move get_columns from the table_viewer to a central location (#628)

* get_columns is working in the columns command

* the new location of the get_columns method is nu-protocol/src/column.rs

* reference the new location of the get_columns method

* move get_columns to nu-engine

crates/nu-command/src/filters/columns.rs

@@ -1,3 +1,4 @@
+use nu_engine::column::get_columns;
 use nu_protocol::ast::Call;
 use nu_protocol::engine::{Command, EngineState, Stack};
 use nu_protocol::{
@@ -66,7 +67,7 @@ fn getcol(
             },
             ..,
         ) => {
-            let input_cols = get_input_cols(input_vals);
+            let input_cols = get_columns(&input_vals);
             Ok(input_cols
                 .into_iter()
                 .map(move |x| Value::String { val: x, span })
@@ -74,7 +75,7 @@ fn getcol(
         }
         PipelineData::ListStream(stream, ..) => {
             let v: Vec<_> = stream.into_iter().collect();
-            let input_cols = get_input_cols(v);
+            let input_cols = get_columns(&v);
 
             Ok(input_cols
                 .into_iter()
@@ -89,14 +90,6 @@ fn getcol(
     }
 }
 
-fn get_input_cols(input: Vec<Value>) -> Vec<String> {
-    let rec = input.first();
-    match rec {
-        Some(Value::Record { cols, vals: _, .. }) => cols.to_vec(),
-        _ => vec!["".to_string()],
-    }
-}
-
 #[cfg(test)]
 mod test {
     use super::*;

crates/nu-command/src/viewers/table.rs

@@ -1,5 +1,6 @@
 use lscolors::{LsColors, Style};
 use nu_color_config::{get_color_config, style_primitive};
+use nu_engine::column::get_columns;
 use nu_engine::{env_to_string, CallExt};
 use nu_protocol::ast::{Call, PathMember};
 use nu_protocol::engine::{Command, EngineState, Stack};
@@ -244,22 +245,6 @@ impl Command for Table {
     }
 }
 
-fn get_columns(input: &[Value]) -> Vec<String> {
-    let mut columns = vec![];
-
-    for item in input {
-        if let Value::Record { cols, vals: _, .. } = item {
-            for col in cols {
-                if !columns.contains(col) {
-                    columns.push(col.to_string());
-                }
-            }
-        }
-    }
-
-    columns
-}
-
 fn convert_to_table(
     row_offset: usize,
     input: &[Value],

crates/nu-engine/src/column.rs

@@ -0,0 +1,17 @@
+use nu_protocol::Value;
+
+pub fn get_columns(input: &[Value]) -> Vec<String> {
+    let mut columns = vec![];
+
+    for item in input {
+        if let Value::Record { cols, vals: _, .. } = item {
+            for col in cols {
+                if !columns.contains(col) {
+                    columns.push(col.to_string());
+                }
+            }
+        }
+    }
+
+    columns
+}

crates/nu-engine/src/lib.rs

@@ -1,9 +1,11 @@
 mod call_ext;
+pub mod column;
 mod documentation;
 mod env;
 mod eval;
 
 pub use call_ext::CallExt;
+pub use column::get_columns;
 pub use documentation::{generate_docs, get_brief_help, get_documentation, get_full_help};
 pub use env::*;
 pub use eval::{eval_block, eval_expression, eval_operator};