Port default command (#848)

crates/nu-command/src/default_context.rs

@@ -57,6 +57,7 @@ pub fn create_default_context(cwd: impl AsRef<Path>) -> EngineState {
             Collect,
             Columns,
             Compact,
+            Default,
             Drop,
             DropColumn,
             DropNth,

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

@@ -0,0 +1,100 @@
+use nu_engine::CallExt;
+use nu_protocol::ast::Call;
+use nu_protocol::engine::{Command, EngineState, Stack};
+use nu_protocol::{Category, Example, PipelineData, Signature, Spanned, SyntaxShape, Value};
+
+#[derive(Clone)]
+pub struct Default;
+
+impl Command for Default {
+    fn name(&self) -> &str {
+        "default"
+    }
+
+    fn signature(&self) -> Signature {
+        Signature::build("default")
+            .required("column name", SyntaxShape::String, "the name of the column")
+            .required(
+                "column value",
+                SyntaxShape::Any,
+                "the value of the column to default",
+            )
+            .category(Category::Filters)
+    }
+
+    fn usage(&self) -> &str {
+        "Sets a default row's column if missing."
+    }
+
+    fn run(
+        &self,
+        engine_state: &EngineState,
+        stack: &mut Stack,
+        call: &Call,
+        input: PipelineData,
+    ) -> Result<nu_protocol::PipelineData, nu_protocol::ShellError> {
+        default(engine_state, stack, call, input)
+    }
+
+    fn examples(&self) -> Vec<Example> {
+        vec![Example {
+            description: "Give a default 'target' to all file entries",
+            example: "ls -la | default target 'nothing'",
+            result: None,
+        }]
+    }
+}
+
+fn default(
+    engine_state: &EngineState,
+    stack: &mut Stack,
+    call: &Call,
+    input: PipelineData,
+) -> Result<nu_protocol::PipelineData, nu_protocol::ShellError> {
+    let column: Spanned<String> = call.req(engine_state, stack, 0)?;
+    let value: Value = call.req(engine_state, stack, 1)?;
+
+    let ctrlc = engine_state.ctrlc.clone();
+
+    input.map(
+        move |item| match item {
+            Value::Record {
+                mut cols,
+                mut vals,
+                span,
+            } => {
+                let mut idx = 0;
+                let mut found = false;
+
+                while idx < cols.len() {
+                    if cols[idx] == column.item && matches!(vals[idx], Value::Nothing { .. }) {
+                        vals[idx] = value.clone();
+                        found = true;
+                    }
+                    idx += 1;
+                }
+
+                if !found {
+                    cols.push(column.item.clone());
+                    vals.push(value.clone());
+                }
+
+                Value::Record { cols, vals, span }
+            }
+            _ => item,
+        },
+        ctrlc,
+    )
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_examples() {
+        use crate::test_examples;
+
+        test_examples(Default {})
+    }
+}

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

@@ -4,6 +4,7 @@ mod append;
 mod collect;
 mod columns;
 mod compact;
+mod default;
 mod drop;
 mod each;
 mod empty;
@@ -43,6 +44,7 @@ pub use append::Append;
 pub use collect::Collect;
 pub use columns::Columns;
 pub use compact::Compact;
+pub use default::Default;
 pub use drop::*;
 pub use each::Each;
 pub use empty::Empty;