Change name when outputting staticlibs on Windows

libfoo.a -> foo.lib
In order to not cause conflicts, changes the DLL import library name
foo.lib -> foo.dll.lib

Fixes https://github.com/rust-lang/rust/issues/29508

Because this changes output filenames this is a [breaking-change]

Signed-off-by: Peter Atashian <retep998@gmail.com>

src/librustc_metadata/loader.rs

@@ -388,11 +388,12 @@ impl<'a> Context<'a> {
         }
 
         let dypair = self.dylibname();
+        let staticpair = self.staticlibname();
 
         // want: crate_name.dir_part() + prefix + crate_name.file_part + "-"
         let dylib_prefix = format!("{}{}", dypair.0, self.crate_name);
         let rlib_prefix = format!("lib{}", self.crate_name);
-        let staticlib_prefix = format!("lib{}", self.crate_name);
+        let staticlib_prefix = format!("{}{}", staticpair.0, self.crate_name);
 
         let mut candidates = HashMap::new();
         let mut staticlibs = vec!();
@@ -425,7 +426,7 @@ impl<'a> Context<'a> {
                  false)
             } else {
                 if file.starts_with(&staticlib_prefix[..]) &&
-                   file.ends_with(".a") {
+                   file.ends_with(&staticpair.1) {
                     staticlibs.push(CrateMismatch {
                         path: path.to_path_buf(),
                         got: "static".to_string()
@@ -644,6 +645,13 @@ impl<'a> Context<'a> {
         (t.options.dll_prefix.clone(), t.options.dll_suffix.clone())
     }
 
+    // Returns the corresponding (prefix, suffix) that files need to have for
+    // static libraries
+    fn staticlibname(&self) -> (String, String) {
+        let t = &self.target;
+        (t.options.staticlib_prefix.clone(), t.options.staticlib_suffix.clone())
+    }
+
     fn find_commandline_library(&mut self, locs: &[String]) -> Option<Library> {
         // First, filter out all libraries that look suspicious. We only accept
         // files which actually exist that have the correct naming scheme for

src/librustc_trans/back/link.rs

@@ -490,7 +490,10 @@ pub fn filename_for_input(sess: &Session,
                                                 suffix))
         }
         config::CrateTypeStaticlib => {
-            outputs.out_directory.join(&format!("lib{}.a", libname))
+            let (prefix, suffix) = (&sess.target.target.options.staticlib_prefix,
+                                    &sess.target.target.options.staticlib_suffix);
+            outputs.out_directory.join(&format!("{}{}{}", prefix, libname,
+                                                suffix))
         }
         config::CrateTypeExecutable => {
             let suffix = &sess.target.target.options.exe_suffix;

src/librustc_trans/back/linker.rs

@@ -210,7 +210,14 @@ impl<'a> Linker for MsvcLinker<'a> {
     fn link_rlib(&mut self, lib: &Path) { self.cmd.arg(lib); }
     fn add_object(&mut self, path: &Path) { self.cmd.arg(path); }
     fn args(&mut self, args: &[String]) { self.cmd.args(args); }
-    fn build_dylib(&mut self, _out_filename: &Path) { self.cmd.arg("/DLL"); }
+
+    fn build_dylib(&mut self, out_filename: &Path) {
+        self.cmd.arg("/DLL");
+        let mut arg: OsString = "/IMPLIB:".into();
+        arg.push(out_filename.with_extension("dll.lib"));
+        self.cmd.arg(arg);
+    }
+
     fn gc_sections(&mut self, _is_dylib: bool) { self.cmd.arg("/OPT:REF,ICF"); }
 
     fn link_dylib(&mut self, lib: &str) {
@@ -222,7 +229,7 @@ impl<'a> Linker for MsvcLinker<'a> {
         // `foo.lib` file if the dll doesn't actually export any symbols, so we
         // check to see if the file is there and just omit linking to it if it's
         // not present.
-        let name = format!("{}.lib", lib);
+        let name = format!("{}.dll.lib", lib);
         if fs::metadata(&path.join(&name)).is_ok() {
             self.cmd.arg(name);
         }