Auto merge of #9184 - ehuss:fix-next-edition, r=alexcrichton

Updates to edition handling.

This introduces some updates for edition handling (split into commits for review).  In short:

* `cargo-features = ["edition2021"]` can be used to opt-in to 2021 support without needing to pass around `-Z unstable-options`. I tried to emphasize in the docs that this is only for testing and experimentation.
* Make `"2"` the default resolver for 2021 edition.
* Make `cargo fix --edition` mean the "next" edition from the present one, and support 2021. Also, if already at the latest edition, generate a warning instead an error.
* I decided to allow `cargo fix --edition` from 2018 to 2021 on the nightly channel without an explicit opt-in. It's tricky to implement with an opt-in (see comment in diff).

Partial for #9048.
Fixes #9047.

crates/cargo-test-support/src/lib.rs

@@ -1524,6 +1524,7 @@ fn substitute_macros(input: &str) -> String {
         ("[REPLACING]", "   Replacing"),
         ("[UNPACKING]", "   Unpacking"),
         ("[SUMMARY]", "     Summary"),
+        ("[FIXED]", "       Fixed"),
         ("[FIXING]", "      Fixing"),
         ("[EXE]", env::consts::EXE_SUFFIX),
         ("[IGNORED]", "     Ignored"),
@@ -1534,6 +1535,7 @@ fn substitute_macros(input: &str) -> String {
         ("[LOGOUT]", "      Logout"),
         ("[YANK]", "        Yank"),
         ("[OWNER]", "       Owner"),
+        ("[MIGRATING]", "   Migrating"),
     ];
     let mut result = input.to_owned();
     for &(pat, subst) in &macros {

src/bin/cargo/commands/fix.rs

@@ -41,17 +41,6 @@ pub fn cli() -> App {
                 .long("edition")
                 .help("Fix in preparation for the next edition"),
         )
-        .arg(
-            // This is a deprecated argument, we'll want to phase it out
-            // eventually.
-            Arg::with_name("prepare-for")
-                .long("prepare-for")
-                .help("Fix warnings in preparation of an edition upgrade")
-                .takes_value(true)
-                .possible_values(&["2018"])
-                .conflicts_with("edition")
-                .hidden(true),
-        )
         .arg(
             Arg::with_name("idioms")
                 .long("edition-idioms")
@@ -111,7 +100,6 @@ pub fn exec(config: &mut Config, args: &ArgMatches<'_>) -> CliResult {
         &ws,
         &mut ops::FixOptions {
             edition: args.is_present("edition"),
-            prepare_for: args.value_of("prepare-for"),
             idioms: args.is_present("idioms"),
             compile_opts: opts,
             allow_dirty: args.is_present("allow-dirty"),

src/cargo/core/compiler/compilation.rs

@@ -8,7 +8,7 @@ use semver::Version;
 
 use super::BuildContext;
 use crate::core::compiler::{CompileKind, Metadata, Unit};
-use crate::core::{Edition, Package};
+use crate::core::Package;
 use crate::util::{self, config, join_paths, process, CargoResult, Config, ProcessBuilder};
 
 /// Structure with enough information to run `rustdoc --test`.
@@ -187,9 +187,7 @@ impl<'cfg> Compilation<'cfg> {
         let rustdoc = process(&*self.config.rustdoc()?);
         let cmd = fill_rustc_tool_env(rustdoc, unit);
         let mut p = self.fill_env(cmd, &unit.pkg, script_meta, unit.kind, true)?;
-        if unit.target.edition() != Edition::Edition2015 {
-            p.arg(format!("--edition={}", unit.target.edition()));
-        }
+        unit.target.edition().cmd_edition_arg(&mut p);
 
         for crate_type in unit.target.rustc_crate_types() {
             p.arg("--crate-type").arg(crate_type.as_str());

