Improve case insensitivity consistency (#10884)

# Description

Add an extension trait `IgnoreCaseExt` to nu_utils which adds some case
insensitivity helpers, and use them throughout nu to improve the
handling of case insensitivity. Proper case folding is done via unicase,
which is already a dependency via mime_guess from nu-command.

In actuality a lot of code still does `to_lowercase`, because unicase
only provides immediate comparison and doesn't expose a `to_folded_case`
yet. And since we do a lot of `contains`/`starts_with`/`ends_with`, it's
not sufficient to just have `eq_ignore_case`. But if we get access in
the future, this makes us ready to use it with a change in one place.

Plus, it's clearer what the purpose is at the call site to call
`to_folded_case` instead of `to_lowercase` if it's exclusively for the
purpose of case insensitive comparison, even if it just does
`to_lowercase` still.

# User-Facing Changes

- Some commands that were supposed to be case insensitive remained only
insensitive to ASCII case (a-z), and now are case insensitive w.r.t.
non-ASCII characters as well.

# Tests + Formatting

- 🟢 `toolkit fmt`
- 🟢 `toolkit clippy`
- 🟢 `toolkit test`
- 🟢 `toolkit test stdlib`

---------

Co-authored-by: Stefan Holderbach <sholderbach@users.noreply.github.com>

crates/nu-cli/src/completions/custom_completions.rs

@@ -5,6 +5,7 @@ use nu_protocol::{
     engine::{EngineState, Stack, StateWorkingSet},
     PipelineData, Span, Type, Value,
 };
+use nu_utils::IgnoreCaseExt;
 use reedline::Suggestion;
 use std::collections::HashMap;
 use std::sync::Arc;
@@ -153,8 +154,8 @@ fn filter(prefix: &[u8], items: Vec<Suggestion>, options: &CompletionOptions) ->
                 (true, true) => it.value.as_bytes().starts_with(prefix),
                 (true, false) => it.value.contains(std::str::from_utf8(prefix).unwrap_or("")),
                 (false, positional) => {
-                    let value = it.value.to_lowercase();
-                    let prefix = std::str::from_utf8(prefix).unwrap_or("").to_lowercase();
+                    let value = it.value.to_folded_case();
+                    let prefix = std::str::from_utf8(prefix).unwrap_or("").to_folded_case();
                     if positional {
                         value.starts_with(&prefix)
                     } else {

crates/nu-cli/src/completions/file_completions.rs

@@ -6,6 +6,7 @@ use nu_protocol::{
     engine::{EngineState, StateWorkingSet},
     levenshtein_distance, Span,
 };
+use nu_utils::IgnoreCaseExt;
 use reedline::Suggestion;
 use std::path::{Path, MAIN_SEPARATOR as SEP};
 use std::sync::Arc;
@@ -125,7 +126,7 @@ pub fn matches(partial: &str, from: &str, options: &CompletionOptions) -> bool {
     if !options.case_sensitive {
         return options
             .match_algorithm
-            .matches_str(&from.to_ascii_lowercase(), &partial.to_ascii_lowercase());
+            .matches_str(&from.to_folded_case(), &partial.to_folded_case());
     }
 
     options.match_algorithm.matches_str(from, partial)

crates/nu-cli/src/completions/variable_completions.rs

@@ -44,9 +44,7 @@ impl Completer for VariableCompletion {
     ) -> Vec<Suggestion> {
         let mut output = vec![];
         let builtins = ["$nu", "$in", "$env"];
-        let var_str = std::str::from_utf8(&self.var_context.0)
-            .unwrap_or("")
-            .to_lowercase();
+        let var_str = std::str::from_utf8(&self.var_context.0).unwrap_or("");
         let var_id = working_set.find_variable(&self.var_context.0);
         let current_span = reedline::Span {
             start: span.start - offset,
@@ -57,7 +55,7 @@ impl Completer for VariableCompletion {
         // Completions for the given variable
         if !var_str.is_empty() {
             // Completion for $env.<tab>
-            if var_str.as_str() == "$env" {
+            if var_str == "$env" {
                 let env_vars = self.stack.get_env_vars(&self.engine_state);
 
                 // Return nested values
@@ -109,7 +107,7 @@ impl Completer for VariableCompletion {
             }
 
             // Completions for $nu.<tab>
-            if var_str.as_str() == "$nu" {
+            if var_str == "$nu" {
                 // Eval nu var
                 if let Ok(nuval) = eval_variable(
                     &self.engine_state,

crates/nu-cli/src/menus/help_completions.rs

@@ -1,5 +1,6 @@
 use nu_engine::documentation::get_flags_section;
 use nu_protocol::{engine::EngineState, levenshtein_distance};
+use nu_utils::IgnoreCaseExt;
 use reedline::{Completer, Suggestion};
 use std::fmt::Write;
 use std::sync::Arc;
@@ -13,21 +14,19 @@ impl NuHelpCompleter {
 
     fn completion_helper(&self, line: &str, pos: usize) -> Vec<Suggestion> {
         let full_commands = self.0.get_signatures_with_examples(false);
+        let folded_line = line.to_folded_case();
 
         //Vec<(Signature, Vec<Example>, bool, bool)> {
         let mut commands = full_commands
             .iter()
             .filter(|(sig, _, _, _, _)| {
-                sig.name.to_lowercase().contains(&line.to_lowercase())
-                    || sig.usage.to_lowercase().contains(&line.to_lowercase())
+                sig.name.to_folded_case().contains(&folded_line)
+                    || sig.usage.to_folded_case().contains(&folded_line)
                     || sig
                         .search_terms
                         .iter()
-                        .any(|term| term.to_lowercase().contains(&line.to_lowercase()))
-                    || sig
-                        .extra_usage
-                        .to_lowercase()
-                        .contains(&line.to_lowercase())
+                        .any(|term| term.to_folded_case().contains(&folded_line))
+                    || sig.extra_usage.to_folded_case().contains(&folded_line)
             })
             .collect::<Vec<_>>();
 

crates/nu-cli/src/reedline_config.rs

@@ -616,7 +616,7 @@ fn add_parsed_keybinding(
     let modifier = match keybinding
         .modifier
         .into_string("", config)
-        .to_lowercase()
+        .to_ascii_lowercase()
         .as_str()
     {
         "control" => KeyModifiers::CONTROL,
@@ -641,7 +641,7 @@ fn add_parsed_keybinding(
     let keycode = match keybinding
         .keycode
         .into_string("", config)
-        .to_lowercase()
+        .to_ascii_lowercase()
         .as_str()
     {
         "backspace" => KeyCode::Backspace,
@@ -728,7 +728,7 @@ fn parse_event(value: &Value, config: &Config) -> Result<Option<ReedlineEvent>,
     match value {
         Value::Record { val: record, .. } => match EventType::try_from_record(record, span)? {
             EventType::Send(value) => event_from_record(
-                value.into_string("", config).to_lowercase().as_str(),
+                value.into_string("", config).to_ascii_lowercase().as_str(),
                 record,
                 config,
                 span,
@@ -736,7 +736,7 @@ fn parse_event(value: &Value, config: &Config) -> Result<Option<ReedlineEvent>,
             .map(Some),
             EventType::Edit(value) => {
                 let edit = edit_from_record(
-                    value.into_string("", config).to_lowercase().as_str(),
+                    value.into_string("", config).to_ascii_lowercase().as_str(),
                     record,
                     config,
                     span,