feat(cell-path): opt-in case insensitivity for cell-path members

- Add `CellPath::String::insensitive: bool`, represented with an exclamation
  mark in `Display`
- Update `into cell-path` and `split cell-path` to take case
  insensitivity into account while constructing and splitting cell-paths

crates/nu-command/src/conversions/into/cell_path.rs

@@ -17,7 +17,12 @@ impl Command for IntoCellPath {
                 (Type::List(Box::new(Type::Any)), Type::CellPath),
                 (
                     Type::List(Box::new(Type::Record(
-                        [("value".into(), Type::Any), ("optional".into(), Type::Bool)].into(),
+                        [
+                            ("value".into(), Type::Any),
+                            ("optional".into(), Type::Bool),
+                            ("insensitive".into(), Type::Bool),
+                        ]
+                        .into(),
                     ))),
                     Type::CellPath,
                 ),
@@ -69,8 +74,8 @@ impl Command for IntoCellPath {
                 example: "'some.path' | split row '.' | into cell-path",
                 result: Some(Value::test_cell_path(CellPath {
                     members: vec![
-                        PathMember::test_string("some".into(), false),
-                        PathMember::test_string("path".into(), false),
+                        PathMember::test_string("some".into(), false, false),
+                        PathMember::test_string("path".into(), false, false),
                     ],
                 })),
             },
@@ -80,9 +85,9 @@ impl Command for IntoCellPath {
                 result: Some(Value::test_cell_path(CellPath {
                     members: vec![
                         PathMember::test_int(5, false),
-                        PathMember::test_string("c".into(), false),
+                        PathMember::test_string("c".into(), false, false),
                         PathMember::test_int(7, false),
-                        PathMember::test_string("h".into(), false),
+                        PathMember::test_string("h".into(), false, false),
                     ],
                 })),
             },
@@ -92,7 +97,7 @@ impl Command for IntoCellPath {
                 result: Some(Value::test_cell_path(CellPath {
                     members: vec![
                         PathMember::test_int(5, true),
-                        PathMember::test_string("c".into(), false),
+                        PathMember::test_string("c".into(), false, false),
                     ],
                 })),
             },
@@ -175,6 +180,12 @@ fn record_to_path_member(
         }
     };
 
+    if let Some(insensitive) = record.get("insensitive") {
+        if insensitive.as_bool()? {
+            member.make_insensitive();
+        }
+    };
+
     Ok(member)
 }
 
@@ -196,7 +207,7 @@ fn value_to_path_member(val: &Value, span: Span) -> Result<PathMember, ShellErro
     let val_span = val.span();
     let member = match val {
         Value::Int { val, .. } => int_to_path_member(*val, val_span)?,
-        Value::String { val, .. } => PathMember::string(val.into(), false, val_span),
+        Value::String { val, .. } => PathMember::string(val.into(), false, false, val_span),
         Value::Record { val, .. } => record_to_path_member(val, val_span, span)?,
         other => {
             return Err(ShellError::CantConvert {

crates/nu-command/src/conversions/split_cell_path.rs

@@ -16,7 +16,12 @@ impl Command for SplitCellPath {
                 (
                     Type::CellPath,
                     Type::List(Box::new(Type::Record(
-                        [("value".into(), Type::Any), ("optional".into(), Type::Bool)].into(),
+                        [
+                            ("value".into(), Type::Any),
+                            ("optional".into(), Type::Bool),
+                            ("insensitive".into(), Type::Bool),
+                        ]
+                        .into(),
                     ))),
                 ),
             ])
@@ -114,19 +119,29 @@ fn split_cell_path(val: CellPath, span: Span) -> Result<Value, ShellError> {
     struct PathMemberRecord {
         value: Value,
         optional: bool,
+        insensitive: bool,
     }
 
     impl PathMemberRecord {
         fn from_path_member(pm: PathMember) -> Self {
-            let (optional, internal_span) = match pm {
-                PathMember::String { optional, span, .. }
-                | PathMember::Int { optional, span, .. } => (optional, span),
+            let (optional, insensitive, internal_span) = match pm {
+                PathMember::String {
+                    optional,
+                    insensitive,
+                    span,
+                    ..
+                } => (optional, insensitive, span),
+                PathMember::Int { optional, span, .. } => (optional, false, span),
             };
             let value = match pm {
                 PathMember::String { val, .. } => Value::string(val, internal_span),
                 PathMember::Int { val, .. } => Value::int(val as i64, internal_span),
             };
-            Self { value, optional }
+            Self {
+                value,
+                optional,
+                insensitive,
+            }
         }
     }
 

