Changed unwrap_or to unwrap_or_else in some places.

The discussion seems to have resolved that this lint is a bit "noisy" in
that applying it in all places would result in a reduction in
readability.

A few of the trivial functions (like `Path::new`) are fine to leave
outside of closures.

The general rule seems to be that anything that is obviously an
allocation (`Box`, `Vec`, `vec![]`) should be in a closure, even if it
is a 0-sized allocation.

compiler/rustc_ast/src/attr/mod.rs

@@ -66,7 +66,7 @@ impl NestedMetaItem {
         self.meta_item().and_then(|meta_item| meta_item.ident())
     }
     pub fn name_or_empty(&self) -> Symbol {
-        self.ident().unwrap_or(Ident::invalid()).name
+        self.ident().unwrap_or_else(Ident::invalid).name
     }
 
     /// Gets the string value if `self` is a `MetaItem` and the `MetaItem` is a
@@ -139,7 +139,7 @@ impl Attribute {
         }
     }
     pub fn name_or_empty(&self) -> Symbol {
-        self.ident().unwrap_or(Ident::invalid()).name
+        self.ident().unwrap_or_else(Ident::invalid).name
     }
 
     pub fn value_str(&self) -> Option<Symbol> {
@@ -183,7 +183,7 @@ impl MetaItem {
         if self.path.segments.len() == 1 { Some(self.path.segments[0].ident) } else { None }
     }
     pub fn name_or_empty(&self) -> Symbol {
-        self.ident().unwrap_or(Ident::invalid()).name
+        self.ident().unwrap_or_else(Ident::invalid).name
     }
 
     // Example:

compiler/rustc_builtin_macros/src/test_harness.rs

@@ -282,7 +282,7 @@ fn mk_main(cx: &mut TestCtxt<'_>) -> P<ast::Item> {
     let mut test_runner = cx
         .test_runner
         .clone()
-        .unwrap_or(ecx.path(sp, vec![test_id, Ident::from_str_and_span(runner_name, sp)]));
+        .unwrap_or_else(|| ecx.path(sp, vec![test_id, Ident::from_str_and_span(runner_name, sp)]));
 
     test_runner.span = sp;
 

compiler/rustc_codegen_cranelift/src/bin/cg_clif.rs

@@ -27,8 +27,8 @@ impl rustc_driver::Callbacks for CraneliftPassesCallbacks {
         config.opts.cg.panic = Some(PanicStrategy::Abort);
         config.opts.debugging_opts.panic_abort_tests = true;
         config.opts.maybe_sysroot = Some(
-            config.opts.maybe_sysroot.clone().unwrap_or(
-                std::env::current_exe()
+            config.opts.maybe_sysroot.clone().unwrap_or_else(
+                || std::env::current_exe()
                     .unwrap()
                     .parent()
                     .unwrap()

compiler/rustc_codegen_llvm/src/intrinsic.rs

@@ -979,12 +979,14 @@ fn generic_simd_intrinsic(
 
         // Integer vector <i{in_bitwidth} x in_len>:
         let (i_xn, in_elem_bitwidth) = match in_elem.kind() {
-            ty::Int(i) => {
-                (args[0].immediate(), i.bit_width().unwrap_or(bx.data_layout().pointer_size.bits()))
-            }
-            ty::Uint(i) => {
-                (args[0].immediate(), i.bit_width().unwrap_or(bx.data_layout().pointer_size.bits()))
-            }
+            ty::Int(i) => (
+                args[0].immediate(),
+                i.bit_width().unwrap_or_else(|| bx.data_layout().pointer_size.bits()),
+            ),
+            ty::Uint(i) => (
+                args[0].immediate(),
+                i.bit_width().unwrap_or_else(|| bx.data_layout().pointer_size.bits()),
+            ),
             _ => return_error!(
                 "vector argument `{}`'s element type `{}`, expected integer element type",
                 in_ty,

compiler/rustc_hir/src/definitions.rs

@@ -409,7 +409,7 @@ impl Definitions {
     }
 
     pub fn expansion_that_defined(&self, id: LocalDefId) -> ExpnId {
-        self.expansions_that_defined.get(&id).copied().unwrap_or(ExpnId::root())
+        self.expansions_that_defined.get(&id).copied().unwrap_or_else(ExpnId::root)
     }
 
     pub fn parent_module_of_macro_def(&self, expn_id: ExpnId) -> DefId {

compiler/rustc_metadata/src/rmeta/decoder.rs

@@ -856,7 +856,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
                 .tables
                 .children
                 .get(self, index)
-                .unwrap_or(Lazy::empty())
+                .unwrap_or_else(Lazy::empty)
                 .decode(self)
                 .map(|index| ty::FieldDef {
                     did: self.local_def_id(index),
@@ -888,7 +888,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
                 .tables
                 .children
                 .get(self, item_id)
-                .unwrap_or(Lazy::empty())
+                .unwrap_or_else(Lazy::empty)
                 .decode(self)
                 .map(|index| self.get_variant(&self.kind(index), index, did, tcx.sess))
                 .collect()
@@ -1075,7 +1075,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
 
