Don't panic when printing JSON with non-utf8 paths

Before:

    λ cd \Xff/foo/ && cargo verify-project && cargo metadata
    {"success":"true"}
    warning: please specify `--format-version` flag explicitly to avoid compatibility problems
    thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: Error("path contains invalid UTF-8 characters", line: 0, column: 0)', /rustc/a5a775e3f9e8043dad405e00aee0ae60882a7b71/src/tools/cargo/src/cargo/core/shell.rs:346:51
    note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

After:

    λ cd \Xff/foo/ && $cargo verify-project && $cargo metadata
    {"success":"true"}
    warning: please specify `--format-version` flag explicitly to avoid compatibility problems
    error: path contains invalid UTF-8 characters

I am pretty  sure that this has zero real-world impact, but the diff is
small, so why not handle it?

src/bin/cargo/commands/locate_project.rs

@@ -51,7 +51,7 @@ pub fn exec(config: &mut Config, args: &ArgMatches<'_>) -> CliResult {
     let location = ProjectLocation { root };
 
     match MessageFormat::parse(args)? {
-        MessageFormat::Json => config.shell().print_json(&location),
+        MessageFormat::Json => config.shell().print_json(&location)?,
         MessageFormat::Plain => drop_println!(config, "{}", location.root),
     }
 

src/bin/cargo/commands/metadata.rs

@@ -53,6 +53,6 @@ pub fn exec(config: &mut Config, args: &ArgMatches<'_>) -> CliResult {
     };
 
     let result = ops::output_metadata(&ws, &options)?;
-    config.shell().print_json(&result);
+    config.shell().print_json(&result)?;
     Ok(())
 }

src/bin/cargo/commands/read_manifest.rs

@@ -15,6 +15,8 @@ Deprecated, use `cargo metadata --no-deps` instead.\
 
 pub fn exec(config: &mut Config, args: &ArgMatches<'_>) -> CliResult {
     let ws = args.workspace(config)?;
-    config.shell().print_json(&ws.current()?.serialized(config));
+    config
+        .shell()
+        .print_json(&ws.current()?.serialized(config))?;
     Ok(())
 }

src/bin/cargo/commands/verify_project.rs

@@ -15,12 +15,12 @@ pub fn exec(config: &mut Config, args: &ArgMatches<'_>) -> CliResult {
     if let Err(e) = args.workspace(config) {
         let mut h = HashMap::new();
         h.insert("invalid".to_string(), e.to_string());
-        config.shell().print_json(&h);
+        config.shell().print_json(&h)?;
         process::exit(1)
     }
 
     let mut h = HashMap::new();
     h.insert("success".to_string(), "true".to_string());
-    config.shell().print_json(&h);
+    config.shell().print_json(&h)?;
     Ok(())
 }

src/cargo/core/shell.rs

@@ -342,9 +342,12 @@ impl Shell {
         Ok(())
     }
 
-    pub fn print_json<T: serde::ser::Serialize>(&mut self, obj: &T) {
-        let encoded = serde_json::to_string(&obj).unwrap();
+    pub fn print_json<T: serde::ser::Serialize>(&mut self, obj: &T) -> CargoResult<()> {
+        // Path may fail to serialize to JSON ...
+        let encoded = serde_json::to_string(&obj)?;
+        // ... but don't fail due to a closed pipe.
         drop(writeln!(self.out(), "{}", encoded));
+        Ok(())
     }
 }
 

tests/testsuite/metadata.rs

@@ -2953,3 +2953,29 @@ fn dep_kinds_workspace() {
         )
         .run();
 }
+
+// Creating non-utf8 path is an OS-specific pain, so let's run this only on
+// linux, where arbitrary bytes work.
+#[cfg(target_os = "linux")]
+#[cargo_test]
+fn cargo_metadata_non_utf8() {
+    use std::ffi::OsString;
+    use std::os::unix::ffi::OsStringExt;
+    use std::path::PathBuf;
+
+    let base = PathBuf::from(OsString::from_vec(vec![255]));
+
+    let p = project()
+        .no_manifest()
+        .file(base.join("./src/lib.rs"), "")
+        .file(base.join("./Cargo.toml"), &basic_lib_manifest("foo"))
+        .build();
+
+    p.cargo("metadata")
+        .cwd(p.root().join(base))
+        .arg("--format-version")
+        .arg("1")
+        .with_stderr("error: path contains invalid UTF-8 characters")
+        .with_status(101)
+        .run();
+}