src/cargo/core/compiler/mod.rs

@@ -52,7 +52,7 @@ pub use crate::core::compiler::unit::{Unit, UnitInterner};
 use crate::core::features::nightly_features_allowed;
 use crate::core::manifest::TargetSourcePath;
 use crate::core::profiles::{PanicStrategy, Profile, Strip};
-use crate::core::{Edition, Feature, PackageId, Target};
+use crate::core::{Feature, PackageId, Target};
 use crate::util::errors::{self, CargoResult, CargoResultExt, ProcessError, VerboseError};
 use crate::util::interning::InternedString;
 use crate::util::machine_message::Message;
@@ -747,9 +747,7 @@ fn build_base_args(
     cmd.arg("--crate-name").arg(&unit.target.crate_name());
 
     let edition = unit.target.edition();
-    if edition != Edition::Edition2015 {
-        cmd.arg(format!("--edition={}", edition));
-    }
+    edition.cmd_edition_arg(cmd);
 
     add_path_args(bcx.ws, unit, cmd);
     add_error_format_and_color(cx, cmd, cx.rmeta_required(unit));

src/cargo/core/features.rs

@@ -101,7 +101,7 @@ use anyhow::{bail, Error};
 use serde::{Deserialize, Serialize};
 
 use crate::util::errors::CargoResult;
-use crate::util::indented_lines;
+use crate::util::{indented_lines, ProcessBuilder};
 
 pub const SEE_CHANNELS: &str =
     "See https://doc.rust-lang.org/book/appendix-07-nightly-rust.html for more information \
@@ -118,15 +118,117 @@ pub enum Edition {
     Edition2021,
 }
 
+// Adding a new edition:
+// - Add the next edition to the enum.
+// - Update every match expression that now fails to compile.
+// - Update the `FromStr` impl.
+// - Update CLI_VALUES to include the new edition.
+// - Set LATEST_UNSTABLE to Some with the new edition.
+// - Add an unstable feature to the features! macro below for the new edition.
+// - Gate on that new feature in TomlManifest::to_real_manifest.
+// - Update the shell completion files.
+// - Update any failing tests (hopefully there are very few).
+//
+// Stabilization instructions:
+// - Set LATEST_UNSTABLE to None.
+// - Set LATEST_STABLE to the new version.
+// - Update `is_stable` to `true`.
+// - Set the editionNNNN feature to stable in the features macro below.
+// - Update the man page for the --edition flag.
 impl Edition {
+    /// The latest edition that is unstable.
+    ///
+    /// This is `None` if there is no next unstable edition.
+    pub const LATEST_UNSTABLE: Option<Edition> = Some(Edition::Edition2021);
+    /// The latest stable edition.
+    pub const LATEST_STABLE: Edition = Edition::Edition2018;
+    /// Possible values allowed for the `--edition` CLI flag.
+    ///
+    /// This requires a static value due to the way clap works, otherwise I
+    /// would have built this dynamically.
+    pub const CLI_VALUES: &'static [&'static str] = &["2015", "2018", "2021"];
+
+    /// Returns the first version that a particular edition was released on
+    /// stable.
     pub(crate) fn first_version(&self) -> Option<semver::Version> {
         use Edition::*;
         match self {
             Edition2015 => None,
             Edition2018 => Some(semver::Version::new(1, 31, 0)),
+            // FIXME: This will likely be 1.56, update when that seems more likely.
             Edition2021 => Some(semver::Version::new(1, 62, 0)),
         }
     }
+
+    /// Returns `true` if this edition is stable in this release.
+    pub fn is_stable(&self) -> bool {
+        use Edition::*;
+        match self {
+            Edition2015 => true,
+            Edition2018 => true,
+            Edition2021 => false,
+        }
+    }
+
+    /// Returns the previous edition from this edition.
+    ///
+    /// Returns `None` for 2015.
+    pub fn previous(&self) -> Option<Edition> {
+        use Edition::*;
+        match self {
+            Edition2015 => None,
+            Edition2018 => Some(Edition2015),
+            Edition2021 => Some(Edition2018),
+        }
+    }
+
+    /// Returns the next edition from this edition, returning the last edition
+    /// if this is already the last one.
+    pub fn saturating_next(&self) -> Edition {
+        use Edition::*;
+        match self {
+            Edition2015 => Edition2018,
+            Edition2018 => Edition2021,
+            Edition2021 => Edition2021,
+        }
+    }
+
+    /// Updates the given [`ProcessBuilder`] to include the appropriate flags
+    /// for setting the edition.
+    pub(crate) fn cmd_edition_arg(&self, cmd: &mut ProcessBuilder) {
+        if *self != Edition::Edition2015 {
+            cmd.arg(format!("--edition={}", self));
+        }
+        if !self.is_stable() {
+            cmd.arg("-Z").arg("unstable-options");
+        }
+    }
+
+    /// Whether or not this edition supports the `rust_*_compatibility` lint.
+    ///
+    /// Ideally this would not be necessary, but currently 2021 does not have
+    /// any lints, and thus `rustc` doesn't recognize it. Perhaps `rustc`
+    /// could create an empty group instead?
+    pub(crate) fn supports_compat_lint(&self) -> bool {
+        use Edition::*;
+        match self {
+            Edition2015 => false,
+            Edition2018 => true,
+            Edition2021 => false,
+        }
+    }
+
+    /// Whether or not this edition supports the `rust_*_idioms` lint.
+    ///
+    /// Ideally this would not be necessary...
+    pub(crate) fn supports_idiom_lint(&self) -> bool {
+        use Edition::*;
+        match self {
+            Edition2015 => false,
+            Edition2018 => true,
+            Edition2021 => false,
+        }
+    }
 }
 
