give guidance to reduce scope of constants

src/var-scope.md

@@ -1,6 +1,6 @@
 # Reduce Scope of Variables
 
-Where possible, reduce scope of variables. Do not reduce the scope if it
+Where possible, reduce scope of variables and constants. Do not reduce the scope if it
 conflicts with [Reduce Nesting](nest-less.md).
 
 <table>
@@ -66,3 +66,37 @@ return nil
 
 </td></tr>
 </tbody></table>
+
+Constants do not need to be global unless they are used in multiple functions or files
+or are part of an external contract of the package.
+
+<table>
+<thead><tr><th>Bad</th><th>Good</th></tr></thead>
+<tbody>
+<tr><td>
+
+```go
+const (
+  _defaultPort = 8080
+  _defaultUser = "user"
+)
+
+func Bar() {
+  fmt.Println("Default port", _defaultPort)
+}
+```
+
+</td><td>
+
+```go
+func Bar() {
+  const (
+    defaultPort = 8080
+    defaultUser = "user"
+  )
+  fmt.Println("Default port", defaultPort)
+}
+```
+
+</td></tr>
+</tbody></table>

style.md

@@ -3209,7 +3209,7 @@ be treated differently in different situations (such as serialization).
 
 ### Reduce Scope of Variables
 
-Where possible, reduce scope of variables. Do not reduce the scope if it
+Where possible, reduce scope of variables and constants. Do not reduce the scope if it
 conflicts with [Reduce Nesting](#reduce-nesting).
 
 <table>
@@ -3276,6 +3276,40 @@ return nil
 </td></tr>
 </tbody></table>
 
+Constants do not need to be global unless they are used in multiple functions or files
+or are part of an external contract of the package.
+
+<table>
+<thead><tr><th>Bad</th><th>Good</th></tr></thead>
+<tbody>
+<tr><td>
+
+```go
+const (
+  _defaultPort = 8080
+  _defaultUser = "user"
+)
+
+func Bar() {
+  fmt.Println("Default port", _defaultPort)
+}
+```
+
+</td><td>
+
+```go
+func Bar() {
+  const (
+    defaultPort = 8080
+    defaultUser = "user"
+  )
+  fmt.Println("Default port", defaultPort)
+}
+```
+
+</td></tr>
+</tbody></table>
+
 ### Avoid Naked Parameters
 
 Naked parameters in function calls can hurt readability. Add C-style comments