Merge #10440

10440: Fix Clippy warnings and replace some `if let`s with `match` r=Veykril a=arzg

I decided to try fixing a bunch of Clippy warnings. I am aware of this project’s opinion of Clippy (I have read both [rust-lang/clippy#5537](https://github.com/rust-lang/rust-clippy/issues/5537) and [rust-analyzer/rowan#57 (comment)](https://github.com/rust-analyzer/rowan/pull/57#discussion_r415676159)), so I totally understand if part of or the entirety of this PR is rejected. In particular, I can see how the semicolons and `if let` vs `match` commits provide comparatively little benefit when compared to the ensuing churn.

I tried to separate each kind of change into its own commit to make it easier to discard certain changes. I also only applied Clippy suggestions where I thought they provided a definite improvement to the code (apart from semicolons, which is IMO more of a formatting/consistency question than a linting question). In the end I accumulated a list of 28 Clippy lints I ignored entirely.

Sidenote: I should really have asked about this on Zulip before going through all 1,555 `if let`s in the codebase to decide which ones definitely look better as `match` :P

Co-authored-by: Aramis Razzaghipour <aramisnoah@gmail.com>

crates/hir_ty/src/autoderef.rs

@@ -109,10 +109,9 @@ pub(crate) fn deref(
     ty: InEnvironment<&Canonical<Ty>>,
 ) -> Option<Canonical<Ty>> {
     let _p = profile::span("deref");
-    if let Some(derefed) = builtin_deref(&ty.goal.value) {
-        Some(Canonical { value: derefed, binders: ty.goal.binders.clone() })
-    } else {
-        deref_by_trait(db, krate, ty)
+    match builtin_deref(&ty.goal.value) {
+        Some(derefed) => Some(Canonical { value: derefed, binders: ty.goal.binders.clone() }),
+        None => deref_by_trait(db, krate, ty),
     }
 }
 

crates/hir_ty/src/chalk_ext.rs

@@ -104,10 +104,9 @@ impl TyExt for Ty {
     }
 
     fn as_fn_def(&self, db: &dyn HirDatabase) -> Option<FunctionId> {
-        if let Some(CallableDefId::FunctionId(func)) = self.callable_def(db) {
-            Some(func)
-        } else {
-            None
+        match self.callable_def(db) {
+            Some(CallableDefId::FunctionId(func)) => Some(func),
+            Some(CallableDefId::StructId(_) | CallableDefId::EnumVariantId(_)) | None => None,
         }
     }
     fn as_reference(&self) -> Option<(&Ty, Lifetime, Mutability)> {

crates/hir_ty/src/diagnostics/match_check/deconstruct_pat.rs

@@ -105,10 +105,9 @@ impl IntRange {
 
     #[inline]
     fn from_range(lo: u128, hi: u128, scalar_ty: Scalar) -> IntRange {
-        if let Scalar::Bool = scalar_ty {
-            IntRange { range: lo..=hi }
-        } else {
-            unimplemented!()
+        match scalar_ty {
+            Scalar::Bool => IntRange { range: lo..=hi },
+            _ => unimplemented!(),
         }
     }
 

crates/hir_ty/src/display.rs

@@ -167,10 +167,9 @@ impl<'a> HirFormatter<'a> {
     }
 
     pub fn should_truncate(&self) -> bool {
-        if let Some(max_size) = self.max_size {
-            self.curr_size >= max_size
-        } else {
-            false
+        match self.max_size {
+            Some(max_size) => self.curr_size >= max_size,
+            None => false,
         }
     }
 

crates/hir_ty/src/infer/expr.rs

@@ -264,10 +264,9 @@ impl<'a> InferenceContext<'a> {
 
                 // collect explicitly written argument types
                 for arg_type in arg_types.iter() {
-                    let arg_ty = if let Some(type_ref) = arg_type {
-                        self.make_ty(type_ref)
-                    } else {
-                        self.table.new_type_var()
+                    let arg_ty = match arg_type {
+                        Some(type_ref) => self.make_ty(type_ref),
+                        None => self.table.new_type_var(),
                     };
                     sig_tys.push(arg_ty);
                 }