 impl fmt::Display for Edition {
@@ -282,6 +384,9 @@ features! {
 
     // Specifying a minimal 'rust-version' attribute for crates
     (unstable, rust_version, "", "reference/unstable.html#rust-version"),
+
+    // Support for 2021 edition.
+    (unstable, edition2021, "", "reference/unstable.html#edition-2021"),
 }
 
 const PUBLISH_LOCKFILE_REMOVED: &str = "The publish-lockfile key in Cargo.toml \

src/cargo/core/workspace.rs

@@ -13,7 +13,7 @@ use crate::core::features::Features;
 use crate::core::registry::PackageRegistry;
 use crate::core::resolver::features::RequestedFeatures;
 use crate::core::resolver::ResolveBehavior;
-use crate::core::{Dependency, PackageId, PackageIdSpec};
+use crate::core::{Dependency, Edition, PackageId, PackageIdSpec};
 use crate::core::{EitherManifest, Package, SourceId, VirtualManifest};
 use crate::ops;
 use crate::sources::PathSource;
@@ -88,7 +88,7 @@ pub struct Workspace<'cfg> {
     ignore_lock: bool,
 
     /// The resolver behavior specified with the `resolver` field.
-    resolve_behavior: Option<ResolveBehavior>,
+    resolve_behavior: ResolveBehavior,
 