         // Iterate over all children.
         let macros_only = self.dep_kind.lock().macros_only();
-        let children = self.root.tables.children.get(self, id).unwrap_or(Lazy::empty());
+        let children = self.root.tables.children.get(self, id).unwrap_or_else(Lazy::empty);
         for child_index in children.decode((self, sess)) {
             if macros_only {
                 continue;
@@ -1098,7 +1098,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
                             .tables
                             .children
                             .get(self, child_index)
-                            .unwrap_or(Lazy::empty());
+                            .unwrap_or_else(Lazy::empty);
                         for child_index in child_children.decode((self, sess)) {
                             let kind = self.def_kind(child_index);
                             callback(Export {
@@ -1284,7 +1284,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
     }
 
     fn get_item_variances(&self, id: DefIndex) -> Vec<ty::Variance> {
-        self.root.tables.variances.get(self, id).unwrap_or(Lazy::empty()).decode(self).collect()
+        self.root.tables.variances.get(self, id).unwrap_or_else(Lazy::empty).decode(self).collect()
     }
 
     fn get_ctor_kind(&self, node_id: DefIndex) -> CtorKind {
@@ -1323,7 +1323,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
             .tables
             .attributes
             .get(self, item_id)
-            .unwrap_or(Lazy::empty())
+            .unwrap_or_else(Lazy::empty)
             .decode((self, sess))
             .collect::<Vec<_>>()
     }
@@ -1333,7 +1333,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
             .tables
             .children
             .get(self, id)
-            .unwrap_or(Lazy::empty())
+            .unwrap_or_else(Lazy::empty)
             .decode(self)
             .map(|index| respan(self.get_span(index, sess), self.item_ident(index, sess).name))
             .collect()
@@ -1349,7 +1349,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
                 .tables
                 .inherent_impls
                 .get(self, id)
-                .unwrap_or(Lazy::empty())
+                .unwrap_or_else(Lazy::empty)
                 .decode(self)
                 .map(|index| self.local_def_id(index)),
         )

compiler/rustc_mir/src/borrow_check/region_infer/mod.rs

@@ -582,7 +582,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
             self.check_member_constraints(infcx, &mut errors_buffer);
         }
 
-        let outlives_requirements = outlives_requirements.unwrap_or(vec![]);
+        let outlives_requirements = outlives_requirements.unwrap_or_default();
 
         if outlives_requirements.is_empty() {
             (None, errors_buffer)

compiler/rustc_session/src/session.rs

@@ -1305,7 +1305,7 @@ pub fn build_session(
         early_error(sopts.error_format, &format!("Error loading host specification: {}", e))
     });
 
-    let loader = file_loader.unwrap_or(Box::new(RealFileLoader));
+    let loader = file_loader.unwrap_or_else(|| Box::new(RealFileLoader));
     let hash_kind = sopts.debugging_opts.src_hash_algorithm.unwrap_or_else(|| {
         if target_cfg.is_like_msvc {
             SourceFileHashAlgorithm::Sha1

compiler/rustc_trait_selection/src/traits/select/mod.rs

@@ -279,7 +279,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
     /// tracking is not enabled, just returns an empty vector.
     pub fn take_intercrate_ambiguity_causes(&mut self) -> Vec<IntercrateAmbiguityCause> {
         assert!(self.intercrate);
-        self.intercrate_ambiguity_causes.take().unwrap_or(vec![])
+        self.intercrate_ambiguity_causes.take().unwrap_or_default()
     }
 
     pub fn infcx(&self) -> &'cx InferCtxt<'cx, 'tcx> {

compiler/rustc_typeck/src/check/fn_ctxt/_impl.rs

@@ -118,7 +118,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         closure_def_id: DefId,
     ) -> Vec<DeferredCallResolution<'tcx>> {
         let mut deferred_call_resolutions = self.deferred_call_resolutions.borrow_mut();
-        deferred_call_resolutions.remove(&closure_def_id).unwrap_or(vec![])
+        deferred_call_resolutions.remove(&closure_def_id).unwrap_or_default()
     }
 
     pub fn tag(&self) -> String {

compiler/rustc_typeck/src/check/method/probe.rs

@@ -244,7 +244,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 ProbeScope::AllTraits,
                 |probe_cx| Ok(probe_cx.candidate_method_names()),
             )
-            .unwrap_or(vec![]);
+            .unwrap_or_default();
         method_names
             .iter()
             .flat_map(|&method_name| {

library/std/src/time.rs

@@ -322,7 +322,7 @@ impl Instant {
     /// ```
     #[stable(feature = "checked_duration_since", since = "1.39.0")]
     pub fn saturating_duration_since(&self, earlier: Instant) -> Duration {
-        self.checked_duration_since(earlier).unwrap_or(Duration::new(0, 0))
+        self.checked_duration_since(earlier).unwrap_or_default()
     }
 
     /// Returns the amount of time elapsed since this instant was created.

src/librustdoc/clean/mod.rs

@@ -935,8 +935,7 @@ impl<'a> Clean<Arguments> for (&'a [hir::Ty<'a>], &'a [Ident]) {
                 .iter()
                 .enumerate()
                 .map(|(i, ty)| {
-                    let mut name =
-                        self.1.get(i).map(|ident| ident.to_string()).unwrap_or(String::new());
+                    let mut name = self.1.get(i).map(|ident| ident.to_string()).unwrap_or_default();
                     if name.is_empty() {
                         name = "_".to_string();
                     }

src/librustdoc/html/render/cache.rs

@@ -128,7 +128,7 @@ pub fn build_index(krate: &clean::Crate, cache: &mut Cache) -> String {
         .module
         .as_ref()
         .map(|module| shorten(plain_text_summary(module.doc_value())))
-        .unwrap_or(String::new());
+        .unwrap_or_default();
 
     #[derive(Serialize)]
     struct CrateData<'a> {