Better error messages when procmacro2_semver_exempt is not set

embd-macros/src/lib.rs

@@ -1,16 +1,28 @@
 #![allow(unexpected_cfgs)]
-#![cfg(procmacro2_semver_exempt)]
+#[cfg(procmacro2_semver_exempt)]
 use std::{
     fs,
     path::Path,
 };
 
+#[cfg(not(procmacro2_semver_exempt))]
+compile_error!(
+    r#"pass `--cfg procmacro2_semver_exempt` to rustc to compile embd-macros or add this to your `.cargo/config.toml`:
+
+[build]
+rustflags = [ "--cfg", "procmacro2_semver_exempt" ]
+
+"#
+);
+
+#[cfg(procmacro2_semver_exempt)]
 use proc_macro as pm1;
 use proc_macro2::TokenStream;
 use quote::{
     quote,
     ToTokens,
 };
+#[cfg(procmacro2_semver_exempt)]
 use syn::{
     parse_macro_input,
     spanned::Spanned,
@@ -30,6 +42,7 @@ impl ToTokens for TokenVec {
 }
 
 #[proc_macro]
+#[cfg(procmacro2_semver_exempt)]
 pub fn __dir(input: pm1::TokenStream) -> pm1::TokenStream {
     let input2 = input.clone();
     let path = parse_macro_input!(input2 as LitStr).value();
@@ -52,12 +65,14 @@ pub fn __dir(input: pm1::TokenStream) -> pm1::TokenStream {
     .into()
 }
 
+#[cfg(procmacro2_semver_exempt)]
 fn dir_debug(path: &str) -> TokenStream {
     quote! {
         ::embd::__dir_runtime(file!(), #path)
     }
 }
 
+#[cfg(procmacro2_semver_exempt)]
 fn dir_release(input: TokenStream, path: &str) -> TokenStream {
     let neighbor = TokenStream::from(input).span().source_file().path();
 
@@ -80,6 +95,7 @@ fn dir_release(input: TokenStream, path: &str) -> TokenStream {
     }
 }
 
+#[cfg(procmacro2_semver_exempt)]
 fn read_dir(directory: &Path) -> TokenVec {
     let mut entries = Vec::new();
 

embd/src/lib.rs

@@ -1,11 +1,20 @@
 #![allow(unexpected_cfgs)]
-#![cfg(procmacro2_semver_exempt)]
 use std::{
     borrow::Cow,
     fs,
     path::Path,
 };
 
+#[cfg(not(procmacro2_semver_exempt))]
+compile_error!(
+    r#"pass `--cfg procmacro2_semver_exempt` to rustc to compile embd or add this to your `.cargo/config.toml`:
+
+[build]
+rustflags = [ "--cfg", "procmacro2_semver_exempt" ]
+
+"#
+);
+
 #[doc(hidden)]
 pub fn __string_runtime(neighbor: &str, path: &str) -> String {
     let file = Path::new(neighbor)
@@ -27,6 +36,7 @@ pub fn __string_runtime(neighbor: &str, path: &str) -> String {
 /// }
 /// ```
 #[macro_export]
+#[cfg(procmacro2_semver_exempt)]
 macro_rules! string {
     ($path:literal) => {{
         #[cfg(debug_assertions)]
@@ -62,6 +72,7 @@ pub fn __bytes_runtime(neighbor: &str, path: &str) -> Vec<u8> {
 /// }
 /// ```
 #[macro_export]
+#[cfg(procmacro2_semver_exempt)]
 macro_rules! bytes {
     ($path:literal) => {{
         #[cfg(debug_assertions)]
@@ -223,4 +234,5 @@ pub fn __dir_runtime(neighbor: &str, path: &str) -> Dir {
 ///     let content: embd::Dir = embd::dir!("../assets");
 /// }
 /// ```
+#[cfg(procmacro2_semver_exempt)]
 pub use embd_macros::__dir as dir;