macro: support env vars in package attributes

Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>

perlmod-macro/src/attribs.rs

@@ -26,11 +26,11 @@ impl TryFrom<AttributeArgs> for ModuleAttrs {
                     ..
                 })) => {
                     if path.is_ident("name") {
-                        package_name = Some(litstr.value());
+                        package_name = Some(expand_env_vars(&litstr)?);
                     } else if path.is_ident("file") {
-                        file_name = Some(litstr.value());
+                        file_name = Some(expand_env_vars(&litstr)?);
                     } else if path.is_ident("lib") {
-                        lib_name = Some(litstr.value());
+                        lib_name = Some(expand_env_vars(&litstr)?);
                     } else {
                         bail!(path => "unknown argument");
                     }
@@ -50,6 +50,39 @@ impl TryFrom<AttributeArgs> for ModuleAttrs {
     }
 }
 
+fn expand_env_vars(lit_str: &syn::LitStr) -> Result<String, syn::Error> {
+    let input = lit_str.value();
+    let mut expanded = String::with_capacity(input.len());
+
+    let mut input = input.as_str();
+    loop {
+        let dollar = match input.find("${") {
+            Some(d) => d,
+            None => {
+                expanded.push_str(input);
+                break;
+            }
+        };
+
+        expanded.push_str(&input[..dollar]);
+        input = &input[(dollar + 2)..];
+
+        let end = input.find('}').ok_or_else(
+            || format_err!(lit_str => "missing end of environment variable expansion"),
+        )?;
+
+        let var_name = &input[..end];
+        input = &input[(end + 1)..];
+
+        let var = std::env::var(var_name).map_err(|err| {
+            format_err!(lit_str => "failed to expand environment variable {:?}: {}", var_name, err)
+        })?;
+        expanded.push_str(&var);
+    }
+
+    Ok(expanded)
+}
+
 impl ModuleAttrs {
     pub fn mangle_package_name(&self) -> String {
         let mut out = String::with_capacity(self.package_name.len());

perlmod-macro/src/lib.rs

@@ -51,6 +51,8 @@ fn handle_error(mut item: TokenStream, data: Result<TokenStream, Error>) -> Toke
 /// ```
 /// // 'lib' and 'file' are optional. We use 'file' here to prevent doc tests from writing out the
 /// // file.
+/// //
+/// // 'name', 'lib' and 'file' expand environment variables such as `${CARGO_PKG_NAME}`
 /// #[perlmod::package(name = "RSPM::Foo", lib = "perlmod_test", file = "/dev/null")]
 /// mod an_unused_name {
 ///     use anyhow::{bail, Error};

perlmod-test/src/pkg142.rs

@@ -34,3 +34,14 @@ mod export {
         Ok(value.0)
     }
 }
+
+#[perlmod::package(name = "RSPM::EnvVarLibrary", lib = "x-${CARGO_PKG_NAME}-y")]
+mod expanded_export {
+    use anyhow::Error;
+
+    #[export]
+    fn test_lib_env_vars(value: &str) -> Result<(), Error> {
+        println!("foo: {:?}", value);
+        Ok(())
+    }
+}