allow check for `match` in lint [`option_if_let_else`]

and add test case for `Result`

4 files changed, 183 insertions, 45 deletions

diff --git a/clippy_lints/src/option_if_let_else.rs b/clippy_lints/src/option_if_let_else.rs
index 44f153cffac..b99966c5a5d 100644
--- a/clippy_lints/src/option_if_let_else.rs
+++ b/clippy_lints/src/option_if_let_else.rs
@@ -7,15 +7,18 @@ use clippy_utils::{
 };
 use if_chain::if_chain;
 use rustc_errors::Applicability;
-use rustc_hir::LangItem::OptionSome;
-use rustc_hir::{def::Res, BindingAnnotation, Expr, ExprKind, Mutability, PatKind, Path, QPath, UnOp};
+use rustc_hir::LangItem::{OptionNone, OptionSome};
+use rustc_hir::{
+    def::Res, Arm, BindingAnnotation, Expr, ExprKind, MatchSource, Mutability, Pat, PatKind, Path, QPath, UnOp,
+};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_session::{declare_lint_pass, declare_tool_lint};
 use rustc_span::sym;
 
 declare_clippy_lint! {
     /// ### What it does
-    /// Lints usage of `if let Some(v) = ... { y } else { x }` which is more
+    /// Lints usage of `if let Some(v) = ... { y } else { x }` and
+    /// `match .. { Some(v) => y, None/_ => x }` which are more
     /// idiomatically done with `Option::map_or` (if the else bit is a pure
     /// expression) or `Option::map_or_else` (if the else bit is an impure
     /// expression).
@@ -39,6 +42,10 @@ declare_clippy_lint! {
     /// } else {
     ///     5
     /// };
+    /// let _ = match optional {
+    ///     Some(val) => val + 1,
+    ///     None => 5
+    /// };
     /// let _ = if let Some(foo) = optional {
     ///     foo
     /// } else {
@@ -53,6 +60,7 @@ declare_clippy_lint! {
     /// # let optional: Option<u32> = Some(0);
     /// # fn do_complicated_function() -> u32 { 5 };
     /// let _ = optional.map_or(5, |foo| foo);
+    /// let _ = optional.map_or(5, |val| val + 1);
     /// let _ = optional.map_or_else(||{
     ///     let y = do_complicated_function();
     ///     y*y
@@ -76,9 +84,21 @@ fn is_result_ok(cx: &LateContext<'_>, expr: &'_ Expr<'_>) -> bool {
     }
 }
 
-/// A struct containing information about occurrences of the
-/// `if let Some(..) = .. else` construct that this lint detects.
-struct OptionIfLetElseOccurrence {
+/// A struct containing information about occurrences of construct that this lint detects
+///
+/// Such as:
+///
+/// ```ignore
+/// if let Some(..) = {..} else {..}
+/// ```
+/// or
+/// ```ignore
+/// match x {
+///     Some(..) => {..},
+///     None/_ => {..}
+/// }
+/// ```
+struct OptionOccurence {
     option: String,
     method_sugg: String,
     some_expr: String,
@@ -99,43 +119,39 @@ fn format_option_in_sugg(cx: &LateContext<'_>, cond_expr: &Expr<'_>, as_ref: boo
     )
 }
 
