Reduce duplication in history path construction (#13475)

# Description
Currently there is a bit of chaos regarding construction of history file
paths. Various pieces of code across a number of crates reimplement the
same/similar logic:
- There is `get_history_path`, but it requires a directory parameter (it
really just joins it with a file name).
- Some places use a const for the directory parameter, others use a
string literal - in all cases the value seems to be `"nushell"`.
- Some places assume the `"nushell"` value, other plumb it down from
close to the top of the call stack.
- Some places use a constant for history file names while others assume
it.

This PR tries to make it so that the history/config path format is
defined in a single places and so dependencies on it are easier to
follow:
- It removes `get_history_path` and adds a `file_path` method to
`HistoryConfig` instead (an extra motivation being, this is a convenient
place that can be used from all creates that need a history file path)
- Adds a `nu_config_dir` function that returns the nushell configuration
directory.
- Updates existing code to rely on the above, effectively removing
duplicate uses of `"nushell"` and `NUSHELL_FOLDER` and assumptions about
file names associated with different history formats

# User-Facing Changes
None

crates/nu-path/src/helpers.rs

@@ -1,3 +1,5 @@
+use std::path::PathBuf;
+
 use crate::AbsolutePathBuf;
 
 pub fn home_dir() -> Option<AbsolutePathBuf> {
@@ -6,27 +8,29 @@ pub fn home_dir() -> Option<AbsolutePathBuf> {
 
 /// Return the data directory for the current platform or XDG_DATA_HOME if specified.
 pub fn data_dir() -> Option<AbsolutePathBuf> {
-    std::env::var("XDG_DATA_HOME")
-        .ok()
-        .and_then(|path| AbsolutePathBuf::try_from(path).ok())
-        .or_else(|| dirs::data_dir().and_then(|path| AbsolutePathBuf::try_from(path).ok()))
-        .map(|path| path.canonicalize().map(Into::into).unwrap_or(path))
+    configurable_dir_path("XDG_DATA_HOME", dirs::data_dir)
 }
 
 /// Return the cache directory for the current platform or XDG_CACHE_HOME if specified.
 pub fn cache_dir() -> Option<AbsolutePathBuf> {
-    std::env::var("XDG_CACHE_HOME")
-        .ok()
-        .and_then(|path| AbsolutePathBuf::try_from(path).ok())
-        .or_else(|| dirs::cache_dir().and_then(|path| AbsolutePathBuf::try_from(path).ok()))
-        .map(|path| path.canonicalize().map(Into::into).unwrap_or(path))
+    configurable_dir_path("XDG_CACHE_HOME", dirs::cache_dir)
 }
 
-/// Return the config directory for the current platform or XDG_CONFIG_HOME if specified.
-pub fn config_dir() -> Option<AbsolutePathBuf> {
-    std::env::var("XDG_CONFIG_HOME")
+/// Return the nushell config directory.
+pub fn nu_config_dir() -> Option<AbsolutePathBuf> {
+    configurable_dir_path("XDG_CONFIG_HOME", dirs::config_dir).map(|mut p| {
+        p.push("nushell");
+        p
+    })
+}
+
+fn configurable_dir_path(
+    name: &'static str,
+    dir: impl FnOnce() -> Option<PathBuf>,
+) -> Option<AbsolutePathBuf> {
+    std::env::var(name)
         .ok()
         .and_then(|path| AbsolutePathBuf::try_from(path).ok())
-        .or_else(|| dirs::config_dir().and_then(|path| AbsolutePathBuf::try_from(path).ok()))
+        .or_else(|| dir().and_then(|path| AbsolutePathBuf::try_from(path).ok()))
         .map(|path| path.canonicalize().map(Into::into).unwrap_or(path))
 }

crates/nu-path/src/lib.rs

@@ -11,7 +11,7 @@ mod trailing_slash;
 
 pub use components::components;
 pub use expansions::{canonicalize_with, expand_path_with, expand_to_real_path, locate_in_dirs};
-pub use helpers::{cache_dir, config_dir, data_dir, home_dir};
+pub use helpers::{cache_dir, data_dir, home_dir, nu_config_dir};
 pub use path::*;
 pub use tilde::expand_tilde;
 pub use trailing_slash::{has_trailing_slash, strip_trailing_slash};