diff --git a/src/librustc_attr/builtin.rs b/src/librustc_attr/builtin.rs
index ab5a844e58f..c2b2e7ce59f 100644
--- a/src/librustc_attr/builtin.rs
+++ b/src/librustc_attr/builtin.rs
@@ -98,7 +98,7 @@ pub fn find_unwind_attr(diagnostic: Option<&Handler>, attrs: &[Attribute]) -> Op
                         }
                     }
 
-                    diagnostic.map(|d| {
+                    if let Some(d) = diagnostic {
                         struct_span_err!(d, attr.span, E0633, "malformed `unwind` attribute input")
                             .span_label(attr.span, "invalid argument")
                             .span_suggestions(
@@ -110,7 +110,7 @@ pub fn find_unwind_attr(diagnostic: Option<&Handler>, attrs: &[Attribute]) -> Op
                                 Applicability::MachineApplicable,
                             )
                             .emit();
-                    });
+                    };
                 }
             }
         }
diff --git a/src/librustc_expand/expand.rs b/src/librustc_expand/expand.rs
index 2618c758ca5..972e75d201b 100644
--- a/src/librustc_expand/expand.rs
+++ b/src/librustc_expand/expand.rs
@@ -1172,10 +1172,10 @@ impl<'a, 'b> MutVisitor for InvocationCollector<'a, 'b> {
             // ignore derives so they remain unused
             let (attr, after_derive) = self.classify_nonitem(&mut expr);
 
-            if attr.is_some() {
+            if let Some(ref attr_value) = attr {
                 // Collect the invoc regardless of whether or not attributes are permitted here
                 // expansion will eat the attribute so it won't error later.
-                attr.as_ref().map(|a| self.cfg.maybe_emit_expr_attr_err(a));
+                self.cfg.maybe_emit_expr_attr_err(attr_value);
 
                 // AstFragmentKind::Expr requires the macro to emit an expression.
                 return self
@@ -1322,8 +1322,8 @@ impl<'a, 'b> MutVisitor for InvocationCollector<'a, 'b> {
             // Ignore derives so they remain unused.
             let (attr, after_derive) = self.classify_nonitem(&mut expr);
 
-            if attr.is_some() {
-                attr.as_ref().map(|a| self.cfg.maybe_emit_expr_attr_err(a));
+            if let Some(ref attr_value) = attr {
+                self.cfg.maybe_emit_expr_attr_err(attr_value);
 
                 return self
                     .collect_attr(
diff --git a/src/librustc_hir/definitions.rs b/src/librustc_hir/definitions.rs
index 033c2973af6..30cddac6aac 100644
--- a/src/librustc_hir/definitions.rs
+++ b/src/librustc_hir/definitions.rs
@@ -246,7 +246,7 @@ impl DefPath {
 
         let mut opt_delimiter = None;
         for component in &self.data {
-            opt_delimiter.map(|d| s.push(d));
+            s.extend(opt_delimiter);
             opt_delimiter = Some('-');
             if component.disambiguator == 0 {
                 write!(s, "{}", component.data.as_symbol()).unwrap();
diff --git a/src/librustc_infer/infer/error_reporting/mod.rs b/src/librustc_infer/infer/error_reporting/mod.rs
index dd1d08a75ae..8b530191065 100644
--- a/src/librustc_infer/infer/error_reporting/mod.rs
+++ b/src/librustc_infer/infer/error_reporting/mod.rs
@@ -755,7 +755,9 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
             },
             ObligationCauseCode::IfExpression(box IfExpressionCause { then, outer, semicolon }) => {
                 err.span_label(then, "expected because of this");
-                outer.map(|sp| err.span_label(sp, "`if` and `else` have incompatible types"));
+                if let Some(sp) = outer {
+                    err.span_label(sp, "`if` and `else` have incompatible types");
+                }
                 if let Some(sp) = semicolon {
                     err.span_suggestion_short(
                         sp,
diff --git a/src/librustc_metadata/creader.rs b/src/librustc_metadata/creader.rs
index fe8fbd50627..e7a863c63cc 100644
--- a/src/librustc_metadata/creader.rs
+++ b/src/librustc_metadata/creader.rs
@@ -101,9 +101,15 @@ fn dump_crates(cstore: &CStore) {
         info!("  hash: {}", data.hash());
         info!("  reqd: {:?}", data.dep_kind());
         let CrateSource { dylib, rlib, rmeta } = data.source();
-        dylib.as_ref().map(|dl| info!("  dylib: {}", dl.0.display()));
-        rlib.as_ref().map(|rl| info!("   rlib: {}", rl.0.display()));
-        rmeta.as_ref().map(|rl| info!("   rmeta: {}", rl.0.display()));
+        if let Some(dylib) = dylib {
+            info!("  dylib: {}", dylib.0.display());
+        }
+        if let Some(rlib) = rlib {
+            info!("   rlib: {}", rlib.0.display());
+        }
+        if let Some(rmeta) = rmeta {
+            info!("   rmeta: {}", rmeta.0.display());
+        }
     });
 }
 
