Add dynamic loading support

Closes #1541.
Closes #1846.

Co-authored-by: Michael-F-Bryan <michaelfbryan@gmail.com>

src/codegen/dyngen.rs

@@ -0,0 +1,181 @@
+use crate::ir::function::Abi;
+use proc_macro2::Ident;
+
+/// Used to build the output tokens for dynamic bindings.
+pub struct DynamicItems {
+    /// Tracks the tokens that will appears inside the library struct -- e.g.:
+    /// ```ignore
+    /// struct Lib {
+    ///    __library: ::libloading::Library,
+    ///    x: Result<unsafe extern ..., ::libloading::Error>, // <- tracks these
+    ///    ...
+    /// }
+    /// ```
+    struct_members: Vec<proc_macro2::TokenStream>,
+
+    /// Tracks the tokens that will appear inside the library struct's implementation, e.g.:
+    ///
+    /// ```ignore
+    /// impl Lib {
+    ///     ...
+    ///     pub unsafe fn foo(&self, ...) { // <- tracks these
+    ///         ...
+    ///     }
+    /// }
+    /// ```
+    struct_implementation: Vec<proc_macro2::TokenStream>,
+
+    /// Tracks the tokens that will appear inside the struct used for checking if a symbol is
+    /// usable, e.g.:
+    /// ```ignore
+    /// pub fn f(&self) -> Result<(), &'a ::libloading::Error> { // <- tracks these
+    ///     self.__library.f.as_ref().map(|_| ())
+    /// }
+    /// ```
+    runtime_checks: Vec<proc_macro2::TokenStream>,
+
+    /// Tracks the initialization of the fields inside the `::new` constructor of the library
+    /// struct, e.g.:
+    /// ```ignore
+    /// impl Lib {
+    ///
+    ///     pub unsafe fn new<P>(path: P) -> Result<Self, ::libloading::Error>
+    ///     where
+    ///         P: AsRef<::std::ffi::OsStr>,
+    ///     {
+    ///         ...
+    ///         let foo = __library.get(...) ...; // <- tracks these
+    ///         ...
+    ///     }
+    ///
+    ///     ...
+    /// }
+    /// ```
+    constructor_inits: Vec<proc_macro2::TokenStream>,
+
+    /// Tracks the information that is passed to the library struct at the end of the `::new`
+    /// constructor, e.g.:
+    /// ```ignore
+    /// impl LibFoo {
+    ///     pub unsafe fn new<P>(path: P) -> Result<Self, ::libloading::Error>
+    ///     where
+    ///         P: AsRef<::std::ffi::OsStr>,
+    ///     {
+    ///         ...
+    ///         Ok(LibFoo {
+    ///             __library: __library,
+    ///             foo,
+    ///             bar, // <- tracks these
+    ///             ...
+    ///         })
+    ///     }
+    /// }
+    /// ```
+    init_fields: Vec<proc_macro2::TokenStream>,
+}
+
+impl Default for DynamicItems {
+    fn default() -> Self {
+        DynamicItems {
+            struct_members: vec![],
+            struct_implementation: vec![],
+            runtime_checks: vec![],
+            constructor_inits: vec![],
+            init_fields: vec![],
+        }
+    }
+}
+
+impl DynamicItems {
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    pub fn get_tokens(
+        &self,
+        lib_ident: Ident,
+        check_struct_ident: Ident,
+    ) -> proc_macro2::TokenStream {
+        let struct_members = &self.struct_members;
+        let constructor_inits = &self.constructor_inits;
+        let init_fields = &self.init_fields;
+        let struct_implementation = &self.struct_implementation;
+        let runtime_checks = &self.runtime_checks;
+        quote! {
+            extern crate libloading;
+
+            pub struct #lib_ident {
+                __library: ::libloading::Library,
+                #(#struct_members)*
+            }
+
+            impl #lib_ident {
+                pub unsafe fn new<P>(
+                    path: P
+                ) -> Result<Self, ::libloading::Error>
+                where P: AsRef<::std::ffi::OsStr> {
+                    let __library = ::libloading::Library::new(path)?;
+                    #( #constructor_inits )*
+                    Ok(
+                        #lib_ident {
+                            __library: __library,
+                            #( #init_fields ),*
+                        }
+                    )
+                }
+
+                pub fn can_call(&self) -> #check_struct_ident {
+                    #check_struct_ident { __library: self }
+                }
+
+                #( #struct_implementation )*
+            }
+
+            pub struct #check_struct_ident<'a> {
+                __library: &'a #lib_ident,
+            }
+
+            impl<'a> #check_struct_ident<'a> {
+                #( #runtime_checks )*
+            }
+        }
+    }
+
+    pub fn add_function(
+        &mut self,
+        ident: Ident,
+        abi: Abi,
+        args: Vec<proc_macro2::TokenStream>,
+        args_identifiers: Vec<proc_macro2::TokenStream>,
+        ret: proc_macro2::TokenStream,
+        ret_ty: proc_macro2::TokenStream,
+    ) {
+        assert_eq!(args.len(), args_identifiers.len());
+
+        self.struct_members.push(quote!{
+            #ident: Result<unsafe extern #abi fn ( #( #args ),* ) #ret, ::libloading::Error>,
+        });
+
+        self.struct_implementation.push(quote! {
+            pub unsafe fn #ident ( &self, #( #args ),* ) -> #ret_ty {
+                let sym = self.#ident.as_ref().expect("Expected function, got error.");
+                (sym)(#( #args_identifiers ),*)
+            }
+        });
+
+        self.runtime_checks.push(quote! {
+            pub fn #ident (&self) -> Result<(), &'a::libloading::Error> {
+                self.__library.#ident.as_ref().map(|_| ())
+            }
+        });
+
+        let ident_str = ident.to_string();
+        self.constructor_inits.push(quote! {
+            let #ident = __library.get(#ident_str.as_bytes()).map(|sym| *sym);
+        });
+
+        self.init_fields.push(quote! {
+            #ident
+        });
+    }
+}

