Use slices directly instead of &Vec (#10328)

Simplifies the signature, makes it more flexible.
Detected a few unnecessary allocations in the process.

crates/nu-command/src/debug/inspect_table.rs

@@ -235,7 +235,7 @@ mod util {
         }
     }
 
-    fn convert_records_to_dataset(cols: &Vec<String>, records: Vec<Value>) -> Vec<Vec<String>> {
+    fn convert_records_to_dataset(cols: &[String], records: Vec<Value>) -> Vec<Vec<String>> {
         if !cols.is_empty() {
             create_table_for_record(cols, &records)
         } else if cols.is_empty() && records.is_empty() {

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

@@ -294,7 +294,7 @@ fn record_matches_regex(values: &[Value], re: &Regex, config: &Config) -> bool {
 
 #[allow(clippy::too_many_arguments)]
 fn highlight_terms_in_record_with_search_columns(
-    search_cols: &Vec<String>,
+    search_cols: &[String],
     record: &Record,
     span: Span,
     config: &Config,
@@ -507,7 +507,7 @@ fn value_should_be_printed(
     filter_config: &Config,
     lower_terms: &[Value],
     span: Span,
-    columns_to_search: &Vec<String>,
+    columns_to_search: &[String],
     invert: bool,
 ) -> bool {
     let lower_value = Value::string(value.into_string("", filter_config).to_lowercase(), span);
@@ -561,7 +561,7 @@ fn term_equals_value(term: &Value, value: &Value, span: Span) -> bool {
 
 fn record_matches_term(
     record: &Record,
-    columns_to_search: &Vec<String>,
+    columns_to_search: &[String],
     filter_config: &Config,
     term: &Value,
     span: Span,

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

@@ -210,7 +210,7 @@ pub fn group_no_grouper(values: Vec<Value>, span: Span) -> Result<Value, ShellEr
 
 // TODO: refactor this, it's a bit of a mess
 fn group_closure(
-    values: &Vec<Value>,
+    values: &[Value],
     span: Span,
     block: Option<Closure>,
     stack: &mut Stack,
@@ -219,7 +219,7 @@ fn group_closure(
 ) -> Result<Value, ShellError> {
     let error_key = "error";
     let mut keys: Vec<Result<String, ShellError>> = vec![];
-    let value_list = Value::list(values.clone(), span);
+    let value_list = Value::list(values.to_vec(), span);
 
     for value in values {
         if let Some(capture_block) = &block {

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

@@ -23,8 +23,6 @@ enum IncludeInner {
     Yes,
 }
 
-const EMPTY_COL_NAMES: &Vec<String> = &vec![];
-
 impl Command for Join {
     fn name(&self) -> &str {
         "join"
@@ -142,8 +140,8 @@ fn join_type(call: &Call) -> Result<JoinType, nu_protocol::ShellError> {
 }
 
 fn join(
-    left: &Vec<Value>,
-    right: &Vec<Value>,
+    left: &[Value],
+    right: &[Value],
     left_join_key: &str,
     right_join_key: &str,
     join_type: JoinType,
@@ -248,7 +246,7 @@ fn join(
 #[allow(clippy::too_many_arguments)]
 fn join_rows(
     result: &mut Vec<Value>,
-    this: &Vec<Value>,
+    this: &[Value],
     this_join_key: &str,
     other: HashMap<String, Vec<&Record>>,
     other_keys: &[String],
@@ -323,20 +321,20 @@ fn join_rows(
 
 // Return column names (i.e. ordered keys from the first row; we assume that
 // these are the same for all rows).
-fn column_names(table: &[Value]) -> &Vec<String> {
+fn column_names(table: &[Value]) -> &[String] {
     table
         .iter()
         .find_map(|val| match val {
-            Value::Record { val, .. } => Some(&val.cols),
+            Value::Record { val, .. } => Some(&*val.cols),
             _ => None,
         })
-        .unwrap_or(EMPTY_COL_NAMES)
+        .unwrap_or_default()
 }
 
 // Create a map from value in `on` column to a list of the rows having that
 // value.
 fn lookup_table<'a>(
-    rows: &'a Vec<Value>,
+    rows: &'a [Value],
     on: &str,
     sep: &str,
     cap: usize,

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

@@ -76,7 +76,7 @@ impl Command for UniqBy {
         let metadata = input.metadata();
 
         let vec: Vec<_> = input.into_iter().collect();
-        match validate(vec.clone(), &columns, call.head) {
+        match validate(&vec, &columns, call.head) {
             Ok(_) => {}
             Err(err) => {
                 return Err(err);
@@ -113,7 +113,7 @@ impl Command for UniqBy {
     }
 }
 
-fn validate(vec: Vec<Value>, columns: &Vec<String>, span: Span) -> Result<(), ShellError> {
+fn validate(vec: &[Value], columns: &[String], span: Span) -> Result<(), ShellError> {
     let first = vec.first();
     if let Some(v) = first {
         let val_span = v.span();
@@ -129,7 +129,7 @@ fn validate(vec: Vec<Value>, columns: &Vec<String>, span: Span) -> Result<(), Sh
                 ));
             }
 
-            if let Some(nonexistent) = nonexistent_column(columns.clone(), record.cols.clone()) {
+            if let Some(nonexistent) = nonexistent_column(columns, &record.cols) {
                 return Err(ShellError::CantFindColumn {
                     col_name: nonexistent,
                     span,

crates/nu-command/src/formats/to/delimited.rs

@@ -46,7 +46,7 @@ fn record_to_delimited(
 }
 
 fn table_to_delimited(
-    vals: &Vec<Value>,
+    vals: &[Value],
     span: Span,
     separator: char,
     config: &Config,

crates/nu-command/src/sort_utils.rs

@@ -77,8 +77,7 @@ pub fn sort(
                 ));
             }
 
-            if let Some(nonexistent) = nonexistent_column(sort_columns.clone(), record.cols.clone())
-            {
+            if let Some(nonexistent) = nonexistent_column(&sort_columns, &record.cols) {
                 return Err(ShellError::CantFindColumn {
                     col_name: nonexistent,
                     span,