Pretty-print the generated bindings

Per default, bindgen puts everything onto one line.
This pretty printer will insert newlines for better readability.

See rust-lang/rust-bindgen#1600

Author: est31

Cargo.lock

@@ -14,3 +14,4 @@ include = ["deepspeech/native_client/deepspeech.h", "/src/**",
 
 [build-dependencies]
 bindgen = { version = "0.51", default-features = false }
+proc-macro2 = { version = "0.4", default-features = false }

sys/Cargo.toml

@@ -1,7 +1,68 @@
 extern crate bindgen;
+extern crate proc_macro2;
 
 use std::env;
 use std::path::PathBuf;
+use std::path::Path;
+
+fn write_to_file(path: impl AsRef<Path>, bindings: &bindgen::Bindings) {
+    use proc_macro2::{TokenStream, TokenTree, Spacing, Delimiter};
+    use std::str::FromStr;
+    let str_bindings = bindings.to_string();
+    let tokens = TokenStream::from_str(&str_bindings).unwrap();
+    let mut res_str = String::new();
+    struct TokenVisitor<'s> {
+        s: &'s mut String,
+    }
+    impl<'s> TokenVisitor<'s> {
+        fn visit_stream(&mut self, stream: TokenStream) {
+            let mut iter = stream.into_iter().peekable();
+            while let Some(tree) = iter.next() {
+                self.visit_tree(tree, iter.peek().is_some());
+            }
+        }
+        fn visit_tree(&mut self, tree: TokenTree, put_space: bool) {
+            let mut put_space = put_space;
+            match tree {
+                TokenTree::Group(group) => {
+                    match group.delimiter() {
+                        Delimiter::Brace => {
+                            *self.s += "{\n";
+                            self.visit_stream(group.stream());
+                            *self.s += "\n}\n";
+                        },
+                        _ => *self.s += &group.to_string(),
+                    }
+                },
+                TokenTree::Ident(ident) => {
+                    *self.s += &ident.to_string();
+                },
+                TokenTree::Punct(punct) => {
+                    if punct.spacing() == Spacing::Alone && punct.as_char() == ';' {
+                        *self.s += &punct.to_string();
+                        *self.s += "\n";
+                    } else {
+                        *self.s += &punct.to_string();
+                    }
+                    if punct.spacing() == Spacing::Joint {
+                        put_space = false;
+                    }
+                },
+                TokenTree::Literal(l) => {
+                    *self.s += &l.to_string();
+                },
+            }
+            if put_space {
+                *self.s += " ";
+            }
+        }
+    }
+    let mut visitor = TokenVisitor {
+        s: &mut res_str
+    };
+    visitor.visit_stream(tokens);
+    std::fs::write(path, visitor.s.as_bytes()).unwrap();
+}
 
 fn main() {
 	println!("cargo:rustc-link-lib=deepspeech");
@@ -14,6 +75,5 @@ fn main() {
 		.expect("Couldn't generate bindings");
 
 	let out_path = PathBuf::from(env::var("OUT_DIR").unwrap());
-	bindings.write_to_file(out_path.join("bindings.rs"))
-		.expect("Couldn't write bindings!");
+	write_to_file(out_path.join("bindings.rs"), &bindings);
 }