Use heck instead of convert_case for nu-derive-value (#13708)

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# Description
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@sholderbach mentioned that I introduced `convert_case` as a dependency
while we already had `heck` for case conversion. So in this PR replaced
the use `convert_case` with `heck`. Mostly I rebuilt the `convert_case`
API with `heck` to work with it as I like the API of `convert_case` more
than `heck`.

# User-Facing Changes
<!-- List of all changes that impact the user experience here. This
helps us keep track of breaking changes. -->
Nothing changed, the use of `convert_case` wasn't exposed anywhere and
all case conversions are still available.

# Tests + Formatting
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No new tests required but my tests in `test_derive` captured some errors
I made while developing this change, (hurray, tests work 🎉)
- 🟢 `toolkit fmt`
- 🟢 `toolkit clippy`
- 🟢 `toolkit test`
- 🟢 `toolkit test stdlib`

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crates/nu-derive-value/Cargo.toml

@@ -18,4 +18,4 @@ proc-macro2 = { workspace = true }
 syn = { workspace = true }
 quote = { workspace = true }
 proc-macro-error = { workspace = true }
-convert_case = { workspace = true }
+heck = { workspace = true }

crates/nu-derive-value/src/attributes.rs

@@ -1,7 +1,6 @@
-use convert_case::Case;
 use syn::{spanned::Spanned, Attribute, Fields, LitStr};
 
-use crate::{error::DeriveError, HELPER_ATTRIBUTE};
+use crate::{case::Case, error::DeriveError, HELPER_ATTRIBUTE};
 
 #[derive(Debug, Default)]
 pub struct ContainerAttributes {
@@ -22,35 +21,19 @@ impl ContainerAttributes {
                 let ident = meta.path.require_ident()?;
                 match ident.to_string().as_str() {
                     "rename_all" => {
-                        // The matched case are all useful variants from `convert_case` with aliases
-                        // that `serde` uses.
                         let case: LitStr = meta.value()?.parse()?;
-                        let case = match case.value().as_str() {
-                            "UPPER CASE" | "UPPER WITH SPACES CASE" => Case::Upper,
-                            "lower case" | "lower with spaces case" => Case::Lower,
-                            "Title Case" => Case::Title,
-                            "camelCase" => Case::Camel,
-                            "PascalCase" | "UpperCamelCase" => Case::Pascal,
-                            "snake_case" => Case::Snake,
-                            "UPPER_SNAKE_CASE" | "SCREAMING_SNAKE_CASE" => Case::UpperSnake,
-                            "kebab-case" => Case::Kebab,
-                            "COBOL-CASE" | "UPPER-KEBAB-CASE" | "SCREAMING-KEBAB-CASE" => {
-                                Case::Cobol
-                            }
-                            "Train-Case" => Case::Train,
-                            "flatcase" | "lowercase" => Case::Flat,
-                            "UPPERFLATCASE" | "UPPERCASE" => Case::UpperFlat,
-                            // Although very funny, we don't support `Case::{Toggle, Alternating}`,
-                            // as we see no real benefit.
-                            c => {
+                        let value_span = case.span();
+                        let case = case.value();
+                        match Case::from_str(&case) {
+                            Some(case) => container_attrs.rename_all = Some(case),
+                            None => {
                                 err = Err(DeriveError::InvalidAttributeValue {
-                                    value_span: case.span(),
-                                    value: Box::new(c.to_string()),
+                                    value_span,
+                                    value: Box::new(case),
                                 });
                                 return Ok(()); // We stored the err in `err`.
                             }
-                        };
-                        container_attrs.rename_all = Some(case);
+                        }
                     }
                     "type_name" => {
                         let type_name: LitStr = meta.value()?.parse()?;