-/// If this expression is the option if let/else construct we're detecting, then
-/// this function returns an `OptionIfLetElseOccurrence` struct with details if
-/// this construct is found, or None if this construct is not found.
-fn detect_option_if_let_else<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'tcx>) -> Option<OptionIfLetElseOccurrence> {
+fn try_get_option_occurence<'tcx>(
+    cx: &LateContext<'tcx>,
+    pat: &Pat<'tcx>,
+    expr: &Expr<'_>,
+    if_then: &'tcx Expr<'_>,
+    if_else: &'tcx Expr<'_>,
+) -> Option<OptionOccurence> {
+    let cond_expr = match expr.kind {
+        ExprKind::Unary(UnOp::Deref, inner_expr) | ExprKind::AddrOf(_, _, inner_expr) => inner_expr,
+        _ => expr,
+    };
     if_chain! {
-        if !expr.span.from_expansion(); // Don't lint macros, because it behaves weirdly
-        if !in_constant(cx, expr.hir_id);
-        if let Some(higher::IfLet { let_pat, let_expr, if_then, if_else: Some(if_else) })
-            = higher::IfLet::hir(cx, expr);
-        if !is_else_clause(cx.tcx, expr);
-        if !is_result_ok(cx, let_expr); // Don't lint on Result::ok because a different lint does it already
-        if let PatKind::TupleStruct(struct_qpath, [inner_pat], _) = &let_pat.kind;
-        if is_lang_ctor(cx, struct_qpath, OptionSome);
-        if let PatKind::Binding(bind_annotation, _, id, None) = &inner_pat.kind;
+        if !is_result_ok(cx, cond_expr); // Don't lint on Result::ok because a different lint does it already
+        let inner_pat = try_get_inner_pat(cx, pat)?;
+        if let PatKind::Binding(bind_annotation, _, id, None) = inner_pat.kind;
         if let Some(some_captures) = can_move_expr_to_closure(cx, if_then);
         if let Some(none_captures) = can_move_expr_to_closure(cx, if_else);
         if some_captures
             .iter()
             .filter_map(|(id, &c)| none_captures.get(id).map(|&c2| (c, c2)))
             .all(|(x, y)| x.is_imm_ref() && y.is_imm_ref());
-
         then {
-            let capture_mut = if bind_annotation == &BindingAnnotation::Mutable { "mut " } else { "" };
+            let capture_mut = if bind_annotation == BindingAnnotation::Mutable { "mut " } else { "" };
             let some_body = peel_blocks(if_then);
             let none_body = peel_blocks(if_else);
             let method_sugg = if eager_or_lazy::switch_to_eager_eval(cx, none_body) { "map_or" } else { "map_or_else" };
             let capture_name = id.name.to_ident_string();
-            let (as_ref, as_mut) = match &let_expr.kind {
+            let (as_ref, as_mut) = match &expr.kind {
                 ExprKind::AddrOf(_, Mutability::Not, _) => (true, false),
                 ExprKind::AddrOf(_, Mutability::Mut, _) => (false, true),
-                _ => (bind_annotation == &BindingAnnotation::Ref, bind_annotation == &BindingAnnotation::RefMut),
-            };
-            let cond_expr = match let_expr.kind {
-                // Pointer dereferencing happens automatically, so we can omit it in the suggestion
-                ExprKind::Unary(UnOp::Deref, expr) | ExprKind::AddrOf(_, _, expr) => expr,
-                _ => let_expr,
+                _ => (bind_annotation == BindingAnnotation::Ref, bind_annotation == BindingAnnotation::RefMut),
             };
+
             // Check if captures the closure will need conflict with borrows made in the scrutinee.
             // TODO: check all the references made in the scrutinee expression. This will require interacting
             // with the borrow checker. Currently only `<local>[.<field>]*` is checked for.
@@ -154,33 +170,99 @@ fn detect_option_if_let_else<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'tcx>) ->
                     }
                 }
             }
-            Some(OptionIfLetElseOccurrence {
+
+            return Some(OptionOccurence {
                 option: format_option_in_sugg(cx, cond_expr, as_ref, as_mut),
                 method_sugg: method_sugg.to_string(),
                 some_expr: format!("|{}{}| {}", capture_mut, capture_name, Sugg::hir_with_macro_callsite(cx, some_body, "..")),
                 none_expr: format!("{}{}", if method_sugg == "map_or" { "" } else { "|| " }, Sugg::hir_with_macro_callsite(cx, none_body, "..")),
-            })
+            });
+        }
+    }
+
+    None
+}
+
+fn try_get_inner_pat<'tcx>(cx: &LateContext<'tcx>, pat: &Pat<'tcx>) -> Option<&'tcx Pat<'tcx>> {
+    if let PatKind::TupleStruct(ref qpath, [inner_pat], ..) = pat.kind {
+        if is_lang_ctor(cx, qpath, OptionSome) {
+            return Some(inner_pat);
+        }
+    }
+    None
+}
+
+/// If this expression is the option if let/else construct we're detecting, then
+/// this function returns an `OptionOccurence` struct with details if
+/// this construct is found, or None if this construct is not found.
+fn detect_option_if_let_else<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'tcx>) -> Option<OptionOccurence> {
+    if let Some(higher::IfLet {
+        let_pat,
+        let_expr,
+        if_then,
+        if_else: Some(if_else),
+    }) = higher::IfLet::hir(cx, expr)
+    {
+        if !is_else_clause(cx.tcx, expr) {
+            return try_get_option_occurence(cx, let_pat, let_expr, if_then, if_else);
+        }
+    }
+    None
+}
+
+fn detect_option_match<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'tcx>) -> Option<OptionOccurence> {
+    if let ExprKind::Match(ex, arms, MatchSource::Normal) = expr.kind {
+        if let Some((let_pat, if_then, if_else)) = try_convert_match(cx, arms) {
+            return try_get_option_occurence(cx, let_pat, ex, if_then, if_else);
+        }
+    }
+    None
+}
+
+fn try_convert_match<'tcx>(
+    cx: &LateContext<'tcx>,
+    arms: &[Arm<'tcx>],
+) -> Option<(&'tcx Pat<'tcx>, &'tcx Expr<'tcx>, &'tcx Expr<'tcx>)> {
+    if arms.len() == 2 {
+        return if is_none_arm(cx, &arms[1]) {
+            Some((arms[0].pat, arms[0].body, arms[1].body))
+        } else if is_none_arm(cx, &arms[0]) {
+            Some((arms[1].pat, arms[1].body, arms[0].body))
         } else {
             None
-        }
+        };
+    }
+    None
+}
+
+fn is_none_arm(cx: &LateContext<'_>, arm: &Arm<'_>) -> bool {
+    match arm.pat.kind {
+        PatKind::Path(ref qpath) => is_lang_ctor(cx, qpath, OptionNone),
+        PatKind::Wild => true,
+        _ => false,
     }
 }
 
