refactor: inline fn partial_from in completer (#10705)

# Description
After the addition of the prefix tab completion support, the older
`partial_from` function is left with a single invocation. This PR moves
the code inside the function to the point of invocation.

# User-Facing Changes

No user facing changes.

# Tests + Formatting
Tests are passing.

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

@@ -1,16 +1,12 @@
-use crate::completions::{completion_common::complete_item, Completer, CompletionOptions};
+use crate::completions::{completion_common::complete_item, Completer, CompletionOptions, SortBy};
 use nu_protocol::{
     engine::{EngineState, StateWorkingSet},
     levenshtein_distance, Span,
 };
 use reedline::Suggestion;
-use std::path::Path;
+use std::path::{Path, MAIN_SEPARATOR as SEP};
 use std::sync::Arc;
 
-use super::SortBy;
-
-const SEP: char = std::path::MAIN_SEPARATOR;
-
 #[derive(Clone)]
 pub struct DirectoryCompletion {
     engine_state: Arc<EngineState>,

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

@@ -1,13 +1,13 @@
-use crate::completions::{
-    file_path_completion, partial_from, Completer, CompletionOptions, SortBy,
-};
+use crate::completions::{file_path_completion, Completer, CompletionOptions, SortBy};
 use nu_protocol::{
     engine::{EngineState, StateWorkingSet},
     Span,
 };
 use reedline::Suggestion;
-use std::sync::Arc;
-const SEP: char = std::path::MAIN_SEPARATOR;
+use std::{
+    path::{is_separator, MAIN_SEPARATOR as SEP, MAIN_SEPARATOR_STR},
+    sync::Arc,
+};
 
 #[derive(Clone)]
 pub struct DotNuCompletion {
@@ -30,9 +30,16 @@ impl Completer for DotNuCompletion {
         _: usize,
         options: &CompletionOptions,
     ) -> Vec<Suggestion> {
-        let prefix_str = String::from_utf8_lossy(&prefix).to_string();
+        let prefix_str = String::from_utf8_lossy(&prefix).replace('`', "");
         let mut search_dirs: Vec<String> = vec![];
-        let (base_dir, mut partial) = partial_from(&prefix_str);
+
+        // If prefix_str is only a word we want to search in the current dir
+        let (base, partial) = prefix_str
+            .rsplit_once(is_separator)
+            .unwrap_or((".", &prefix_str));
+        let base_dir = base.replace(is_separator, MAIN_SEPARATOR_STR);
+        let mut partial = partial.to_string();
+        // On windows, this standardizes paths to use \
         let mut is_current_folder = false;
 
         // Fetch the lib dirs
@@ -58,7 +65,8 @@ impl Completer for DotNuCompletion {
             };
 
         // Check if the base_dir is a folder
-        if base_dir != format!(".{SEP}") {
+        // rsplit_once removes the separator
+        if base_dir != "." {
             // Add the base dir into the directories to be searched
             search_dirs.push(base_dir.clone());
 

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

@@ -1,16 +1,12 @@
-use crate::completions::{completion_common::complete_item, Completer, CompletionOptions};
+use crate::completions::{completion_common::complete_item, Completer, CompletionOptions, SortBy};
 use nu_protocol::{
     engine::{EngineState, StateWorkingSet},
     levenshtein_distance, Span,
 };
 use reedline::Suggestion;
-use std::path::{is_separator, Path};
+use std::path::{Path, MAIN_SEPARATOR as SEP};
 use std::sync::Arc;
 
-use super::SortBy;
-
-const SEP: char = std::path::MAIN_SEPARATOR;
-
 #[derive(Clone)]
 pub struct FileCompletion {
     engine_state: Arc<EngineState>,
@@ -106,20 +102,6 @@ impl Completer for FileCompletion {
     }
 }
 
-pub fn partial_from(input: &str) -> (String, String) {
-    let partial = input.replace('`', "");
-
-    // If partial is only a word we want to search in the current dir
-    let (base, rest) = partial.rsplit_once(is_separator).unwrap_or((".", &partial));
-    // On windows, this standardizes paths to use \
-    let mut base = base.replace(is_separator, &SEP.to_string());
-
-    // rsplit_once removes the separator
-    base.push(SEP);
-
-    (base.to_string(), rest.to_string())
-}
-
 pub fn file_path_completion(
     span: nu_protocol::Span,
     partial: &str,

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

@@ -17,6 +17,6 @@ pub use completion_options::{CompletionOptions, MatchAlgorithm, SortBy};
 pub use custom_completions::CustomCompletion;
 pub use directory_completions::DirectoryCompletion;
 pub use dotnu_completions::DotNuCompletion;
-pub use file_completions::{file_path_completion, matches, partial_from, FileCompletion};
+pub use file_completions::{file_path_completion, matches, FileCompletion};
 pub use flag_completions::FlagCompletion;
 pub use variable_completions::VariableCompletion;