diff --git a/src/librustc_mir_build/build/matches/mod.rs b/src/librustc_mir_build/build/matches/mod.rs
index 10ffc81f179..b9d61458a83 100644
--- a/src/librustc_mir_build/build/matches/mod.rs
+++ b/src/librustc_mir_build/build/matches/mod.rs
@@ -1388,7 +1388,9 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         }
 
         // Insert a Shallow borrow of any places that is switched on.
-        fake_borrows.as_mut().map(|fb| fb.insert(match_place));
+        if let Some(fb) = fake_borrows {
+            fb.insert(match_place);
+        }
 
         // perform the test, branching to one of N blocks. For each of
         // those N possible outcomes, create a (initially empty)
diff --git a/src/librustc_parse/parser/mod.rs b/src/librustc_parse/parser/mod.rs
index b987813e38d..9264fc8a735 100644
--- a/src/librustc_parse/parser/mod.rs
+++ b/src/librustc_parse/parser/mod.rs
@@ -1206,8 +1206,8 @@ pub fn emit_unclosed_delims(unclosed_delims: &mut Vec<UnmatchedBrace>, sess: &Pa
     *sess.reached_eof.borrow_mut() |=
         unclosed_delims.iter().any(|unmatched_delim| unmatched_delim.found_delim.is_none());
     for unmatched in unclosed_delims.drain(..) {
-        make_unclosed_delims_error(unmatched, sess).map(|mut e| {
+        if let Some(mut e) = make_unclosed_delims_error(unmatched, sess) {
             e.emit();
-        });
+        }
     }
 }
diff --git a/src/librustc_passes/loops.rs b/src/librustc_passes/loops.rs
index 23a605bef0c..09b3d44020d 100644
--- a/src/librustc_passes/loops.rs
+++ b/src/librustc_passes/loops.rs
@@ -68,7 +68,9 @@ impl<'a, 'hir> Visitor<'hir> for CheckLoopVisitor<'a, 'hir> {
                 self.with_context(LabeledBlock, |v| v.visit_block(&b));
             }
             hir::ExprKind::Break(label, ref opt_expr) => {
-                opt_expr.as_ref().map(|e| self.visit_expr(e));
+                if let Some(e) = opt_expr {
+                    self.visit_expr(e);
+                }
 
                 if self.require_label_in_labeled_block(e.span, &label, "break") {
                     // If we emitted an error about an unlabeled break in a labeled
diff --git a/src/librustc_query_system/query/job.rs b/src/librustc_query_system/query/job.rs
index de6dc81d868..5150b278a77 100644
--- a/src/librustc_query_system/query/job.rs
+++ b/src/librustc_query_system/query/job.rs
@@ -133,7 +133,11 @@ impl<CTX: QueryContext> QueryJob<CTX> {
     /// as there are no concurrent jobs which could be waiting on us
     pub fn signal_complete(self) {
         #[cfg(parallel_compiler)]
-        self.latch.map(|latch| latch.set());
+        {
+            if let Some(latch) = self.latch {
+                latch.set();
+            }
+        }
     }
 }
 
