Fix remap-path-prefix from failing.

src/cargo/core/compiler/fingerprint.rs

@@ -1581,8 +1581,11 @@ pub fn translate_dep_info(
     for file in deps {
         // The path may be absolute or relative, canonical or not. Make sure
         // it is canonicalized so we are comparing the same kinds of paths.
-        let canon_file = rustc_cwd.join(file).canonicalize()?;
         let abs_file = rustc_cwd.join(file);
+        // If canonicalization fails, just use the abs path. There is currently
+        // a bug where --remap-path-prefix is affecting .d files, causing them
+        // to point to non-existent paths.
+        let canon_file = abs_file.canonicalize().unwrap_or_else(|_| abs_file.clone());
 
         let (ty, path) = if let Ok(stripped) = canon_file.strip_prefix(&target_root) {
             (DepInfoPathType::TargetRootRelative, stripped)

tests/testsuite/rustflags.rs

@@ -1,8 +1,10 @@
 use std::fs::{self, File};
 use std::io::Write;
 
-use crate::support::rustc_host;
-use crate::support::{basic_lib_manifest, basic_manifest, paths, project, project_in_home};
+use crate::support::registry::Package;
+use crate::support::{
+    basic_lib_manifest, basic_manifest, paths, project, project_in_home, rustc_host,
+};
 
 #[cargo_test]
 fn env_rustflags_normal_source() {
@@ -1393,3 +1395,41 @@ fn remap_path_prefix_ignored() {
         .run();
     check_metadata_same();
 }
+
+#[cargo_test]
+fn remap_path_prefix_works() {
+    // Check that remap-path-prefix works.
+    Package::new("bar", "0.1.0")
+        .file("src/lib.rs", "pub fn f() -> &'static str { file!() }")
+        .publish();
+
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+            [package]
+            name = "foo"
+            version = "0.1.0"
+
+            [dependencies]
+            bar = "0.1"
+            "#,
+        )
+        .file(
+            "src/main.rs",
+            r#"
+            fn main() {
+                println!("{}", bar::f());
+            }
+            "#,
+        )
+        .build();
+
+    p.cargo("run")
+        .env(
+            "RUSTFLAGS",
+            format!("--remap-path-prefix={}=/foo", paths::root().display()),
+        )
+        .with_stdout("/foo/home/.cargo/registry/src/[..]/bar-0.1.0/src/lib.rs")
+        .run();
+}