Allow viewing the source code of blocks (#894)

* Add spans to blocks and view command

* Better description; Cleanup

* Rename "view" command to "view-source"

crates/nu-protocol/src/ast/block.rs

@@ -1,6 +1,6 @@
 use std::ops::{Index, IndexMut};
 
-use crate::{Signature, VarId};
+use crate::{Signature, Span, VarId};
 
 use super::Statement;
 
@@ -10,6 +10,7 @@ pub struct Block {
     pub stmts: Vec<Statement>,
     pub captures: Vec<VarId>,
     pub redirect_env: bool,
+    pub span: Option<Span>, // None option encodes no span to avoid using test_span()
 }
 
 impl Block {
@@ -49,6 +50,7 @@ impl Block {
             stmts: vec![],
             captures: vec![],
             redirect_env: false,
+            span: None,
         }
     }
 }
@@ -63,6 +65,7 @@ where
             stmts: stmts.collect(),
             captures: vec![],
             redirect_env: false,
+            span: None,
         }
     }
 }

crates/nu-protocol/src/overlay.rs

@@ -1,4 +1,4 @@
-use crate::{BlockId, DeclId};
+use crate::{BlockId, DeclId, Span};
 
 use indexmap::IndexMap;
 
@@ -10,6 +10,7 @@ use indexmap::IndexMap;
 pub struct Overlay {
     pub decls: IndexMap<Vec<u8>, DeclId>,
     pub env_vars: IndexMap<Vec<u8>, BlockId>,
+    pub span: Option<Span>,
 }
 
 impl Overlay {
@@ -17,6 +18,15 @@ impl Overlay {
         Overlay {
             decls: IndexMap::new(),
             env_vars: IndexMap::new(),
+            span: None,
+        }
+    }
+
+    pub fn from_span(span: Span) -> Self {
+        Overlay {
+            decls: IndexMap::new(),
+            env_vars: IndexMap::new(),
+            span: Some(span),
         }
     }