Make user_name_to_file_name public, tweak signature

The function now takes a closure instead of a hashset, and now works
with any AsRef<str> type, anod not just Name; this makes it more
suitable as public API.

src/lib.rs

@@ -104,4 +104,5 @@ pub use identifier::Identifier;
 pub use kerning::Kerning;
 pub use layer::{Layer, LayerSet};
 pub use shared_types::{Color, Plist};
+pub use util::user_name_to_file_name;
 pub use write::{QuoteChar, WriteOptions};

src/util.rs

@@ -19,31 +19,39 @@ pub(crate) fn recursive_sort_plist_keys(plist: &mut plist::Dictionary) {
 
 /// Given a glyph `name`, return an appropriate file name.
 pub(crate) fn default_file_name_for_glyph_name(name: &Name, existing: &HashSet<String>) -> PathBuf {
-    user_name_to_file_name(name, "", ".glif", existing)
+    user_name_to_file_name(name, "", ".glif", |name| !existing.contains(name))
 }
 
 /// Given a layer `name`, return an appropriate file name.
 pub(crate) fn default_file_name_for_layer_name(name: &Name, existing: &HashSet<String>) -> PathBuf {
-    user_name_to_file_name(name, "glyphs.", "", existing)
+    user_name_to_file_name(name, "glyphs.", "", |name| !existing.contains(name))
 }
 
 /// Given a `name`, return an appropriate file name.
 ///
-/// Expects `existing` to be a set of paths (potentially lossily) converted to
-/// _lowercased [`String`]s_. The file names are going to end up in a UTF-8
-/// encoded Apple property list XML file, so file names will be treated as
-/// Unicode strings.
+/// This file name is computed via the [Common User Name to File Name Algorithm][algo]
+/// defined in the UFO spec.
+///
+/// the `prefix` and `suffix` fields will be added to the start and end of the
+/// generated path; for instance the `suffix` might be a file extension.
+///
+/// The `accept_path` closure is a way of indicating whether or not a candidate
+/// path should be used. In general, this involves ensuring that the candidate path
+/// does not already exist. Paths are always lowercased, and case insensitive.
 ///
 /// # Panics
 ///
 /// Panics if a case-insensitive file name clash was detected and no unique
 /// value could be created after 99 numbering attempts.
-fn user_name_to_file_name(
-    name: &Name,
+///
+/// [algo]: https://unifiedfontobject.org/versions/ufo3/conventions/#common-user-name-to-file-name-algorithm
+pub fn user_name_to_file_name(
+    name: impl AsRef<str>,
     prefix: &str,
     suffix: &str,
-    existing: &HashSet<String>,
+    mut accept_path: impl FnMut(&str) -> bool,
 ) -> PathBuf {
+    let name = name.as_ref();
     let mut result = String::with_capacity(prefix.len() + name.len() + suffix.len());
 
     // Filter illegal characters from name.
@@ -136,7 +144,7 @@ fn user_name_to_file_name(
     // second way should one exhaust them, but it is unlikely to be needed in
     // practice. 1e15 numbers is a ridicuously high number where holding all
     // those glyph names in memory would exhaust it.
-    if existing.contains(&result.to_lowercase()) {
+    if !accept_path(&result.to_lowercase()) {
         // First, cut off the suffix (plus the space needed for the number
         // counter if necessary).
         const NUMBER_LEN: usize = 2;
@@ -155,7 +163,8 @@ fn user_name_to_file_name(
         for counter in 1..100u8 {
             write!(&mut result, "{:0>2}", counter).unwrap();
             result.push_str(suffix);
-            if !existing.contains(&result.to_lowercase()) {
+            if accept_path(&result.to_lowercase()) {
+                //if !existing.contains(&result.to_lowercase()) {
                 found_unique = true;
                 break;
             }
@@ -184,9 +193,11 @@ mod tests {
 
     fn file_name(name: &str, prefix: &str, suffix: &str) -> String {
         let container: HashSet<String> = HashSet::new();
-        user_name_to_file_name(&Name::new_raw(name), prefix, suffix, &container)
-            .to_string_lossy()
-            .to_string()
+        user_name_to_file_name(&Name::new_raw(name), prefix, suffix, |name| {
+            !container.contains(name)
+        })
+        .to_string_lossy()
+        .to_string()
     }
 
     #[test]
@@ -281,7 +292,9 @@ mod tests {
         let mut container = HashSet::new();
         let mut existing = HashSet::new();
         for name in ["Ab", "a_b"] {
-            let path = user_name_to_file_name(&Name::new_raw(name), "", ".glif", &existing);
+            let path = user_name_to_file_name(&Name::new_raw(name), "", ".glif", |name| {
+                !existing.contains(name)
+            });
             existing.insert(path.to_string_lossy().to_string().to_lowercase());
             container.insert(path.to_string_lossy().to_string());
         }
@@ -298,7 +311,9 @@ mod tests {
         let mut container = HashSet::new();
         let mut existing = HashSet::new();
         for name in ["A".repeat(300), "a_".repeat(150)] {
-            let path = user_name_to_file_name(&Name::new_raw(&name), "", ".glif", &existing);
+            let path = user_name_to_file_name(&Name::new_raw(&name), "", ".glif", |name| {
+                !existing.contains(name)
+            });
             existing.insert(path.to_string_lossy().to_string().to_lowercase());
             container.insert(path.to_string_lossy().to_string());
         }