tb: fix case check logic

This commit fixes an issue with `convert_case` crate reported in [1].

The issue is that the default implementation of `is_case` provided by
that crate initializes the converter with almost all available
boundaries.

As a result the following conversion takes place:

"ERR1".to_case(Case::UpperSnake) -> "ERR_1"

Furthermore, the following check fails, while it seems like it
shouldn't because the string is in capital letters.

"ERR1".is_case(Case::UpperSnake)

This commit introduces a new primitive `convert_case` which receives two
case parameters, one for the source case and one of the target case.
This way the converter is initialized with the correct source case
boundaries. And it allows implementation of a new `is_case` primitive
that builds on `convert_case` to select the source case boundaries
correctly.

[1] rutrum/convert-case#21

crates/tighterror-build/src/parser/helpers.rs

@@ -3,7 +3,7 @@ use crate::{
     errors::{kinds::parser::*, TbError},
     parser::kws,
 };
-use convert_case::{Case, Casing};
+use convert_case::Case;
 use regex::Regex;
 use std::collections::HashSet;
 
@@ -19,6 +19,17 @@ pub fn check_ident_chars(ident: &str, desc: &str) -> Result<(), TbError> {
     }
 }
 
+fn convert_case(s: &str, from_case: Case, to_case: Case) -> String {
+    let converter = convert_case::Converter::new()
+        .from_case(from_case)
+        .to_case(to_case);
+    converter.convert(s)
+}
+
+fn is_case(s: &str, case: Case) -> bool {
+    convert_case(s, case, case) == s
+}
+
 fn check_ident(ident: &str, desc: &str, case: Case) -> Result<(), TbError> {
     if ident.is_empty() {
         log::error!("`{desc}` cannot be an empty string");
@@ -27,10 +38,10 @@ fn check_ident(ident: &str, desc: &str, case: Case) -> Result<(), TbError> {
 
     check_ident_chars(ident, desc)?;
 
-    if !ident.is_case(case) {
+    if !is_case(ident, case) {
         log::error!(
             "`{desc}` must be specified in {case:?} case: {ident} -> {}",
-            ident.to_case(case)
+            convert_case(ident, case, case)
         );
         return BAD_IDENTIFIER_CASE.into();
     }
@@ -84,7 +95,7 @@ pub fn check_module_name(name: &str) -> Result<(), TbError> {
     if name.is_empty() {
         log::error!("module name cannot be an empty string");
         BAD_NAME.into()
-    } else if !name.is_case(Case::Snake) {
+    } else if !is_case(name, Case::Snake) {
         log::error!("module name must be specified in lower_snake_case: {name}");
         BAD_NAME.into()
     } else {
@@ -152,3 +163,24 @@ where
 {
     check_name_uniqueness("module", iter)
 }
+
+#[cfg(test)]
+mod testing {
+    use super::*;
+    use convert_case::Case::*;
+
+    #[test]
+    fn test_convert_case() {
+        let cases = &[
+            // str_to_convert, from_case, to_case, expected_result
+            ("MY_ERR1", UpperSnake, UpperSnake, "MY_ERR1"),
+            ("MyErr1", UpperSnake, UpperSnake, "MYERR1"),
+            ("MyErr1", UpperCamel, UpperSnake, "MY_ERR_1"),
+            ("MY_ERR1", UpperSnake, UpperCamel, "MyErr1"),
+        ];
+
+        for c in cases {
+            assert_eq!(convert_case(c.0, c.1, c.2), c.3);
+        }
+    }
+}