store warnings and emit them later

3 files changed, 45 insertions, 7 deletions

diff --git a/src/codegen/mod.rs b/src/codegen/mod.rs
index 6bbb7ab5..77e9ba95 100644
--- a/src/codegen/mod.rs
+++ b/src/codegen/mod.rs
@@ -4329,7 +4329,7 @@ impl CodeGenerator for ObjCInterface {
 
 pub(crate) fn codegen(
     context: BindgenContext,
-) -> (Vec<proc_macro2::TokenStream>, BindgenOptions) {
+) -> (Vec<proc_macro2::TokenStream>, BindgenOptions, Vec<String>) {
     context.gen(|context| {
         let _t = context.timer("codegen");
         let counter = Cell::new(0);
diff --git a/src/ir/context.rs b/src/ir/context.rs
index 36d7eedb..61fa8439 100644
--- a/src/ir/context.rs
+++ b/src/ir/context.rs
@@ -459,6 +459,9 @@ pub struct BindgenContext {
     /// Populated when we enter codegen by `compute_has_float`; always `None`
     /// before that and `Some` after.
     has_float: Option<HashSet<ItemId>>,
+
+    /// The set of warnings raised during binding generation.
+    warnings: Vec<String>,
 }
 
 /// A traversal of allowlisted items.
@@ -579,6 +582,7 @@ If you encounter an error missing from this list, please file an issue or a PR!"
             have_destructor: None,
             has_type_param_in_array: None,
             has_float: None,
+            warnings: Vec::new(),
         }
     }
 
@@ -1134,7 +1138,10 @@ If you encounter an error missing from this list, please file an issue or a PR!"
 
     /// Enter the code generation phase, invoke the given callback `cb`, and
     /// leave the code generation phase.
-    pub(crate) fn gen<F, Out>(mut self, cb: F) -> (Out, BindgenOptions)
+    pub(crate) fn gen<F, Out>(
+        mut self,
+        cb: F,
+    ) -> (Out, BindgenOptions, Vec<String>)
     where
         F: FnOnce(&Self) -> Out,
     {
@@ -1171,7 +1178,7 @@ If you encounter an error missing from this list, please file an issue or a PR!"
         self.compute_cannot_derive_partialord_partialeq_or_eq();
 
         let ret = cb(&self);
-        (ret, self.options)
+        (ret, self.options, self.warnings)
     }
 
     /// When the `testing_only_extra_assertions` feature is enabled, this
@@ -2430,17 +2437,27 @@ If you encounter an error missing from this list, please file an issue or a PR!"
         self.allowlisted = Some(allowlisted);
         self.codegen_items = Some(codegen_items);
 
+        let mut warnings = Vec::new();
+
         for item in self.options().allowlisted_functions.unmatched_items() {
-            warn!("unused option: --allowlist-function {}", item);
+            let warn = format!("unused option: --allowlist-function {}", item);
+            warn!("{}", warn);
+            warnings.push(warn);
         }
 
         for item in self.options().allowlisted_vars.unmatched_items() {
-            warn!("unused option: --allowlist-var {}", item);
+            let warn = format!("unused option: --allowlist-var {}", item);
+            warn!("{}", warn);
+            warnings.push(warn);
         }
 
         for item in self.options().allowlisted_types.unmatched_items() {
-            warn!("unused option: --allowlist-type {}", item);
+            let warn = format!("unused option: --allowlist-type {}", item);
+            warn!("{}", warn);
+            warnings.push(warn);
         }
+
+        self.warnings.extend(warnings);
     }
 
     /// Convenient method for getting the prefix to use for most traits in
diff --git a/src/lib.rs b/src/lib.rs
index 3d09ab71..cbcf65e3 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -33,6 +33,19 @@ mod log_stubs;
 #[macro_use]
 mod extra_assertions;
 
+/// Print all the warning messages raised while generating the bindings in a build script.
+///
+/// If you are using `bindgen` outside of a build script you should use [`Bindings::take_warnings`]
+/// directly instead.
+#[macro_export]
+macro_rules! print_warnings {
+    ($bindings:expr) => {
+        for message in $bindings.take_warnings() {
+            println!("cargo:warning={}", message);
+        }
+    };
+}
+
 // A macro to declare an internal module for which we *must* provide
 // documentation for. If we are building with the "testing_only_docs" feature,
 // then the module is declared public, and our `#![deny(missing_docs)]` pragma
@@ -2222,6 +2235,7 @@ impl std::error::Error for BindgenError {}
 #[derive(Debug)]
 pub struct Bindings {
     options: BindgenOptions,
+    warnings: Vec<String>,
     module: proc_macro2::TokenStream,
 }
 
@@ -2435,10 +2449,11 @@ impl Bindings {
             parse(&mut context)?;
         }
 
-        let (items, options) = codegen::codegen(context);
+        let (items, options, warnings) = codegen::codegen(context);
 
         Ok(Bindings {
             options,
+            warnings,
             module: quote! {
                 #( #items )*
             },
@@ -2583,6 +2598,12 @@ impl Bindings {
             _ => Ok(Cow::Owned(source)),
         }
     }
+
+    /// Take all the warning messages.
+    #[inline]
+    pub fn take_warnings(&mut self) -> impl Iterator<Item = String> + '_ {
+        self.warnings.drain(..)
+    }
 }
 
 impl std::fmt::Display for Bindings {