Avoid generating and writing bindings when called recursively

from a build script.

src/bindgen/bindings.rs

@@ -27,6 +27,9 @@ pub struct Bindings {
     constants: Vec<Constant>,
     items: Vec<ItemContainer>,
     functions: Vec<Function>,
+    /// Bindings are generated by a recursive call to cbindgen
+    /// and shouldn't do anything when written anywhere.
+    noop: bool,
 }
 
 #[derive(PartialEq)]
@@ -43,6 +46,7 @@ impl Bindings {
         globals: Vec<Static>,
         items: Vec<ItemContainer>,
         functions: Vec<Function>,
+        noop: bool,
     ) -> Bindings {
         Bindings {
             config,
@@ -52,6 +56,7 @@ impl Bindings {
             constants,
             items,
             functions,
+            noop,
         }
     }
 
@@ -93,6 +98,10 @@ impl Bindings {
     }
 
     pub fn write_to_file<P: AsRef<path::Path>>(&self, path: P) -> bool {
+        if self.noop {
+            return false;
+        }
+
         // Don't compare files if we've never written this file before
         if !path.as_ref().is_file() {
             if let Some(parent) = path::Path::new(path.as_ref()).parent() {
@@ -121,6 +130,10 @@ impl Bindings {
     }
 
     pub fn write_headers<F: Write>(&self, out: &mut SourceWriter<F>) {
+        if self.noop {
+            return;
+        }
+
         if let Some(ref f) = self.config.header {
             out.new_line_if_not_start();
             write!(out, "{}", f);
@@ -247,6 +260,10 @@ impl Bindings {
     }
 
     pub fn write<F: Write>(&self, file: F) {
+        if self.noop {
+            return;
+        }
+
         let mut out = SourceWriter::new(file, self);
 
         self.write_headers(&mut out);

src/bindgen/library.rs

@@ -54,6 +54,23 @@ impl Library {
     }
 
     pub fn generate(mut self) -> Result<Bindings, Error> {
+        // If macro expansion is enabled, then cbindgen will attempt to build the crate
+        // and will run its build script which may run cbindgen again. That second run may start
+        // infinite recursion, or overwrite previously written files with bindings.
+        // So if we are called recursively, we are skipping the whole generation
+        // and produce "noop" bindings that won't be able to overwrite anything.
+        if std::env::var("_CBINDGEN_IS_RUNNING").is_ok() {
+            return Ok(Bindings::new(
+                self.config,
+                Default::default(),
+                Default::default(),
+                Default::default(),
+                Default::default(),
+                Default::default(),
+                true,
+            ));
+        }
+
         self.transfer_annotations();
         self.simplify_standard_types();
 
@@ -134,6 +151,7 @@ impl Library {
             globals,
             items,
             functions,
+            false,
         ))
     }
 

src/bindgen/parser.rs

@@ -187,13 +187,6 @@ impl<'a> Parser<'a> {
     fn parse_expand_crate(&mut self, pkg: &PackageRef) -> Result<(), Error> {
         assert!(self.lib.is_some());
 
-        // If you want to expand the crate you run cbindgen on you might end up in an endless
-        // recursion if the cbindgen generation is triggered from build.rs. Hence don't run the
-        // expansion if the build was already triggered by cbindgen.
-        if std::env::var("_CBINDGEN_IS_RUNNING").is_ok() {
-            return Ok(());
-        }
-
         let mod_items = {
             if !self.cache_expanded_crate.contains_key(&pkg.name) {
                 let s = self