diff --git a/src/librustc_resolve/late.rs b/src/librustc_resolve/late.rs
index 67713b56369..f369e827a40 100644
--- a/src/librustc_resolve/late.rs
+++ b/src/librustc_resolve/late.rs
@@ -1996,7 +1996,9 @@ impl<'a, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
                     this.visit_expr(cond);
                     this.visit_block(then);
                 });
-                opt_else.as_ref().map(|expr| self.visit_expr(expr));
+                if let Some(expr) = opt_else {
+                    self.visit_expr(expr);
+                }
             }
 
             ExprKind::Loop(ref block, label) => self.resolve_labeled_block(label, expr.id, &block),
diff --git a/src/librustc_resolve/lib.rs b/src/librustc_resolve/lib.rs
index e94d7d6a85f..77aa7230aa8 100644
--- a/src/librustc_resolve/lib.rs
+++ b/src/librustc_resolve/lib.rs
@@ -499,7 +499,9 @@ impl<'a> ModuleData<'a> {
         F: FnMut(&mut R, Ident, Namespace, &'a NameBinding<'a>),
     {
         for (key, name_resolution) in resolver.as_mut().resolutions(self).borrow().iter() {
-            name_resolution.borrow().binding.map(|binding| f(resolver, key.ident, key.ns, binding));
+            if let Some(binding) = name_resolution.borrow().binding {
+                f(resolver, key.ident, key.ns, binding);
+            }
         }
     }
 
diff --git a/src/librustc_target/spec/mod.rs b/src/librustc_target/spec/mod.rs
index 8f3097ad423..d9040463317 100644
--- a/src/librustc_target/spec/mod.rs
+++ b/src/librustc_target/spec/mod.rs
@@ -979,20 +979,21 @@ impl Target {
         macro_rules! key {
             ($key_name:ident) => ( {
                 let name = (stringify!($key_name)).replace("_", "-");
-                obj.find(&name[..]).map(|o| o.as_string()
-                                    .map(|s| base.options.$key_name = s.to_string()));
+                if let Some(s) = obj.find(&name).and_then(Json::as_string) {
+                    base.options.$key_name = s.to_string();
+                }
             } );
             ($key_name:ident, bool) => ( {
                 let name = (stringify!($key_name)).replace("_", "-");
-                obj.find(&name[..])
-                    .map(|o| o.as_boolean()
-                         .map(|s| base.options.$key_name = s));
+                if let Some(s) = obj.find(&name).and_then(Json::as_boolean) {
+                    base.options.$key_name = s;
+                }
             } );
             ($key_name:ident, Option<u64>) => ( {
                 let name = (stringify!($key_name)).replace("_", "-");
-                obj.find(&name[..])
-                    .map(|o| o.as_u64()
-                         .map(|s| base.options.$key_name = Some(s)));
+                if let Some(s) = obj.find(&name).and_then(Json::as_u64) {
+                    base.options.$key_name = Some(s);
+                }
             } );
             ($key_name:ident, MergeFunctions) => ( {
                 let name = (stringify!($key_name)).replace("_", "-");
@@ -1034,19 +1035,19 @@ impl Target {
             } );
             ($key_name:ident, list) => ( {
                 let name = (stringify!($key_name)).replace("_", "-");
-                obj.find(&name[..]).map(|o| o.as_array()
-                    .map(|v| base.options.$key_name = v.iter()
-                        .map(|a| a.as_string().unwrap().to_string()).collect()
-                        )
-                    );
+                if let Some(v) = obj.find(&name).and_then(Json::as_array) {
+                    base.options.$key_name = v.iter()
+                        .map(|a| a.as_string().unwrap().to_string())
+                        .collect();
+                }
             } );
             ($key_name:ident, opt_list) => ( {
                 let name = (stringify!($key_name)).replace("_", "-");
-                obj.find(&name[..]).map(|o| o.as_array()
-                    .map(|v| base.options.$key_name = Some(v.iter()
-                        .map(|a| a.as_string().unwrap().to_string()).collect())
-                        )
-                    );
+                if let Some(v) = obj.find(&name).and_then(Json::as_array) {
+                    base.options.$key_name = Some(v.iter()
+                        .map(|a| a.as_string().unwrap().to_string())
+                        .collect());
+                }
             } );
             ($key_name:ident, optional) => ( {
                 let name = (stringify!($key_name)).replace("_", "-");
diff --git a/src/librustc_typeck/astconv.rs b/src/librustc_typeck/astconv.rs
index 706dca999fa..c7d749815fe 100644
--- a/src/librustc_typeck/astconv.rs
+++ b/src/librustc_typeck/astconv.rs
@@ -213,7 +213,9 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             None,
         );
 
