Move ELF note parsing into cargo-subcommand-metadata optional feature

Author: dtolnay

Cargo.toml

@@ -19,6 +19,7 @@ path = "src/cargo/lib.rs"
 atty = "0.2"
 bytesize = "1.0"
 cargo-platform = { path = "crates/cargo-platform", version = "0.1.2" }
+cargo-subcommand-metadata = { path = "crates/cargo-subcommand-metadata", version = "0.1.0", features = ["parse"] }
 cargo-util = { path = "crates/cargo-util", version = "0.2.1" }
 crates-io = { path = "crates/crates-io", version = "0.34.0" }
 crossbeam-utils = "0.8"
@@ -74,11 +75,6 @@ itertools = "0.10.0"
 # for more information.
 rustc-workspace-hack = "1.0.0"
 
-[target.'cfg(target_os = "linux")'.dependencies]
-cargo-subcommand-metadata = { path = "crates/cargo-subcommand-metadata", version = "0.1.0" }
-memmap = "0.7"
-object = "0.28"
-
 [target.'cfg(windows)'.dependencies]
 fwdansi = "1.1.0"
 

crates/cargo-subcommand-metadata/Cargo.toml

@@ -5,3 +5,10 @@ edition = "2021"
 license = "MIT OR Apache-2.0"
 repository = "https://github.com/rust-lang/cargo"
 description = "Embed metadata into a Cargo subcommand, so that `cargo --list` can show a description of the subcommand"
+
+[target.'cfg(target_os = "linux")'.dependencies]
+memmap = { version = "0.7", optional = true }
+object = { version = "0.28", optional = true }
+
+[features]
+parse = ["memmap", "object"]

crates/cargo-subcommand-metadata/src/lib.rs

@@ -1,3 +1,6 @@
+#[cfg(feature = "parse")]
+pub mod parse;
+
 /// Cargo's name for the purpose of ELF notes.
 ///
 /// The `name` field of an ELF note is designated to hold the entry's "owner" or
@@ -82,16 +85,14 @@ macro_rules! description {
 
                 #[used]
                 #[link_section = ".note.cargo.subcommand"]
-                static ELF_NOTE: ElfNote = {
-                    ElfNote {
-                        namesz: $crate::ELF_NOTE_NAME.len() as u32 + 1,
-                        descsz: CARGO_SUBCOMMAND_DESCRIPTION.len() as u32,
-                        ty: $crate::ElfNoteType::Description,
-                        name: unsafe { *$crate::ELF_NOTE_NAME.as_ptr().cast() },
-                        name_padding: $crate::private::padding(),
-                        desc: unsafe { *CARGO_SUBCOMMAND_DESCRIPTION.as_ptr().cast() },
-                        desc_padding: $crate::private::padding(),
-                    }
+                static ELF_NOTE: ElfNote = ElfNote {
+                    namesz: $crate::ELF_NOTE_NAME.len() as u32 + 1,
+                    descsz: CARGO_SUBCOMMAND_DESCRIPTION.len() as u32,
+                    ty: $crate::ElfNoteType::Description,
+                    name: unsafe { *$crate::ELF_NOTE_NAME.as_ptr().cast() },
+                    name_padding: $crate::private::padding(),
+                    desc: unsafe { *CARGO_SUBCOMMAND_DESCRIPTION.as_ptr().cast() },
+                    desc_padding: $crate::private::padding(),
                 };
             };
         };

src/bin/cargo/subcommand_metadata.rs renamed to crates/cargo-subcommand-metadata/src/parse.rs

@@ -1,6 +1,6 @@
 use std::path::Path;
 
-pub(crate) fn description(path: &Path) -> Option<String> {
+pub fn description(path: &Path) -> Option<String> {
     implementation::description(path)
 }
 
@@ -29,9 +29,8 @@ mod implementation {
             if section_header.name(endian, string_table).ok() == Some(b".note.cargo.subcommand") {
                 if let Ok(Some(mut notes)) = section_header.notes(endian, data) {
                     while let Ok(Some(note)) = notes.next() {
-                        if note.name() == cargo_subcommand_metadata::ELF_NOTE_NAME.as_bytes()
-                            && note.n_type(endian)
-                                == cargo_subcommand_metadata::ElfNoteType::Description as u32
+                        if note.name() == crate::ELF_NOTE_NAME.as_bytes()
+                            && note.n_type(endian) == crate::ElfNoteType::Description as u32
                         {
                             if description.is_some() {
                                 return None;

src/bin/cargo/cli.rs

@@ -1,6 +1,7 @@
 use anyhow::anyhow;
 use cargo::core::{features, CliUnstable};
 use cargo::{self, drop_print, drop_println, CliResult, Config};
+use cargo_subcommand_metadata as subcommand_metadata;
 use clap::{
     error::{ContextKind, ContextValue},
     AppSettings, Arg, ArgMatches,
@@ -12,7 +13,6 @@ use std::fmt::Write;
 use super::commands;
 use super::list_commands;
 use crate::command_prelude::*;
-use crate::subcommand_metadata;
 use cargo::core::features::HIDDEN;
 
 lazy_static::lazy_static! {
@@ -148,7 +148,7 @@ Run with 'cargo -Z [FLAG] [SUBCOMMAND]'",
                 CommandInfo::External { path } => {
                     if let Some(desc) = known_external_desc {
                         drop_println!(config, "    {:<20} {}", name, desc);
-                    } else if let Some(desc) = subcommand_metadata::description(&path) {
+                    } else if let Some(desc) = subcommand_metadata::parse::description(&path) {
                         drop_println!(config, "    {:<20} {}", name, desc);
                     } else if is_verbose {
                         drop_println!(config, "    {:<20} {}", name, path.display());

src/bin/cargo/main.rs

@@ -13,7 +13,6 @@ use std::path::{Path, PathBuf};
 
 mod cli;
 mod commands;
-mod subcommand_metadata;
 
 use crate::command_prelude::*;