Rollup merge of #52658 - Wallacoloo:topics/use-option-methods, r=cramertj

Prefer `Option::map`/etc over `match` wherever it improves clarity

This isn't intended to change behavior anywhere. A lot of times statements like `match x { None => None, Some(y) => [...] }` can be rewritten using `Option::map` or `Option::and_then` in a way that preserves or improves clarity, so that's what I've done here.

I think it's particularly valuable to keep things in `libcore` and `libstd` pretty/idiomatic since it's not uncommon to follow the `[src]` links when browsing the rust-lang.org docs for std/core. If there's any concern about pushing style-based changes though, I'll happily back out the non-std/core commits here.

3 files changed, 6 insertions, 13 deletions

diff --git a/src/libstd/net/parser.rs b/src/libstd/net/parser.rs
index ae5037cc44e..008c5da171f 100644
--- a/src/libstd/net/parser.rs
+++ b/src/libstd/net/parser.rs
@@ -53,10 +53,7 @@ impl<'a> Parser<'a> {
         F: FnOnce(&mut Parser) -> Option<T>,
     {
         self.read_atomically(move |p| {
-            match cb(p) {
-                Some(x) => if p.is_eof() {Some(x)} else {None},
-                None => None,
-            }
+            cb(p).filter(|_| p.is_eof())
         })
     }
 
diff --git a/src/libstd/path.rs b/src/libstd/path.rs
index 0c60129494d..688a7e99f10 100644
--- a/src/libstd/path.rs
+++ b/src/libstd/path.rs
@@ -1065,10 +1065,7 @@ impl<'a> Iterator for Ancestors<'a> {
 
     fn next(&mut self) -> Option<Self::Item> {
         let next = self.next;
-        self.next = match next {
-            Some(path) => path.parent(),
-            None => None,
-        };
+        self.next = next.and_then(Path::parent);
         next
     }
 }
diff --git a/src/libstd/sys_common/backtrace.rs b/src/libstd/sys_common/backtrace.rs
index 61d7ed463dd..2db47bd5947 100644
--- a/src/libstd/sys_common/backtrace.rs
+++ b/src/libstd/sys_common/backtrace.rs
@@ -156,16 +156,15 @@ pub fn log_enabled() -> Option<PrintFormat> {
         _ => return Some(PrintFormat::Full),
     }
 
-    let val = match env::var_os("RUST_BACKTRACE") {
-        Some(x) => if &x == "0" {
+    let val = env::var_os("RUST_BACKTRACE").and_then(|x|
+        if &x == "0" {
             None
         } else if &x == "full" {
             Some(PrintFormat::Full)
         } else {
             Some(PrintFormat::Short)
-        },
-        None => None,
-    };
+        }
+    );
     ENABLED.store(match val {
         Some(v) => v as isize,
         None => 1,