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).

3 files changed, 4 insertions, 4 deletions

diff --git a/src/libstd/build.rs b/src/libstd/build.rs
index 0831e29bddd..b3851d22841 100644
--- a/src/libstd/build.rs
+++ b/src/libstd/build.rs
@@ -97,8 +97,8 @@ fn build_libbacktrace(target: &str) -> Result<(), ()> {
         .file("../libbacktrace/sort.c")
         .file("../libbacktrace/state.c");
 
-    let any_debug = env::var("RUSTC_DEBUGINFO").unwrap_or(String::new()) == "true" ||
-        env::var("RUSTC_DEBUGINFO_LINES").unwrap_or(String::new()) == "true";
+    let any_debug = env::var("RUSTC_DEBUGINFO").unwrap_or_default() == "true" ||
+        env::var("RUSTC_DEBUGINFO_LINES").unwrap_or_default() == "true";
     build.debug(any_debug);
 
     if target.contains("darwin") {
diff --git a/src/libstd/sys/redox/args.rs b/src/libstd/sys/redox/args.rs
index 556ed77372e..a7c8ade66f0 100644
--- a/src/libstd/sys/redox/args.rs
+++ b/src/libstd/sys/redox/args.rs
@@ -85,7 +85,7 @@ mod imp {
     }
 
     pub fn args() -> Args {
-        let bytes = clone().unwrap_or(Vec::new());
+        let bytes = clone().unwrap_or_default();
         let v: Vec<OsString> = bytes.into_iter().map(|v| {
             OsStringExt::from_vec(v)
         }).collect();
diff --git a/src/libstd/sys/unix/process/process_unix.rs b/src/libstd/sys/unix/process/process_unix.rs
index 9d6d607e3f3..7f1f9353c6d 100644
--- a/src/libstd/sys/unix/process/process_unix.rs
+++ b/src/libstd/sys/unix/process/process_unix.rs
@@ -331,7 +331,7 @@ impl Command {
             cvt(libc::posix_spawnattr_setflags(&mut attrs.0, flags as _))?;
 
             let envp = envp.map(|c| c.as_ptr())
-                .unwrap_or(*sys::os::environ() as *const _);
+                .unwrap_or_else(|| *sys::os::environ() as *const _);
             let ret = libc::posix_spawnp(
                 &mut p.pid,
                 self.get_argv()[0],