Escape spaces in the depfile output

CHANGELOG.md

@@ -177,6 +177,10 @@
   statement and only call the static function instead.
 * The `--wrap-static-fns` option no longer emits wrappers for static variadic
   functions.
+* Depfiles generated with `--depfile` or `Builder::depfile` will now be
+  properly generate module names and paths that include spaces by escaping
+  them. To make the escaping clear and consistent, backslashes are also
+  escaped.
 
 ## Removed
 

bindgen/deps.rs

@@ -9,12 +9,53 @@ pub(crate) struct DepfileSpec {
 
 impl DepfileSpec {
     pub fn write(&self, deps: &BTreeSet<String>) -> std::io::Result<()> {
-        let mut buf = format!("{}:", self.output_module);
+        std::fs::write(&self.depfile_path, &self.to_string(deps))
+    }
+
+    fn to_string(&self, deps: &BTreeSet<String>) -> String {
+        // Transforms a string by escaping spaces and backslashes.
+        let escape = |s: &str| s.replace('\\', "\\\\").replace(' ', "\\ ");
 
+        let mut buf = format!("{}:", escape(&self.output_module));
         for file in deps {
-            buf = format!("{} {}", buf, file);
+            buf = format!("{} {}", buf, escape(file));
         }
+        buf
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn escaping_depfile() {
+        let spec = DepfileSpec {
+            output_module: "Mod Name".to_owned(),
+            depfile_path: PathBuf::new(),
+        };
 
-        std::fs::write(&self.depfile_path, &buf)
+        let deps: BTreeSet<String> = vec![
+            r"/absolute/path".to_owned(),
+            r"C:\win\absolute\path".to_owned(),
+            r"../relative/path".to_owned(),
+            r"..\win\relative\path".to_owned(),
+            r"../path/with spaces/in/it".to_owned(),
+            r"..\win\path\with spaces\in\it".to_owned(),
+            r"path\with/mixed\separators".to_owned(),
+        ]
+        .into_iter()
+        .collect();
+        assert_eq!(
+            spec.to_string(&deps),
+            "Mod\\ Name: \
+            ../path/with\\ spaces/in/it \
+            ../relative/path \
+            ..\\\\win\\\\path\\\\with\\ spaces\\\\in\\\\it \
+            ..\\\\win\\\\relative\\\\path \
+            /absolute/path \
+            C:\\\\win\\\\absolute\\\\path \
+            path\\\\with/mixed\\\\separators"
+        );
     }
 }