-        assoc_bindings.first().map(|b| Self::prohibit_assoc_ty_binding(self.tcx(), b.span));
+        if let Some(b) = assoc_bindings.first() {
+            Self::prohibit_assoc_ty_binding(self.tcx(), b.span);
+        }
 
         substs
     }
@@ -1095,7 +1097,9 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
     ) -> ty::TraitRef<'tcx> {
         let (substs, assoc_bindings, _) =
             self.create_substs_for_ast_trait_ref(span, trait_def_id, self_ty, trait_segment);
-        assoc_bindings.first().map(|b| AstConv::prohibit_assoc_ty_binding(self.tcx(), b.span));
+        if let Some(b) = assoc_bindings.first() {
+            AstConv::prohibit_assoc_ty_binding(self.tcx(), b.span);
+        }
         ty::TraitRef::new(trait_def_id, substs)
     }
 
diff --git a/src/librustc_typeck/check/demand.rs b/src/librustc_typeck/check/demand.rs
index 7db376b20aa..c75283e419a 100644
--- a/src/librustc_typeck/check/demand.rs
+++ b/src/librustc_typeck/check/demand.rs
@@ -36,7 +36,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     // Requires that the two types unify, and prints an error message if
     // they don't.
     pub fn demand_suptype(&self, sp: Span, expected: Ty<'tcx>, actual: Ty<'tcx>) {
-        self.demand_suptype_diag(sp, expected, actual).map(|mut e| e.emit());
+        if let Some(mut e) = self.demand_suptype_diag(sp, expected, actual) {
+            e.emit();
+        }
     }
 
     pub fn demand_suptype_diag(
diff --git a/src/librustc_typeck/check/mod.rs b/src/librustc_typeck/check/mod.rs
index 51e3bc4cae4..b7e86c0791f 100644
--- a/src/librustc_typeck/check/mod.rs
+++ b/src/librustc_typeck/check/mod.rs
@@ -4492,15 +4492,16 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 _ => Err(ErrorReported),
             };
             if item_name.name != kw::Invalid {
-                self.report_method_error(
+                if let Some(mut e) = self.report_method_error(
                     span,
                     ty,
                     item_name,
                     SelfSource::QPath(qself),
                     error,
                     None,
-                )
-                .map(|mut e| e.emit());
+                ) {
+                    e.emit();
+                }
             }
             result
         });
diff --git a/src/librustc_typeck/check/pat.rs b/src/librustc_typeck/check/pat.rs
index b53ae6acdeb..8e109efbcb5 100644
--- a/src/librustc_typeck/check/pat.rs
+++ b/src/librustc_typeck/check/pat.rs
@@ -104,7 +104,9 @@ impl<'tcx> FnCtxt<'_, 'tcx> {
         actual: Ty<'tcx>,
         ti: TopInfo<'tcx>,
     ) {
-        self.demand_eqtype_pat_diag(cause_span, expected, actual, ti).map(|mut err| err.emit());
+        if let Some(mut err) = self.demand_eqtype_pat_diag(cause_span, expected, actual, ti) {
+            err.emit();
+        }
     }
 }
 