 impl<'tcx> LateLintPass<'tcx> for OptionIfLetElse {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &Expr<'tcx>) {
-        if let Some(detection) = detect_option_if_let_else(cx, expr) {
-            span_lint_and_sugg(
-                cx,
-                OPTION_IF_LET_ELSE,
-                expr.span,
-                format!("use Option::{} instead of an if let/else", detection.method_sugg).as_str(),
-                "try",
-                format!(
-                    "{}.{}({}, {})",
-                    detection.option, detection.method_sugg, detection.none_expr, detection.some_expr,
-                ),
-                Applicability::MaybeIncorrect,
-            );
+        // Don't lint macros, because it behaves weirdly
+        // and don't lint constant as well
+        if !expr.span.from_expansion() && !in_constant(cx, expr.hir_id) {
+            let detection = detect_option_if_let_else(cx, expr).or_else(|| detect_option_match(cx, expr));
+            if let Some(det) = detection {
+                span_lint_and_sugg(
+                    cx,
+                    OPTION_IF_LET_ELSE,
+                    expr.span,
+                    format!("use Option::{} instead of an if let/else", det.method_sugg).as_str(),
+                    "try",
+                    format!(
+                        "{}.{}({}, {})",
+                        det.option, det.method_sugg, det.none_expr, det.some_expr
+                    ),
+                    Applicability::MaybeIncorrect,
+                );
+            }
         }
     }
 }
diff --git a/tests/ui/option_if_let_else.fixed b/tests/ui/option_if_let_else.fixed
index b6d5e106f05..79610a0ea34 100644
--- a/tests/ui/option_if_let_else.fixed
+++ b/tests/ui/option_if_let_else.fixed
@@ -179,4 +179,19 @@ fn main() {
 
     let _ = pattern_to_vec("hello world");
     let _ = complex_subpat();
+
+    // issue #8492
+    let _ = s.map_or(1, |string| string.len());
+    let _ = Some(10).map_or(5, |a| a + 1);
+
+    let res: Result<i32, i32> = Ok(5);
+    let _ = match res {
+        Ok(a) => a + 1,
+        _ => 1,
+    };
+    let _ = match res {
+        Err(_) => 1,
+        Ok(a) => a + 1,
+    };
+    let _ = if let Ok(a) = res { a + 1 } else { 5 };
 }
diff --git a/tests/ui/option_if_let_else.rs b/tests/ui/option_if_let_else.rs
index 35bae159343..9eeaea12d3b 100644
--- a/tests/ui/option_if_let_else.rs
+++ b/tests/ui/option_if_let_else.rs
@@ -208,4 +208,25 @@ fn main() {
 
     let _ = pattern_to_vec("hello world");
     let _ = complex_subpat();
+
+    // issue #8492
+    let _ = match s {
+        Some(string) => string.len(),
+        None => 1,
+    };
+    let _ = match Some(10) {
+        Some(a) => a + 1,
+        None => 5,
+    };
+
+    let res: Result<i32, i32> = Ok(5);
+    let _ = match res {
+        Ok(a) => a + 1,
+        _ => 1,
+    };
+    let _ = match res {
+        Err(_) => 1,
+        Ok(a) => a + 1,
+    };
+    let _ = if let Ok(a) = res { a + 1 } else { 5 };
 }
diff --git a/tests/ui/option_if_let_else.stderr b/tests/ui/option_if_let_else.stderr
index daba606004e..4086b45b7c0 100644
--- a/tests/ui/option_if_let_else.stderr
+++ b/tests/ui/option_if_let_else.stderr
@@ -206,5 +206,25 @@ LL +         s.len() + x
 LL ~     });
    |
 
-error: aborting due to 15 previous errors
+error: use Option::map_or instead of an if let/else
+  --> $DIR/option_if_let_else.rs:212:13
+   |
+LL |       let _ = match s {
+   |  _____________^
+LL | |         Some(string) => string.len(),
+LL | |         None => 1,
+LL | |     };
+   | |_____^ help: try: `s.map_or(1, |string| string.len())`
+
+error: use Option::map_or instead of an if let/else
+  --> $DIR/option_if_let_else.rs:216:13
+   |
+LL |       let _ = match Some(10) {
+   |  _____________^
+LL | |         Some(a) => a + 1,
+LL | |         None => 5,
+LL | |     };
+   | |_____^ help: try: `Some(10).map_or(5, |a| a + 1)`
+
+error: aborting due to 17 previous errors