src/codegen/mod.rs

@@ -1,3 +1,4 @@
+mod dyngen;
 mod error;
 mod helpers;
 mod impl_debug;
@@ -10,6 +11,7 @@ pub(crate) mod bitfield_unit;
 #[cfg(all(test, target_endian = "little"))]
 mod bitfield_unit_tests;
 
+use self::dyngen::DynamicItems;
 use self::helpers::attributes;
 use self::struct_layout::StructLayoutTracker;
 
@@ -184,6 +186,7 @@ impl From<DerivableTraits> for Vec<&'static str> {
 
 struct CodegenResult<'a> {
     items: Vec<proc_macro2::TokenStream>,
+    dynamic_items: DynamicItems,
 
     /// A monotonic counter used to add stable unique id's to stuff that doesn't
     /// need to be referenced by anything.
@@ -234,6 +237,7 @@ impl<'a> CodegenResult<'a> {
     fn new(codegen_id: &'a Cell<usize>) -> Self {
         CodegenResult {
             items: vec![],
+            dynamic_items: DynamicItems::new(),
             saw_bindgen_union: false,
             saw_incomplete_array: false,
             saw_objc: false,
@@ -247,6 +251,10 @@ impl<'a> CodegenResult<'a> {
         }
     }
 
+    fn dynamic_items(&mut self) -> &mut DynamicItems {
+        &mut self.dynamic_items
+    }
+
     fn saw_bindgen_union(&mut self) {
         self.saw_bindgen_union = true;
     }
@@ -3785,7 +3793,29 @@ impl CodeGenerator for Function {
                 pub fn #ident ( #( #args ),* ) #ret;
             }
         };
-        result.push(tokens);
+
+        // If we're doing dynamic binding generation, add to the dynamic items.
+        if ctx.options().dynamic_library_name.is_some() &&
+            self.kind() == FunctionKind::Function
+        {
+            let args_identifiers =
+                utils::fnsig_argument_identifiers(ctx, signature);
+            let return_item = ctx.resolve_item(signature.return_type());
+            let ret_ty = match *return_item.kind().expect_type().kind() {
+                TypeKind::Void => quote! {()},
+                _ => return_item.to_rust_ty_or_opaque(ctx, &()),
+            };
+            result.dynamic_items().add_function(
+                ident,
+                abi,
+                args,
+                args_identifiers,
+                ret,
+                ret_ty,
+            );
+        } else {
+            result.push(tokens);
+        }
     }
 }
 
@@ -4075,11 +4105,28 @@ pub(crate) fn codegen(
             &(),
         );
 
