Rollup merge of #34268 - zackmdavis:if_let_over_none_unit_arm, r=jseyfried

prefer `if let` to match with `None => ()` arm in some places

Casual grepping revealed some places in the codebase (some of which
antedated `if let`'s December 2014 stabilization in c200ae5a) where we
were using a match with a `None => ()` arm where (in the present
author's opinion) an `if let` conditional would be more readable. (Other
places where matching to the unit value did seem to better express the
intent were left alone.)

It's likely that we don't care about making such trivial,
non-functional, sheerly æsthetic changes.

But if we do, this is a patch.

3 files changed, 28 insertions, 37 deletions

diff --git a/src/libsyntax/parse/parser.rs b/src/libsyntax/parse/parser.rs
index 22cc20b8f8c..341b076e7cf 100644
--- a/src/libsyntax/parse/parser.rs
+++ b/src/libsyntax/parse/parser.rs
@@ -5430,18 +5430,15 @@ impl<'a> Parser<'a> {
                               name: String,
                               id_sp: Span) -> PResult<'a, (ast::ItemKind, Vec<ast::Attribute> )> {
         let mut included_mod_stack = self.sess.included_mod_stack.borrow_mut();
-        match included_mod_stack.iter().position(|p| *p == path) {
-            Some(i) => {
-                let mut err = String::from("circular modules: ");
-                let len = included_mod_stack.len();
-                for p in &included_mod_stack[i.. len] {
-                    err.push_str(&p.to_string_lossy());
-                    err.push_str(" -> ");
-                }
-                err.push_str(&path.to_string_lossy());
-                return Err(self.span_fatal(id_sp, &err[..]));
-            }
-            None => ()
+        if let Some(i) = included_mod_stack.iter().position(|p| *p == path) {
+            let mut err = String::from("circular modules: ");
+            let len = included_mod_stack.len();
+            for p in &included_mod_stack[i.. len] {
+                err.push_str(&p.to_string_lossy());
+                err.push_str(" -> ");
+            }
+            err.push_str(&path.to_string_lossy());
+            return Err(self.span_fatal(id_sp, &err[..]));
         }
         included_mod_stack.push(path.clone());
         drop(included_mod_stack);
diff --git a/src/libsyntax/print/pprust.rs b/src/libsyntax/print/pprust.rs
index 5b9ec924de9..8818acf9aef 100644
--- a/src/libsyntax/print/pprust.rs
+++ b/src/libsyntax/print/pprust.rs
@@ -2459,12 +2459,9 @@ impl<'a> State<'a> {
                     }
                 }
                 self.print_ident(path1.node)?;
-                match *sub {
-                    Some(ref p) => {
-                        word(&mut self.s, "@")?;
-                        self.print_pat(&p)?;
-                    }
-                    None => ()
+                if let Some(ref p) = *sub {
+                    word(&mut self.s, "@")?;
+                    self.print_pat(&p)?;
                 }
             }
             PatKind::TupleStruct(ref path, ref elts, ddpos) => {
@@ -3008,20 +3005,19 @@ impl<'a> State<'a> {
             Some(cm) => cm,
             _ => return Ok(())
         };
-        match self.next_comment() {
-            Some(ref cmnt) => {
-                if (*cmnt).style != comments::Trailing { return Ok(()) }
-                let span_line = cm.lookup_char_pos(span.hi);
-                let comment_line = cm.lookup_char_pos((*cmnt).pos);
-                let mut next = (*cmnt).pos + BytePos(1);
-                match next_pos { None => (), Some(p) => next = p }
-                if span.hi < (*cmnt).pos && (*cmnt).pos < next &&
-                    span_line.line == comment_line.line {
-                        self.print_comment(cmnt)?;
-                        self.cur_cmnt_and_lit.cur_cmnt += 1;
-                    }
+        if let Some(ref cmnt) = self.next_comment() {
+            if (*cmnt).style != comments::Trailing { return Ok(()) }
+            let span_line = cm.lookup_char_pos(span.hi);
+            let comment_line = cm.lookup_char_pos((*cmnt).pos);
+            let mut next = (*cmnt).pos + BytePos(1);
+            if let Some(p) = next_pos {
+                next = p;
+            }
+            if span.hi < (*cmnt).pos && (*cmnt).pos < next &&
+               span_line.line == comment_line.line {
+                self.print_comment(cmnt)?;
+                self.cur_cmnt_and_lit.cur_cmnt += 1;
             }
-            _ => ()
         }
         Ok(())
     }
diff --git a/src/libsyntax/util/interner.rs b/src/libsyntax/util/interner.rs
index 8e20358027b..7295b36af0f 100644
--- a/src/libsyntax/util/interner.rs
+++ b/src/libsyntax/util/interner.rs
@@ -47,9 +47,8 @@ impl<T: Eq + Hash + Clone + 'static> Interner<T> {
 
     pub fn intern(&self, val: T) -> Name {
         let mut map = self.map.borrow_mut();
-        match (*map).get(&val) {
-            Some(&idx) => return idx,
-            None => (),
+        if let Some(&idx) = (*map).get(&val) {
+            return idx;
         }
 
         let mut vect = self.vect.borrow_mut();
@@ -161,9 +160,8 @@ impl StrInterner {
 
     pub fn intern(&self, val: &str) -> Name {
         let mut map = self.map.borrow_mut();
-        match map.get(val) {
-            Some(&idx) => return idx,
-            None => (),
+        if let Some(&idx) = map.get(val) {
+            return idx;
         }
 
         let new_idx = Name(self.len() as u32);