Auto merge of #55014 - ljedrz:lazyboye_unwraps, r=matthewjasper

Prefer unwrap_or_else to unwrap_or in case of function calls/allocations

The contents of `unwrap_or` are evaluated eagerly, so it's not a good pick in case of function calls and allocations. This PR also changes a few `unwrap_or`s with `unwrap_or_default`.

An added bonus is that in some cases this change also reveals if the object it's called on is an `Option` or a `Result` (based on whether the closure takes an argument).

Author: bors

src/bootstrap/config.rs

@@ -430,7 +430,7 @@ impl Config {
             }
         }).unwrap_or_else(|| TomlConfig::default());
 
-        let build = toml.build.clone().unwrap_or(Build::default());
+        let build = toml.build.clone().unwrap_or_default();
         // set by bootstrap.py
         config.hosts.push(config.build.clone());
         for host in build.host.iter() {
@@ -524,7 +524,7 @@ impl Config {
             set(&mut config.llvm_link_shared, llvm.link_shared);
             config.llvm_targets = llvm.targets.clone();
             config.llvm_experimental_targets = llvm.experimental_targets.clone()
-                .unwrap_or("WebAssembly;RISCV".to_string());
+                .unwrap_or_else(|| "WebAssembly;RISCV".to_string());
             config.llvm_link_jobs = llvm.link_jobs;
             config.llvm_version_suffix = llvm.version_suffix.clone();
             config.llvm_clang_cl = llvm.clang_cl.clone();

src/build_helper/lib.rs

@@ -233,7 +233,8 @@ pub fn native_lib_boilerplate(
     let src_dir = current_dir.join("..").join(src_name);
     rerun_if_changed_anything_in_dir(&src_dir);
 
-    let out_dir = env::var_os("RUSTBUILD_NATIVE_DIR").unwrap_or(env::var_os("OUT_DIR").unwrap());
+    let out_dir = env::var_os("RUSTBUILD_NATIVE_DIR").unwrap_or_else(||
+        env::var_os("OUT_DIR").unwrap());
     let out_dir = PathBuf::from(out_dir).join(out_name);
     t!(fs::create_dir_all(&out_dir));
     if link_name.contains('=') {

src/librustc/hir/lowering.rs

@@ -1598,7 +1598,7 @@ impl<'a> LoweringContext<'a> {
 
         let resolution = self.resolver
             .get_resolution(id)
-            .unwrap_or(PathResolution::new(Def::Err));
+            .unwrap_or_else(|| PathResolution::new(Def::Err));
 
         let proj_start = p.segments.len() - resolution.unresolved_segments();
         let path = P(hir::Path {

src/librustc/lint/levels.rs

@@ -97,7 +97,7 @@ impl LintLevelSets {
 
         // If `level` is none then we actually assume the default level for this
         // lint.
-        let mut level = level.unwrap_or(lint.default_level(sess));
+        let mut level = level.unwrap_or_else(|| lint.default_level(sess));
 
         // If we're about to issue a warning, check at the last minute for any
         // directives against the warnings "lint". If, for example, there's an

src/librustc/lint/mod.rs

@@ -519,7 +519,7 @@ impl LintBuffer {
     }
 
     pub fn take(&mut self, id: ast::NodeId) -> Vec<BufferedEarlyLint> {
-        self.map.remove(&id).unwrap_or(Vec::new())
+        self.map.remove(&id).unwrap_or_default()
     }
 
     pub fn get_any(&self) -> Option<&[BufferedEarlyLint]> {

src/librustc/traits/auto_trait.rs

@@ -498,8 +498,8 @@ impl<'a, 'tcx> AutoTraitFinder<'a, 'tcx> {
                     panic!("Missing lifetime with name {:?} for {:?}", name, region)
                 )
             )
-            .unwrap_or(&"'static".to_owned())
-            .clone()
+            .cloned()
+            .unwrap_or_else(|| "'static".to_owned())
     }
 
     // This is very similar to handle_lifetimes. However, instead of matching ty::Region's

src/librustc/traits/error_reporting.rs

@@ -352,7 +352,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         obligation: &PredicateObligation<'tcx>,
     ) -> OnUnimplementedNote {
         let def_id = self.impl_similar_to(trait_ref, obligation)
-            .unwrap_or(trait_ref.def_id());
+            .unwrap_or_else(|| trait_ref.def_id());
         let trait_ref = *trait_ref.skip_binder();
 
         let mut flags = vec![];
@@ -639,7 +639,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                         let (post_message, pre_message) =
                             self.get_parent_trait_ref(&obligation.cause.code)
                                 .map(|t| (format!(" in `{}`", t), format!("within `{}`, ", t)))
-                            .unwrap_or((String::new(), String::new()));
+                            .unwrap_or_default();
 
                         let OnUnimplementedNote { message, label, note }
                             = self.on_unimplemented_note(trait_ref, obligation);

src/librustc/ty/context.rs

@@ -551,7 +551,7 @@ impl<'tcx> TypeckTables<'tcx> {
 
     pub fn node_substs(&self, id: hir::HirId) -> &'tcx Substs<'tcx> {
         validate_hir_id_for_typeck_tables(self.local_id_root, id, false);
-        self.node_substs.get(&id.local_id).cloned().unwrap_or(Substs::empty())
+        self.node_substs.get(&id.local_id).cloned().unwrap_or_else(|| Substs::empty())
     }
 
     pub fn node_substs_opt(&self, id: hir::HirId) -> Option<&'tcx Substs<'tcx>> {

src/librustc/ty/query/on_disk_cache.rs

@@ -342,7 +342,7 @@ impl<'sess> OnDiskCache<'sess> {
             &self.prev_diagnostics_index,
             "diagnostics");
 
-        diagnostics.unwrap_or(Vec::new())
+        diagnostics.unwrap_or_default()
     }
 
     /// Store a diagnostic emitted during the current compilation session.

src/librustc_codegen_llvm/attributes.rs

@@ -154,7 +154,7 @@ pub fn from_fn_attrs(
     id: Option<DefId>,
 ) {
     let codegen_fn_attrs = id.map(|id| cx.tcx.codegen_fn_attrs(id))
-        .unwrap_or(CodegenFnAttrs::new());
+        .unwrap_or_else(|| CodegenFnAttrs::new());
 
     inline(cx, llfn, codegen_fn_attrs.inline);