Don't use debug display for error object.

src/cargo/lib.rs

@@ -117,7 +117,7 @@ pub fn exit_with_error(err: CliError, shell: &mut Shell) -> ! {
 /// Displays an error, and all its causes, to stderr.
 pub fn display_error(err: &Error, shell: &mut Shell) {
     debug!("display_error; err={:?}", err);
-    let has_verbose = _display_error(err, shell);
+    let has_verbose = _display_error(err, shell, true);
     if has_verbose {
         drop(writeln!(
             shell.err(),
@@ -140,7 +140,15 @@ pub fn display_error(err: &Error, shell: &mut Shell) {
     }
 }
 
-fn _display_error(err: &Error, shell: &mut Shell) -> bool {
+/// Displays a warning, with an error object providing detailed information
+/// and context.
+pub fn display_warning_with_error(warning: &str, err: &Error, shell: &mut Shell) {
+    drop(shell.warn(warning));
+    drop(writeln!(shell.err(), ""));
+    _display_error(err, shell, false);
+}
+
+fn _display_error(err: &Error, shell: &mut Shell, as_err: bool) -> bool {
     let verbosity = shell.verbosity();
     let is_verbose = |e: &(dyn std::error::Error + 'static)| -> bool {
         verbosity != Verbose && e.downcast_ref::<VerboseError>().is_some()
@@ -149,7 +157,11 @@ fn _display_error(err: &Error, shell: &mut Shell) -> bool {
     if is_verbose(err.as_ref()) {
         return true;
     }
-    drop(shell.error(&err));
+    if as_err {
+        drop(shell.error(&err));
+    } else {
+        drop(writeln!(shell.err(), "{}", err));
+    }
     for cause in err.chain().skip(1) {
         // If we're not in verbose mode then print remaining errors until one
         // marked as `VerboseError` appears.

src/cargo/ops/cargo_doc.rs

@@ -104,10 +104,8 @@ fn open_docs(path: &Path, shell: &mut Shell) -> CargoResult<()> {
         }
         None => {
             if let Err(e) = opener::open(&path) {
-                shell.warn(format!("Couldn't open docs: {}", e))?;
-                for cause in anyhow::Error::new(e).chain().skip(1) {
-                    shell.warn(format!("Caused by:\n {}", cause))?;
-                }
+                let e = e.into();
+                crate::display_warning_with_error("couldn't open docs", &e, shell);
             }
         }
     };

src/cargo/ops/cargo_new.rs

@@ -762,12 +762,12 @@ mod tests {
     }
 
     if let Err(e) = Workspace::new(&path.join("Cargo.toml"), config) {
-        let msg = format!(
+        crate::display_warning_with_error(
             "compiling this new crate may not work due to invalid \
-             workspace configuration\n\n{:?}",
-            e,
+             workspace configuration",
+            &e,
+            &mut config.shell(),
         );
-        config.shell().warn(msg)?;
     }
 
     Ok(())

tests/testsuite/workspaces.rs

@@ -1037,8 +1037,7 @@ fn new_warns_you_this_will_not_work() {
         .env("USER", "foo")
         .with_stderr(
             "\
-warning: compiling this new crate may not work due to invalid workspace \
-configuration
+warning: compiling this new crate may not work due to invalid workspace configuration
 
 current package believes it's in a workspace when it's not:
 current: [..]
@@ -1065,8 +1064,10 @@ fn new_warning_with_corrupt_ws() {
 failed to parse manifest at `[..]foo/Cargo.toml`
 
 Caused by:
-    0: could not parse input as TOML
-    1: expected an equals, found eof at line 1 column 5
+  could not parse input as TOML
+
+Caused by:
+  expected an equals, found eof at line 1 column 5
      Created binary (application) `bar` package
 ",
         )