Auto merge of #5171 - rtsuk:gn-compatible-depfiles, r=alexcrichton

Gn compatible depfiles

Fixes https://github.com/rust-lang/cargo/issues/5162.

src/cargo/ops/cargo_rustc/output_depinfo.rs

@@ -70,7 +70,15 @@ pub fn output_depinfo<'a, 'b>(context: &mut Context<'a, 'b>, unit: &Unit<'a>) ->
     let mut deps = HashSet::new();
     let mut visited = HashSet::new();
     let success = add_deps_for_unit(&mut deps, context, unit, &mut visited).is_ok();
-    let basedir = None; // TODO
+    let basedir_string;
+    let basedir = match context.config.get_path("build.dep-info-basedir")? {
+        Some(value) => {
+            basedir_string = value.val.as_os_str().to_str().
+              ok_or_else(|| internal("build.dep-info-basedir path not utf-8"))?.to_string();
+            Some(basedir_string.as_str())
+        }
+        None => None,
+    };
     for &(_, ref link_dst, _) in context.target_filenames(unit)?.iter() {
         if let Some(ref link_dst) = *link_dst {
             let output_path = link_dst.with_extension("d");

src/doc/src/reference/config.md

@@ -104,6 +104,7 @@ target = "triple"         # build for the target triple
 target-dir = "target"     # path of where to place all generated artifacts
 rustflags = ["..", ".."]  # custom flags to pass to all compiler invocations
 incremental = true        # whether or not to enable incremental compilation
+dep-info-basedir = ".."   # full path for the base directory for targets in depfiles
 
 [term]
 verbose = false        # whether cargo provides verbose output