crates/nu-derive-value/src/case.rs

@@ -0,0 +1,72 @@
+use heck::*;
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq)]
+pub enum Case {
+    // directly supported by heck
+    Pascal,
+    Camel,
+    Snake,
+    Kebab,
+    ScreamingSnake,
+    Title,
+    Cobol,
+    Train,
+
+    // custom variants
+    Upper,
+    Lower,
+    Flat,
+    ScreamingFlat,
+}
+
+impl Case {
+    pub fn from_str(s: impl AsRef<str>) -> Option<Self> {
+        match s.as_ref() {
+            // The matched case are all useful variants from `convert_case` with aliases
+            // that `serde` uses.
+            "PascalCase" | "UpperCamelCase" => Case::Pascal,
+            "camelCase" | "lowerCamelCase" => Case::Camel,
+            "snake_case" => Case::Snake,
+            "kebab-case" => Case::Kebab,
+            "SCREAMING_SNAKE_CASE" | "UPPER_SNAKE_CASE" | "SHOUTY_SNAKE_CASE" => {
+                Case::ScreamingSnake
+            }
+            "Title Case" => Case::Title,
+            "COBOL-CASE" | "SCREAMING-KEBAB-CASE" | "UPPER-KEBAB-CASE" => Case::Cobol,
+            "Train-Case" => Case::Train,
+
+            "UPPER CASE" | "UPPER WITH SPACES CASE" => Case::Upper,
+            "lower case" | "lower with spaces case" => Case::Lower,
+            "flatcase" | "lowercase" => Case::Flat,
+            "SCREAMINGFLATCASE" | "UPPERFLATCASE" | "UPPERCASE" => Case::ScreamingFlat,
+
+            _ => return None,
+        }
+        .into()
+    }
+}
+
+pub trait Casing {
+    fn to_case(&self, case: Case) -> String;
+}
+
+impl<T: AsRef<str>> Casing for T {
+    fn to_case(&self, case: Case) -> String {
+        let s = self.as_ref();
+        match case {
+            Case::Pascal => s.to_upper_camel_case(),
+            Case::Camel => s.to_lower_camel_case(),
+            Case::Snake => s.to_snake_case(),
+            Case::Kebab => s.to_kebab_case(),
+            Case::ScreamingSnake => s.to_shouty_snake_case(),
+            Case::Title => s.to_title_case(),
+            Case::Cobol => s.to_shouty_kebab_case(),
+            Case::Train => s.to_train_case(),
+
+            Case::Upper => s.to_shouty_snake_case().replace('_', " "),
+            Case::Lower => s.to_snake_case().replace('_', " "),
+            Case::Flat => s.to_snake_case().replace('_', ""),
+            Case::ScreamingFlat => s.to_shouty_snake_case().replace('_', ""),
+        }
+    }
+}

crates/nu-derive-value/src/from.rs

@@ -1,4 +1,3 @@
-use convert_case::{Case, Casing};
 use proc_macro2::TokenStream as TokenStream2;
 use quote::{quote, ToTokens};
 use syn::{
@@ -6,7 +5,10 @@ use syn::{
     Type,
 };
 
-use crate::attributes::{self, ContainerAttributes};
+use crate::{
+    attributes::{self, ContainerAttributes},
+    case::{Case, Casing},
+};
 
 #[derive(Debug)]
 pub struct FromValue;
@@ -393,7 +395,7 @@ fn derive_enum_from_value(
 /// all possible variants.
 /// The input value is expected to be a `Value::String` containing the name of the variant formatted
 /// as defined by the `#[nu_value(rename_all = "...")]` attribute.
-/// If no attribute is given, [`convert_case::Case::Snake`] is expected.
+/// If no attribute is given, [`snake_case`](heck::ToSnakeCase) is expected.
 ///
 /// If no matching variant is found, `ShellError::CantConvert` is returned.
 ///

crates/nu-derive-value/src/into.rs

@@ -1,4 +1,3 @@
-use convert_case::{Case, Casing};
 use proc_macro2::TokenStream as TokenStream2;
 use quote::{quote, ToTokens};
 use syn::{
@@ -6,7 +5,10 @@ use syn::{
     Index,
 };
 
-use crate::attributes::{self, ContainerAttributes};
+use crate::{
+    attributes::{self, ContainerAttributes},
+    case::{Case, Casing},
+};
 
 #[derive(Debug)]
 pub struct IntoValue;

crates/nu-derive-value/src/lib.rs

@@ -32,6 +32,7 @@ use proc_macro2::TokenStream as TokenStream2;
 use proc_macro_error::{proc_macro_error, Diagnostic};
 
 mod attributes;
+mod case;
 mod error;
 mod from;
 mod into;