feat(tree): Auto-detect '--charset' mode

Cargo.toml

@@ -203,6 +203,7 @@ unicase.workspace = true
 unicode-width.workspace = true
 url.workspace = true
 walkdir.workspace = true
+supports-unicode = "2.1.0"
 
 [target.'cfg(target_os = "linux")'.dependencies]
 cargo-credential-libsecret.workspace = true

src/bin/cargo/commands/tree.rs

@@ -7,6 +7,7 @@ use cargo::ops::Packages;
 use cargo::util::print_available_packages;
 use cargo::util::CargoResult;
 use std::collections::HashSet;
+use std::io::IsTerminal as _;
 use std::str::FromStr;
 
 pub fn cli() -> Command {
@@ -69,8 +70,7 @@ pub fn cli() -> Command {
         .arg(
             opt("charset", "Character set to use in output")
                 .value_name("CHARSET")
-                .value_parser(["utf8", "ascii"])
-                .default_value("utf8"),
+                .value_parser(["utf8", "ascii"]),
         )
         .arg(
             opt("format", "Format string used for printing dependencies")
@@ -184,8 +184,18 @@ subtree of the package given to -p.\n\
         print_available_packages(&ws)?;
     }
 
-    let charset = tree::Charset::from_str(args.get_one::<String>("charset").unwrap())
+    let charset = args.get_one::<String>("charset");
+    let charset = charset
+        .map(|c| tree::Charset::from_str(c))
+        .transpose()
         .map_err(|e| anyhow::anyhow!("{}", e))?;
+    let charset = charset.unwrap_or_else(|| {
+        if supports_unicode::supports_unicode() || !std::io::stdout().is_terminal() {
+            tree::Charset::Utf8
+        } else {
+            tree::Charset::Ascii
+        }
+    });
     let opts = tree::TreeOptions {
         cli_features: args.cli_features()?,
         packages,

src/doc/man/cargo-tree.md

@@ -150,7 +150,7 @@ The default is the host platform. Use the value `all` to include *all* targets.
 
 {{#option "`--charset` _charset_" }}
 Chooses the character set to use for the tree. Valid values are "utf8" or
-"ascii". Default is "utf8".
+"ascii". When unspecified, cargo will auto-select a value.
 {{/option}}
 
 {{#option "`-f` _format_" "`--format` _format_" }}

src/doc/man/generated_txt/cargo-tree.txt

@@ -141,7 +141,8 @@ OPTIONS
    Tree Formatting Options
        --charset charset
            Chooses the character set to use for the tree. Valid values are
-           “utf8” or “ascii”. Default is “utf8”.
+           “utf8” or “ascii”. When unspecified, cargo will auto-select
+           a value.
 
        -f format, --format format
            Set the format string for each package. The default is “{p}”.

src/doc/src/commands/cargo-tree.md

@@ -146,7 +146,7 @@ The default is the host platform. Use the value <code>all</code> to include <em>
 
 <dt class="option-term" id="option-cargo-tree---charset"><a class="option-anchor" href="#option-cargo-tree---charset"></a><code>--charset</code> <em>charset</em></dt>
 <dd class="option-desc">Chooses the character set to use for the tree. Valid values are “utf8” or
-“ascii”. Default is “utf8”.</dd>
+“ascii”. When unspecified, cargo will auto-select a value.</dd>
 
 
 <dt class="option-term" id="option-cargo-tree--f"><a class="option-anchor" href="#option-cargo-tree--f"></a><code>-f</code> <em>format</em></dt>

src/etc/man/cargo-tree.1

@@ -175,7 +175,7 @@ The default is the host platform. Use the value \fBall\fR to include \fIall\fR t
 \fB\-\-charset\fR \fIcharset\fR
 .RS 4
 Chooses the character set to use for the tree. Valid values are \[lq]utf8\[rq] or
-\[lq]ascii\[rq]\&. Default is \[lq]utf8\[rq]\&.
+\[lq]ascii\[rq]\&. When unspecified, cargo will auto\-select a value.
 .RE
 .sp
 \fB\-f\fR \fIformat\fR, 

tests/testsuite/cargo_tree/help/stdout.log

@@ -12,8 +12,7 @@ Options:
                             indent] [possible values: depth, indent, none]
       --no-dedupe           Do not de-duplicate (repeats all shared dependencies)
   -d, --duplicates          Show only dependencies which come in multiple versions (implies -i)
-      --charset <CHARSET>   Character set to use in output [default: utf8] [possible values: utf8,
-                            ascii]
+      --charset <CHARSET>   Character set to use in output [possible values: utf8, ascii]
   -f, --format <FORMAT>     Format string used for printing dependencies [default: {p}]
   -v, --verbose...          Use verbose output (-vv very verbose/build.rs output)
   -q, --quiet               Do not print cargo log messages