Implement -Zfix-edition

This adds the implementation for the behavior of `cargo fix
-Zfix-edition`.

src/bin/cargo/commands/fix.rs

@@ -91,10 +91,7 @@ pub fn exec(gctx: &mut GlobalContext, args: &ArgMatches) -> CliResult {
 
     let allow_dirty = args.flag("allow-dirty");
 
-    ops::fix(
-        gctx,
-        &ws,
-        &mut ops::FixOptions {
+    let mut opts = ops::FixOptions {
         edition: args
             .flag("edition")
             .then_some(ops::EditionFixMode::NextRelative),
@@ -105,7 +102,13 @@ pub fn exec(gctx: &mut GlobalContext, args: &ArgMatches) -> CliResult {
         allow_no_vcs: args.flag("allow-no-vcs"),
         broken_code: args.flag("broken-code"),
         requested_lockfile_path: lockfile_path,
-        },
-    )?;
+    };
+
+    if let Some(fe) = &gctx.cli_unstable().fix_edition {
+        ops::fix_edition(gctx, &ws, &mut opts, fe)?;
+    } else {
+        ops::fix(gctx, &ws, &mut opts)?;
+    }
+
     Ok(())
 }

src/cargo/ops/fix/fix_edition.rs

@@ -0,0 +1,108 @@
+//! Support for the permanently unstable `-Zfix-edition` flag.
+
+use super::{EditionFixMode, FixOptions};
+use crate::core::features::{Edition, FixEdition};
+use crate::core::{Package, Workspace};
+use crate::ops;
+use crate::util::toml_mut::manifest::LocalManifest;
+use crate::{CargoResult, GlobalContext};
+use toml_edit::{Formatted, Item, Value};
+
+/// Performs the actions for the `-Zfix-edition` flag.
+pub fn fix_edition(
+    gctx: &GlobalContext,
+    original_ws: &Workspace<'_>,
+    opts: &mut FixOptions,
+    fix_edition: &FixEdition,
+) -> CargoResult<()> {
+    let packages = opts.compile_opts.spec.get_packages(original_ws)?;
+    let skip_if_not_edition = |edition| -> CargoResult<bool> {
+        if !packages.iter().all(|p| p.manifest().edition() == edition) {
+            gctx.shell().status(
+                "Skipping",
+                &format!("not all packages are at edition {edition}"),
+            )?;
+            Ok(true)
+        } else {
+            Ok(false)
+        }
+    };
+
+    match fix_edition {
+        FixEdition::Start(edition) => {
+            // The start point just runs `cargo check` if the edition is the
+            // starting edition. This is so that crater can set a baseline of
+            // whether or not the package builds at all. For other editions,
+            // we skip entirely since they are not of interest since we can't
+            // migrate them.
+            if skip_if_not_edition(*edition)? {
+                return Ok(());
+            }
+            ops::compile(&original_ws, &opts.compile_opts)?;
+        }
+        FixEdition::End { initial, next } => {
+            // Skip packages that are not the starting edition, since we can
+            // only migrate from one edition to the next.
+            if skip_if_not_edition(*initial)? {
+                return Ok(());
+            }
+            // Do the edition fix.
+            opts.edition = Some(EditionFixMode::OverrideSpecific(*next));
+            opts.allow_dirty = true;
+            opts.allow_no_vcs = true;
+            opts.allow_staged = true;
+            ops::fix(gctx, original_ws, opts)?;
+            // Do `cargo check` with the new edition so that we can verify
+            // that it also works on the next edition.
+            replace_edition(&packages, *next)?;
+            gctx.shell()
+                .status("Updated", &format!("edition to {next}"))?;
+            let ws = original_ws.reload(gctx)?;
+            // Unset these since we just want to do a normal `cargo check`.
+            *opts
+                .compile_opts
+                .build_config
+                .rustfix_diagnostic_server
+                .borrow_mut() = None;
+            opts.compile_opts.build_config.primary_unit_rustc = None;
+
+            ops::compile(&ws, &opts.compile_opts)?;
+        }
+    }
+    Ok(())
+}
+
+/// Modifies the `edition` value of the given packages to the new edition.
+fn replace_edition(packages: &[&Package], to_edition: Edition) -> CargoResult<()> {
+    for package in packages {
+        let mut manifest_mut = LocalManifest::try_new(package.manifest_path())?;
+        let document = &mut manifest_mut.data;
+        let root = document.as_table_mut();
+        // Update edition to the new value.
+        if let Some(package) = root.get_mut("package").and_then(|t| t.as_table_like_mut()) {
+            package.insert(
+                "edition",
+                Item::Value(Value::String(Formatted::new(to_edition.to_string()))),
+            );
+        }
+        // If the edition is unstable, add it to cargo-features.
+        if !to_edition.is_stable() {
+            let feature = "unstable-editions";
+
+            if let Some(features) = root
+                .entry("cargo-features")
+                .or_insert_with(|| Item::Value(Value::Array(toml_edit::Array::new())))
+                .as_array_mut()
+            {
+                if !features
+                    .iter()
+                    .any(|f| f.as_str().map_or(false, |f| f == feature))
+                {
+                    features.push(feature);
+                }
+            }
+        }
+        manifest_mut.write()?;
+    }
+    Ok(())
+}

src/cargo/ops/fix/mod.rs

@@ -51,6 +51,7 @@ use rustfix::CodeFix;
 use semver::Version;
 use tracing::{debug, trace, warn};
 