@@ -449,12 +451,12 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         // Subtyping doesn't matter here, as the value is some kind of scalar.
         let demand_eqtype = |x, y| {
             if let Some((_, x_ty, x_span)) = x {
-                self.demand_eqtype_pat_diag(x_span, expected, x_ty, ti).map(|mut err| {
+                if let Some(mut err) = self.demand_eqtype_pat_diag(x_span, expected, x_ty, ti) {
                     if let Some((_, y_ty, y_span)) = y {
                         self.endpoint_has_type(&mut err, y_span, y_ty);
                     }
                     err.emit();
-                });
+                };
             }
         };
         demand_eqtype(lhs, rhs);
@@ -852,8 +854,12 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
         // Type-check the tuple struct pattern against the expected type.
         let diag = self.demand_eqtype_pat_diag(pat.span, expected, pat_ty, ti);
-        let had_err = diag.is_some();
-        diag.map(|mut err| err.emit());
+        let had_err = if let Some(mut err) = diag {
+            err.emit();
+            true
+        } else {
+            false
+        };
 
         // Type-check subpatterns.
         if subpats.len() == variant.fields.len()
diff --git a/src/librustc_typeck/check/writeback.rs b/src/librustc_typeck/check/writeback.rs
index 56714a4fa67..c5bf151bc1e 100644
--- a/src/librustc_typeck/check/writeback.rs
+++ b/src/librustc_typeck/check/writeback.rs
@@ -165,12 +165,18 @@ impl<'cx, 'tcx> WritebackCx<'cx, 'tcx> {
                         hir::ExprKind::Binary(..) => {
                             if !op.node.is_by_value() {
                                 let mut adjustments = tables.adjustments_mut();
-                                adjustments.get_mut(lhs.hir_id).map(|a| a.pop());
-                                adjustments.get_mut(rhs.hir_id).map(|a| a.pop());
+                                if let Some(a) = adjustments.get_mut(lhs.hir_id) {
+                                    a.pop();
+                                }
+                                if let Some(a) = adjustments.get_mut(rhs.hir_id) {
+                                    a.pop();
+                                }
                             }
                         }
                         hir::ExprKind::AssignOp(..) => {
-                            tables.adjustments_mut().get_mut(lhs.hir_id).map(|a| a.pop());
+                            if let Some(a) = tables.adjustments_mut().get_mut(lhs.hir_id) {
+                                a.pop();
+                            }
                         }
                         _ => {}
                     }
@@ -215,7 +221,7 @@ impl<'cx, 'tcx> WritebackCx<'cx, 'tcx> {
                     tables.type_dependent_defs_mut().remove(e.hir_id);
                     tables.node_substs_mut().remove(e.hir_id);
 
-                    tables.adjustments_mut().get_mut(base.hir_id).map(|a| {
+                    if let Some(a) = tables.adjustments_mut().get_mut(base.hir_id) {
                         // Discard the need for a mutable borrow
 
                         // Extra adjustment made when indexing causes a drop
@@ -229,7 +235,7 @@ impl<'cx, 'tcx> WritebackCx<'cx, 'tcx> {
                             // So the borrow discard actually happens here
                             a.pop();
                         }
-                    });
+                    }
                 }
             }
         }
diff --git a/src/librustdoc/clean/mod.rs b/src/librustdoc/clean/mod.rs
index 4d03bb21cb3..63ab0ef5f17 100644
--- a/src/librustdoc/clean/mod.rs
+++ b/src/librustdoc/clean/mod.rs
@@ -1599,7 +1599,9 @@ impl<'tcx> Clean<Type> for Ty<'tcx> {
                 inline::record_extern_fqn(cx, did, TypeKind::Trait);
 
