src/methods/mod.rs
index 71de77acfc1..7ce14242cae 100644
--- a/clippy_lints/src/methods/mod.rs
+++ b/clippy_lints/src/methods/mod.rs
@@ -70,6 +70,7 @@
 mod ok_expect;
 mod open_options;
 mod option_as_ref_deref;
+mod option_map_or_err_ok;
 mod option_map_or_none;
 mod option_map_unwrap_or;
 mod or_fun_call;
@@ -3726,6 +3727,31 @@
     "calls to `Path::join` which will overwrite the original path"
 }
 
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for usage of `_.map_or(Err(_), Ok)`.
+    ///
+    /// ### Why is this bad?
+    /// Readability, this can be written more concisely as
+    /// `_.ok_or(_)`.
+    ///
+    /// ### Example
+    /// ```no_run
+    /// # let opt = Some(1);
+    /// opt.map_or(Err("error"), Ok);
+    /// ```
+    ///
+    /// Use instead:
+    /// ```no_run
+    /// # let opt = Some(1);
+    /// opt.ok_or("error");
+    /// ```
+    #[clippy::version = "1.76.0"]
+    pub OPTION_MAP_OR_ERR_OK,
+    style,
+    "using `Option.map_or(Err(_), Ok)`, which is more succinctly expressed as `Option.ok_or(_)`"
+}
+
 pub struct Methods {
     avoid_breaking_exported_api: bool,
     msrv: Msrv,
@@ -3876,6 +3902,7 @@ pub fn new(
     WAKER_CLONE_WAKE,
     UNNECESSARY_FALLIBLE_CONVERSIONS,
     JOIN_ABSOLUTE_PATHS,
+    OPTION_MAP_OR_ERR_OK,
 ]);
 
 /// Extracts a method call name, args, and `Span` of the method name.
@@ -4335,6 +4362,7 @@ fn check_methods<'tcx>(&self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
                 ("map_or", [def, map]) => {
                     option_map_or_none::check(cx, expr, recv, def, map);
                     manual_ok_or::check(cx, expr, recv, def, map);
+                    option_map_or_err_ok::check(cx, expr, recv, def, map);
                 },
                 ("map_or_else", [def, map]) => {
                     result_map_or_else_none::check(cx, expr, recv, def, map);
diff --git a/clippy_lints/src/methods/option_map_or_err_ok.rs b/clippy_lints/src/methods/option_map_or_err_ok.rs
new file mode 100644
index 00000000000..91e39d5a1cd
--- /dev/null
+++ b/clippy_lints/src/methods/option_map_or_err_ok.rs
@@ -0,0 +1,41 @@
+use clippy_utils::diagnostics::span_lint_and_sugg;
+use clippy_utils::source::snippet;
+use clippy_utils::ty::is_type_diagnostic_item;
+use clippy_utils::{is_res_lang_ctor, path_res};
+use rustc_errors::Applicability;
+use rustc_hir::LangItem::{ResultErr, ResultOk};
+use rustc_hir::{Expr, ExprKind};
+use rustc_lint::LateContext;
+use rustc_span::symbol::sym;
+
+use super::OPTION_MAP_OR_ERR_OK;
+
+pub(super) fn check<'tcx>(
+    cx: &LateContext<'tcx>,
+    expr: &'tcx Expr<'tcx>,
+    recv: &'tcx Expr<'_>,
+    or_expr: &'tcx Expr<'_>,
+    map_expr: &'tcx Expr<'_>,
+) {
+    // We check that it's called on an `Option` type.
+    if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(recv), sym::Option)
+        // We check that first we pass an `Err`.
+        && let ExprKind::Call(call, &[arg]) = or_expr.kind
+        && is_res_lang_ctor(cx, path_res(cx, call), ResultErr)
+        // And finally we check that it is mapped as `Ok`.
+        && is_res_lang_ctor(cx, path_res(cx, map_expr), ResultOk)
+    {
+        let msg = "called `map_or(Err(_), Ok)` on an `Option` value";
+        let self_snippet = snippet(cx, recv.span, "..");
+        let err_snippet = snippet(cx, arg.span, "..");
+        span_lint_and_sugg(
+            cx,
+            OPTION_MAP_OR_ERR_OK,
+            expr.span,
+            msg,
+            "try using `ok_or` instead",
+            format!("{self_snippet}.ok_or({err_snippet})"),
+            Applicability::MachineApplicable,
+        );
+    }
+}