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

@@ -15,7 +15,7 @@ pub fn empty(
     if !columns.is_empty() {
         for val in input {
             for column in &columns {
-                if !val.follow_cell_path(&column.members, false)?.is_nothing() {
+                if !val.follow_cell_path(&column.members)?.is_nothing() {
                     return Ok(Value::bool(negate, head).into_pipeline_data());
                 }
             }

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

@@ -14,6 +14,8 @@ pub enum PathMember {
         /// If marked as optional don't throw an error if not found but perform default handling
         /// (e.g. return `Value::Nothing`)
         optional: bool,
+        /// If marked as insensitive, column lookup happens case insensitively
+        insensitive: bool,
     },
     /// Accessing a member by index (i.e. row of a table or item in a list)
     Int {
@@ -34,11 +36,12 @@ impl PathMember {
         }
     }
 
-    pub fn string(val: String, optional: bool, span: Span) -> Self {
+    pub fn string(val: String, optional: bool, insensitive: bool, span: Span) -> Self {
         PathMember::String {
             val,
             span,
             optional,
+            insensitive,
         }
     }
 
@@ -50,10 +53,11 @@ impl PathMember {
         }
     }
 
-    pub fn test_string(val: String, optional: bool) -> Self {
+    pub fn test_string(val: String, optional: bool, insensitive: bool) -> Self {
         PathMember::String {
             val,
             optional,
+            insensitive,
             span: Span::test_data(),
         }
     }
@@ -69,6 +73,16 @@ impl PathMember {
         }
     }
 
+    pub fn make_insensitive(&mut self) {
+        match self {
+            PathMember::String {
+                ref mut insensitive,
+                ..
+            } => *insensitive = true,
+            PathMember::Int { .. } => {}
+        }
+    }
+
     pub fn span(&self) -> Span {
         match self {
             PathMember::String { span, .. } => *span,
@@ -182,6 +196,12 @@ impl CellPath {
         }
     }
 
+    pub fn make_insensitive(&mut self) {
+        for member in &mut self.members {
+            member.make_insensitive();
+        }
+    }
+
     // Formats the cell-path as a column name, i.e. without quoting and optional markers ('?').
     pub fn to_column_name(&self) -> String {
         let mut s = String::new();
@@ -213,14 +233,20 @@ impl Display for CellPath {
                     let question_mark = if *optional { "?" } else { "" };
                     write!(f, ".{val}{question_mark}")?
                 }
-                PathMember::String { val, optional, .. } => {
+                PathMember::String {
+                    val,
+                    optional,
+                    insensitive,
+                    ..
+                } => {
                     let question_mark = if *optional { "?" } else { "" };
+                    let exclamation_mark = if *insensitive { "!" } else { "" };
                     let val = if needs_quoting(val) {
                         &escape_quote_string(val)
                     } else {
                         val
                     };
-                    write!(f, ".{val}{question_mark}")?
+                    write!(f, ".{val}{exclamation_mark}{question_mark}")?
                 }
             }
         }
@@ -243,7 +269,11 @@ mod test {
     fn path_member_partial_ord() {
         assert_eq!(
             Some(Greater),
-            PathMember::test_int(5, true).partial_cmp(&PathMember::test_string("e".into(), true))
+            PathMember::test_int(5, true).partial_cmp(&PathMember::test_string(
+                "e".into(),
+                true,
+                false
+            ))
         );
 
         assert_eq!(
@@ -258,14 +288,20 @@ mod test {
 
         assert_eq!(
             Some(Greater),
-            PathMember::test_string("e".into(), true)
-                .partial_cmp(&PathMember::test_string("e".into(), false))
+            PathMember::test_string("e".into(), true, false).partial_cmp(&PathMember::test_string(
+                "e".into(),
+                false,
+                false
+            ))
         );
 
         assert_eq!(
             Some(Greater),
-            PathMember::test_string("f".into(), true)
-                .partial_cmp(&PathMember::test_string("e".into(), true))
+            PathMember::test_string("f".into(), true, false).partial_cmp(&PathMember::test_string(
+                "e".into(),
+                true,
+                false
+            ))
         );
     }
 }