                 let mut param_names = vec![];
-                reg.clean(cx).map(|b| param_names.push(GenericBound::Outlives(b)));
+                if let Some(b) = reg.clean(cx) {
+                    param_names.push(GenericBound::Outlives(b));
+                }
                 for did in dids {
                     let empty = cx.tcx.intern_substs(&[]);
                     let path =
@@ -1662,10 +1664,9 @@ impl<'tcx> Clean<Type> for Ty<'tcx> {
                             tr
                         } else if let ty::Predicate::TypeOutlives(pred) = *predicate {
                             // these should turn up at the end
-                            pred.skip_binder()
-                                .1
-                                .clean(cx)
-                                .map(|r| regions.push(GenericBound::Outlives(r)));
+                            if let Some(r) = pred.skip_binder().1.clean(cx) {
+                                regions.push(GenericBound::Outlives(r));
+                            }
                             return None;
                         } else {
                             return None;
diff --git a/src/librustdoc/html/toc.rs b/src/librustdoc/html/toc.rs
index 034fb273000..37540295774 100644
--- a/src/librustdoc/html/toc.rs
+++ b/src/librustdoc/html/toc.rs
@@ -94,7 +94,7 @@ impl TocBuilder {
         loop {
             match self.chain.pop() {
                 Some(mut next) => {
-                    this.map(|e| next.children.entries.push(e));
+                    next.children.entries.extend(this);
                     if next.level < level {
                         // this is the parent we want, so return it to
                         // its rightful place.
@@ -105,7 +105,7 @@ impl TocBuilder {
                     }
                 }
                 None => {
-                    this.map(|e| self.top_level.entries.push(e));
+                    self.top_level.entries.extend(this);
                     return;
                 }
             }
diff --git a/src/libstd/sync/mpsc/shared.rs b/src/libstd/sync/mpsc/shared.rs
index c4e929624d7..fd9d61e99c2 100644
--- a/src/libstd/sync/mpsc/shared.rs
+++ b/src/libstd/sync/mpsc/shared.rs
@@ -91,7 +91,7 @@ impl<T> Packet<T> {
     //
     // This can only be called at channel-creation time
     pub fn inherit_blocker(&self, token: Option<SignalToken>, guard: MutexGuard<'_, ()>) {
-        token.map(|token| {
+        if let Some(token) = token {
             assert_eq!(self.cnt.load(Ordering::SeqCst), 0);
             assert_eq!(self.to_wake.load(Ordering::SeqCst), 0);
             self.to_wake.store(unsafe { token.cast_to_usize() }, Ordering::SeqCst);
@@ -118,7 +118,7 @@ impl<T> Packet<T> {
             unsafe {
                 *self.steals.get() = -1;
             }
-        });
+        }
 
         // When the shared packet is constructed, we grabbed this lock. The
         // purpose of this lock is to ensure that abort_selection() doesn't
diff --git a/src/libstd/sync/mpsc/sync.rs b/src/libstd/sync/mpsc/sync.rs
index 3e2050799cc..79123903e92 100644
--- a/src/libstd/sync/mpsc/sync.rs
+++ b/src/libstd/sync/mpsc/sync.rs
@@ -343,8 +343,12 @@ impl<T> Packet<T> {
         mem::drop(guard);
 
         // only outside of the lock do we wake up the pending threads
-        pending_sender1.map(|t| t.signal());
-        pending_sender2.map(|t| t.signal());
+        if let Some(token) = pending_sender1 {
+            token.signal();
+        }
+        if let Some(token) = pending_sender2 {
+            token.signal();
+        }
     }
 
     // Prepares this shared packet for a channel clone, essentially just bumping
@@ -410,7 +414,9 @@ impl<T> Packet<T> {
         while let Some(token) = queue.dequeue() {
             token.signal();
         }
-        waiter.map(|t| t.signal());
+        if let Some(token) = waiter {
+            token.signal();
+        }
     }
 }