+pub use self::fix_edition::fix_edition;
 use crate::core::compiler::CompileKind;
 use crate::core::compiler::RustcTargetData;
 use crate::core::resolver::features::{DiffMap, FeatureOpts, FeatureResolver, FeaturesFor};
@@ -66,6 +67,8 @@ use crate::util::GlobalContext;
 use crate::util::{existing_vcs_repo, LockServer, LockServerClient};
 use crate::{drop_eprint, drop_eprintln};
 
+mod fix_edition;
+
 /// **Internal only.**
 /// Indicates Cargo is in fix-proxy-mode if presents.
 /// The value of it is the socket address of the [`LockServer`] being used.

src/cargo/ops/mod.rs

@@ -26,7 +26,9 @@ pub use self::cargo_update::upgrade_manifests;
 pub use self::cargo_update::write_manifest_upgrades;
 pub use self::cargo_update::UpdateOptions;
 pub use self::common_for_install_and_uninstall::{resolve_root, InstallTracker};
-pub use self::fix::{fix, fix_exec_rustc, fix_get_proxy_lock_addr, EditionFixMode, FixOptions};
+pub use self::fix::{
+    fix, fix_edition, fix_exec_rustc, fix_get_proxy_lock_addr, EditionFixMode, FixOptions,
+};
 pub use self::lockfile::{load_pkg_lockfile, resolve_to_string, write_pkg_lockfile};
 pub use self::registry::info;
 pub use self::registry::modify_owners;

tests/testsuite/fix.rs

@@ -2963,3 +2963,103 @@ dep_df_false = { workspace = true, default-features = false }
 "#]],
     );
 }
+
+#[cargo_test]
+fn fix_edition_skips_old_editions() {
+    // Checks that -Zfix-edition will skip things that are not 2024.
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"[workspace]
+            members = ["e2021", "e2024"]
+            resolver = "3"
+            "#,
+        )
+        .file(
+            "e2021/Cargo.toml",
+            r#"
+            [package]
+            name = "e2021"
+            edition = "2021"
+            "#,
+        )
+        .file("e2021/src/lib.rs", "")
+        .file(
+            "e2024/Cargo.toml",
+            r#"
+                [package]
+                name = "e2024"
+                edition = "2024"
+            "#,
+        )
+        .file("e2024/src/lib.rs", "")
+        .build();
+
+    // Doing the whole workspace should skip since there is a 2021 in the mix.
+    p.cargo("fix -Zfix-edition=start=2024 -v")
+        .masquerade_as_nightly_cargo(&["fix-edition"])
+        .with_stderr_data(str![[r#"
+[SKIPPING] not all packages are at edition 2024
+
+"#]])
+        .run();
+
+    // Same with `end`.
+    p.cargo("fix -Zfix-edition=end=2024,future -v")
+        .masquerade_as_nightly_cargo(&["fix-edition"])
+        .with_stderr_data(str![[r#"
+[SKIPPING] not all packages are at edition 2024
+
+"#]])
+        .run();
+
+    // Doing an individual package at the correct edition should check it.
+    p.cargo("fix -Zfix-edition=start=2024 -p e2024")
+        .masquerade_as_nightly_cargo(&["fix-edition"])
+        .with_stderr_data(str![[r#"
+[CHECKING] e2024 v0.0.0 ([ROOT]/foo/e2024)
+[FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
+
+"#]])
+        .run();
+}
+
+#[cargo_test(nightly, reason = "future edition is always unstable")]
+fn fix_edition_future() {
+    // Checks that the -Zfix-edition can work for the future.
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+            [package]
+            name = "foo"
+            edition = "2024""#,
+        )
+        .file("src/lib.rs", "")
+        .build();
+
+    p.cargo("fix -Zfix-edition=end=2024,future")
+        .masquerade_as_nightly_cargo(&["fix-edition"])
+        .with_stderr_data(str![[r#"
+[MIGRATING] Cargo.toml from 2024 edition to future
+[CHECKING] foo v0.0.0 ([ROOT]/foo)
+[MIGRATING] src/lib.rs from 2024 edition to future
+[FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
+     Updated edition to future
+[CHECKING] foo v0.0.0 ([ROOT]/foo)
+[FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
+
+"#]])
+        .run();
+    assert_e2e().eq(
+        p.read_file("Cargo.toml"),
+        str![[r#"
+cargo-features = ["unstable-editions"]
+
+            [package]
+            name = "foo"
+edition = "future"
+
+"#]],
+    );
+}

triagebot.toml

@@ -279,7 +279,7 @@ trigger_files = ["src/bin/cargo/commands/fetch.rs", "src/cargo/ops/cargo_fetch.r
 trigger_files = [
     "crates/rustfix/",
     "src/bin/cargo/commands/fix.rs",
-    "src/cargo/ops/fix.rs",
+    "src/cargo/ops/fix/",
     "src/cargo/util/diagnostic_server.rs",
     "src/cargo/util/lockserver.rs",
 ]