support camel modifier for snake to camel case

impl/src/lib.rs

@@ -194,6 +194,26 @@ fn paste_segments(span: Span, segments: &[Segment]) -> Result<TokenStream> {
                         prev = ch;
                     }
                     evaluated.push(acc.to_lowercase());
+                } else if ident == "camel" {
+                    let mut acc = String::new();
+                    let mut prev = '_';
+                    for ch in last.chars() {
+                        if ch != '_' {
+                            if prev == '_' {
+                                for chu in ch.to_uppercase() {
+                                    acc.push(chu);
+                                }
+                            } else if prev.is_uppercase() {
+                                for chl in ch.to_lowercase() {
+                                    acc.push(chl);
+                                }
+                            } else {
+                                acc.push(ch);
+                            }
+                        }
+                        prev = ch;
+                    }
+                    evaluated.push(acc);
                 } else {
                     return Err(Error::new_spanned(span, "unsupported modifier"));
                 }

src/lib.rs

@@ -117,8 +117,9 @@
 //! example, `[<ld_ $reg:lower _expr>]` would paste to `ld_bc_expr` if invoked
 //! with $reg=`Bc`.
 //!
-//! Use `$var:snake` to convert CamelCase input to snake\_case. These compose,
-//! so for example `$var:snake:upper` would give you SCREAMING\_CASE.
+//! Use `$var:snake` to convert CamelCase input to snake\_case.
+//! Use `$var:camel` to convert snake\_case to CamelCase.
+//! These compose, so for example `$var:snake:upper` would give you SCREAMING\_CASE.
 //!
 //! The precise Unicode conversions are as defined by [`str::to_lowercase`] and
 //! [`str::to_uppercase`].

tests/test.rs

@@ -255,3 +255,33 @@ fn test_env_to_snake() {
         let _ = LIBPASTE;
     }
 }
+
+mod test_to_camel {
+    macro_rules! m {
+        ($id:ident) => {
+            paste::item! {
+                const DEFAULT_CAMEL: &str = stringify!([<$id:camel>]);
+                const LOWER_CAMEL: &str = stringify!([<$id:camel:lower>]);
+                const UPPER_CAMEL: &str = stringify!([<$id:camel:upper>]);
+            }
+        };
+    }
+
+    m!(this_is_but_a_test);
+
+    #[test]
+    fn test_to_snake() {
+        assert_eq!(DEFAULT_CAMEL, "ThisIsButATest");
+        assert_eq!(LOWER_CAMEL, "thisisbutatest");
+        assert_eq!(UPPER_CAMEL, "THISISBUTATEST");
+    }
+}
+
+#[test]
+fn test_env_to_camel() {
+    paste::expr! {
+        const [<LIB env!("CARGO_PKG_NAME"):camel>]: &str = "libpaste";
+
+        let _ = LIBPaste;
+    }
+}