Have it env use quoted/debug form when newlines are present

In addition to any invalid Unicode and double quotes, as before.

+ Revise its documentation.

Author: EliahKagan

tests/it/src/args.rs

@@ -78,16 +78,15 @@ pub enum Subcommands {
     /// It is useful to be able to observe environment variables that are set when running code
     /// with tools such as `cargo` or `cross`. Commands like `cargo run -p internal-tools -- env`
     /// include environment changes from `cargo` itself. With `cross`, changes are more extensive,
-    /// due to the effect of `build.env.passthrough`, container customization, and existing special
+    /// due to effects of `build.env.passthrough`, container customization, and preexisting special
     /// cases in wrapper scripts shipped in default `cross` containers (such as to `LD_PRELOAD`).
     ///
     /// Since one use for checking environment variables is to investigate the effects of
     /// environments that contain variable names or values that are not valid Unicode, this avoids
     /// requiring that environment variables all be Unicode. Any name or value that is not Unicode
-    /// is shown in its Rust debug representation. This is always quoted, and to decrease ambiguity
-    /// any name or (more likely) value that contains literal double quotes is likewise shown in
-    /// its debug representation so that it is always clear if a quotation mark is just for
-    /// display. Each name and value is otherwise shown literally.
+    /// is shown in its Rust debug representation. This is always quoted. To decrease ambiguity,
+    /// any name or value containing a literal double quote or newline is also shown in its debug
+    /// representation. Names and values without such content are shown literally and not quoted.
     #[clap(visible_alias = "e")]
     Env {},
 }

tests/it/src/commands/env.rs

@@ -8,7 +8,7 @@ pub(super) mod function {
 
     fn repr(text: &std::ffi::OsStr) -> String {
         text.to_str()
-            .filter(|s| !s.contains('"'))
+            .filter(|s| !s.chars().any(|c| c == '"' || c == '\n'))
             .map(ToOwned::to_owned)
             .unwrap_or_else(|| format!("{text:?}"))
     }