     /// Workspace-level custom metadata
     custom_metadata: Option<toml::Value>,
@@ -164,10 +164,7 @@ impl<'cfg> Workspace<'cfg> {
             .load_workspace_config()?
             .and_then(|cfg| cfg.custom_metadata);
         ws.find_members()?;
-        ws.resolve_behavior = match ws.root_maybe() {
-            MaybePackage::Package(p) => p.manifest().resolve_behavior(),
-            MaybePackage::Virtual(vm) => vm.resolve_behavior(),
-        };
+        ws.set_resolve_behavior();
         ws.validate()?;
         Ok(ws)
     }
@@ -189,7 +186,7 @@ impl<'cfg> Workspace<'cfg> {
             require_optional_deps: true,
             loaded_packages: RefCell::new(HashMap::new()),
             ignore_lock: false,
-            resolve_behavior: None,
+            resolve_behavior: ResolveBehavior::V1,
             custom_metadata: None,
         }
     }
@@ -203,11 +200,11 @@ impl<'cfg> Workspace<'cfg> {
         let mut ws = Workspace::new_default(current_manifest, config);
         ws.root_manifest = Some(root_path.join("Cargo.toml"));
         ws.target_dir = config.target_dir()?;
-        ws.resolve_behavior = manifest.resolve_behavior();
         ws.packages
             .packages
             .insert(root_path, MaybePackage::Virtual(manifest));
         ws.find_members()?;
+        ws.set_resolve_behavior();
         // TODO: validation does not work because it walks up the directory
         // tree looking for the root which is a fake file that doesn't exist.
         Ok(ws)
@@ -231,7 +228,6 @@ impl<'cfg> Workspace<'cfg> {
         let mut ws = Workspace::new_default(package.manifest_path().to_path_buf(), config);
         ws.is_ephemeral = true;
         ws.require_optional_deps = require_optional_deps;
-        ws.resolve_behavior = package.manifest().resolve_behavior();
         let key = ws.current_manifest.parent().unwrap();
         let id = package.package_id();
         let package = MaybePackage::Package(package);
@@ -244,9 +240,28 @@ impl<'cfg> Workspace<'cfg> {
         ws.members.push(ws.current_manifest.clone());
         ws.member_ids.insert(id);
         ws.default_members.push(ws.current_manifest.clone());
+        ws.set_resolve_behavior();
         Ok(ws)
     }
 
+    fn set_resolve_behavior(&mut self) {
+        // - If resolver is specified in the workspace definition, use that.
+        // - If the root package specifies the resolver, use that.
+        // - If the root package specifies edition 2021, use v2.
+        // - Otherwise, use the default v1.
+        self.resolve_behavior = match self.root_maybe() {
+            MaybePackage::Package(p) => p.manifest().resolve_behavior().or_else(|| {
+                if p.manifest().edition() >= Edition::Edition2021 {
+                    Some(ResolveBehavior::V2)
+                } else {
+                    None
+                }
+            }),
+            MaybePackage::Virtual(vm) => vm.resolve_behavior(),
+        }
+        .unwrap_or(ResolveBehavior::V1);
+    }
+
     /// Returns the current package of this workspace.
     ///
     /// Note that this can return an error if it the current manifest is
@@ -634,7 +649,7 @@ impl<'cfg> Workspace<'cfg> {
     }
 
     pub fn resolve_behavior(&self) -> ResolveBehavior {
-        self.resolve_behavior.unwrap_or(ResolveBehavior::V1)
+        self.resolve_behavior
     }
 
     /// Returns `true` if this workspace uses the new CLI features behavior.
@@ -843,11 +858,11 @@ impl<'cfg> Workspace<'cfg> {
                 if !manifest.patch().is_empty() {
                     emit_warning("patch")?;
                 }
-                if manifest.resolve_behavior().is_some()
-                    && manifest.resolve_behavior() != self.resolve_behavior
-                {
-                    // Only warn if they don't match.
-                    emit_warning("resolver")?;
+                if let Some(behavior) = manifest.resolve_behavior() {
+                    if behavior != self.resolve_behavior {
+                        // Only warn if they don't match.
+                        emit_warning("resolver")?;
+                    }
                 }
             }
         }

src/cargo/ops/cargo_new.rs

@@ -1,4 +1,4 @@
-use crate::core::{Shell, Workspace};
+use crate::core::{Edition, Shell, Workspace};
 use crate::util::errors::{CargoResult, CargoResultExt};
 use crate::util::{existing_vcs_repo, FossilRepo, GitRepo, HgRepo, PijulRepo};
 use crate::util::{paths, restricted_names, Config};
@@ -743,7 +743,7 @@ edition = {}
             },
             match opts.edition {
                 Some(edition) => toml::Value::String(edition.to_string()),
-                None => toml::Value::String("2018".to_string()),
+                None => toml::Value::String(Edition::LATEST_STABLE.to_string()),
             },
             match opts.registry {
                 Some(registry) => format!(