+        if context.options().dynamic_library_name.is_some() {
+            let lib_ident = context.rust_ident(
+                context.options().dynamic_library_name.as_ref().unwrap(),
+            );
+            let check_struct_ident = context.rust_ident(
+                [
+                    "Check",
+                    context.options().dynamic_library_name.as_ref().unwrap(),
+                ]
+                .join(""),
+            );
+            let dynamic_items_tokens = result
+                .dynamic_items()
+                .get_tokens(lib_ident, check_struct_ident);
+            result.push(dynamic_items_tokens);
+        }
+
         result.items
     })
 }
 
-mod utils {
+pub mod utils {
     use super::{error, ToRustTyOrOpaque};
     use crate::ir::context::BindgenContext;
     use crate::ir::function::{Abi, FunctionSig};
@@ -4484,6 +4531,35 @@ mod utils {
         args
     }
 
+    pub fn fnsig_argument_identifiers(
+        ctx: &BindgenContext,
+        sig: &FunctionSig,
+    ) -> Vec<proc_macro2::TokenStream> {
+        let mut unnamed_arguments = 0;
+        let args = sig
+            .argument_types()
+            .iter()
+            .map(|&(ref name, _ty)| {
+                let arg_name = match *name {
+                    Some(ref name) => ctx.rust_mangle(name).into_owned(),
+                    None => {
+                        unnamed_arguments += 1;
+                        format!("arg{}", unnamed_arguments)
+                    }
+                };
+
+                assert!(!arg_name.is_empty());
+                let arg_name = ctx.rust_ident(arg_name);
+
+                quote! {
+                    #arg_name
+                }
+            })
+            .collect::<Vec<_>>();
+
+        args
+    }
+
     pub fn fnsig_block(
         ctx: &BindgenContext,
         sig: &FunctionSig,

src/lib.rs

@@ -518,6 +518,12 @@ impl Builder {
             output_vector.push(path.into());
         }
 
+        if self.options.dynamic_library_name.is_some() {
+            let libname = self.options.dynamic_library_name.as_ref().unwrap();
+            output_vector.push("--dynamic-loading".into());
+            output_vector.push(libname.clone());
+        }
+
         // Add clang arguments
 
         output_vector.push("--".into());
@@ -1468,6 +1474,15 @@ impl Builder {
         self.options.wasm_import_module_name = Some(import_name.into());
         self
     }
+
+    /// Specify the dynamic library name if we are generating bindings for a shared library.
+    pub fn dynamic_library_name<T: Into<String>>(
+        mut self,
+        dynamic_library_name: T,
+    ) -> Self {
+        self.options.dynamic_library_name = Some(dynamic_library_name.into());
+        self
+    }
 }
 
 /// Configuration options for generated bindings.
@@ -1745,6 +1760,10 @@ struct BindgenOptions {
 
     /// Wasm import module name.
     wasm_import_module_name: Option<String>,
+
+    /// The name of the dynamic library (if we are generating bindings for a shared library). If
+    /// this is None, no dynamic bindings are created.
+    dynamic_library_name: Option<String>,
 }
 
 /// TODO(emilio): This is sort of a lie (see the error message that results from
@@ -1877,6 +1896,7 @@ impl Default for BindgenOptions {
             no_hash_types: Default::default(),
             array_pointers_in_arguments: false,
             wasm_import_module_name: None,
+            dynamic_library_name: None,
         }
     }
 }

src/options.rs

@@ -471,7 +471,11 @@ where
                 .long("wasm-import-module-name")
                 .value_name("name")
                 .takes_value(true)
-                .help("The name to be used in a #[link(wasm_import_module = ...)] statement")
+                .help("The name to be used in a #[link(wasm_import_module = ...)] statement"),
+            Arg::with_name("dynamic-loading")
+                .long("dynamic-loading")
+                .takes_value(true)
+                .help("Use dynamic loading mode with the given library name."),
         ]) // .args()
         .get_matches_from(args);
 
@@ -873,6 +877,10 @@ where
         }
     }
 
+    if let Some(dynamic_library_name) = matches.value_of("dynamic-loading") {
+        builder = builder.dynamic_library_name(dynamic_library_name);
+    }
+
     let verbose = matches.is_present("verbose");
 
     Ok((builder, output, verbose))