crates/hir_ty/src/infer/pat.rs

@@ -204,10 +204,9 @@ impl<'a> InferenceContext<'a> {
                 } else {
                     BindingMode::convert(*mode)
                 };
-                let inner_ty = if let Some(subpat) = subpat {
-                    self.infer_pat(*subpat, &expected, default_bm)
-                } else {
-                    expected
+                let inner_ty = match subpat {
+                    Some(subpat) => self.infer_pat(*subpat, &expected, default_bm),
+                    None => expected,
                 };
                 let inner_ty = self.insert_type_vars_shallow(inner_ty);
 

crates/hir_ty/src/infer/unify.rs

@@ -324,10 +324,9 @@ impl<'a> InferenceTable<'a> {
 
     /// Unify two types and register new trait goals that arise from that.
     pub(crate) fn unify(&mut self, ty1: &Ty, ty2: &Ty) -> bool {
-        let result = if let Ok(r) = self.try_unify(ty1, ty2) {
-            r
-        } else {
-            return false;
+        let result = match self.try_unify(ty1, ty2) {
+            Ok(r) => r,
+            Err(_) => return false,
         };
         self.register_infer_ok(result);
         true

crates/hir_ty/src/lower.rs

@@ -369,10 +369,9 @@ impl<'a> TyLoweringContext<'a> {
                 Some((it, None)) => it,
                 _ => return None,
             };
-        if let TypeNs::GenericParam(param_id) = resolution {
-            Some(param_id)
-        } else {
-            None
+        match resolution {
+            TypeNs::GenericParam(param_id) => Some(param_id),
+            _ => None,
         }
     }
 

crates/hir_ty/src/method_resolution.rs

@@ -82,10 +82,9 @@ impl TyFingerprint {
             TyKind::Ref(_, _, ty) => return TyFingerprint::for_trait_impl(ty),
             TyKind::Tuple(_, subst) => {
                 let first_ty = subst.interned().get(0).map(|arg| arg.assert_ty_ref(&Interner));
-                if let Some(ty) = first_ty {
-                    return TyFingerprint::for_trait_impl(ty);
-                } else {
-                    TyFingerprint::Unit
+                match first_ty {
+                    Some(ty) => return TyFingerprint::for_trait_impl(ty),
+                    None => TyFingerprint::Unit,
                 }
             }
             TyKind::AssociatedType(_, _)

crates/hir_ty/src/tests.rs

@@ -195,10 +195,9 @@ fn check_impl(ra_fixture: &str, allow_none: bool, only_types: bool, display_sour
                 mismatch.expected.display_test(&db),
                 mismatch.actual.display_test(&db)
             );
-            if let Some(annotation) = mismatches.remove(&range) {
-                assert_eq!(actual, annotation);
-            } else {
-                format_to!(unexpected_type_mismatches, "{:?}: {}\n", range.range, actual);
+            match mismatches.remove(&range) {
+                Some(annotation) => assert_eq!(actual, annotation),
+                None => format_to!(unexpected_type_mismatches, "{:?}: {}\n", range.range, actual),
             }
         }
         for (expr, mismatch) in inference_result.expr_type_mismatches() {
@@ -215,10 +214,9 @@ fn check_impl(ra_fixture: &str, allow_none: bool, only_types: bool, display_sour
                 mismatch.expected.display_test(&db),
                 mismatch.actual.display_test(&db)
             );
-            if let Some(annotation) = mismatches.remove(&range) {
-                assert_eq!(actual, annotation);
-            } else {
-                format_to!(unexpected_type_mismatches, "{:?}: {}\n", range.range, actual);
+            match mismatches.remove(&range) {
+                Some(annotation) => assert_eq!(actual, annotation),
+                None => format_to!(unexpected_type_mismatches, "{:?}: {}\n", range.range, actual),
             }
         }
     }