feat(resolver): Stabilize resolver v3 (#14754)

### What does this PR try to resolve?

This is a follow up to #14639 in prep for Edition 2024

### How should we test and review this PR?

This is stacked on #14753

### Additional information

src/cargo/util/toml/mod.rs

@@ -273,12 +273,6 @@ fn normalize_toml(
     warnings: &mut Vec<String>,
     errors: &mut Vec<String>,
 ) -> CargoResult<manifest::TomlManifest> {
-    if let Some(workspace) = &original_toml.workspace {
-        if workspace.resolver.as_deref() == Some("3") {
-            features.require(Feature::edition2024())?;
-        }
-    }
-
     let mut normalized_toml = manifest::TomlManifest {
         cargo_features: original_toml.cargo_features.clone(),
         package: None,
@@ -316,8 +310,7 @@ fn normalize_toml(
     if let Some(original_package) = original_toml.package() {
         let package_name = &original_package.name;
 
-        let normalized_package =
-            normalize_package_toml(original_package, features, package_root, &inherit)?;
+        let normalized_package = normalize_package_toml(original_package, package_root, &inherit)?;
         let edition = normalized_package
             .normalized_edition()
             .expect("previously normalized")
@@ -549,7 +542,6 @@ fn normalize_patch<'a>(
 #[tracing::instrument(skip_all)]
 fn normalize_package_toml<'a>(
     original_package: &manifest::TomlPackage,
-    features: &Features,
     package_root: &Path,
     inherit: &dyn Fn() -> CargoResult<&'a InheritableFields>,
 ) -> CargoResult<Box<manifest::TomlPackage>> {
@@ -682,10 +674,6 @@ fn normalize_package_toml<'a>(
         _invalid_cargo_features: Default::default(),
     };
 
-    if normalized_package.resolver.as_deref() == Some("3") {
-        features.require(Feature::edition2024())?;
-    }
-
     Ok(Box::new(normalized_package))
 }
 

src/doc/src/reference/config.md

@@ -981,7 +981,7 @@ The `[resolver]` table overrides [dependency resolution behavior](resolver.md) f
 
 #### `resolver.incompatible-rust-versions`
 * Type: string
-* Default: `"allow"`
+* Default: See [`resolver`](resolver.md#resolver-versions) docs
 * Environment: `CARGO_RESOLVER_INCOMPATIBLE_RUST_VERSIONS`
 
 When resolving which version of a dependency to use, select how versions with incompatible `package.rust-version`s are treated.

src/doc/src/reference/resolver.md

@@ -507,6 +507,7 @@ resolver = "2"
 - `"2"` ([`edition = "2021"`](manifest.md#the-edition-field) default): Introduces changes in [feature
 unification](#features). See the [features chapter][features-2] for more
 details.
+- `"3"` (requires Rust 1.84+): Change the default for [`resolver.incompatible-rust-versions`] from `allow` to `fallback`
 
 The resolver is a global option that affects the entire workspace. The
 `resolver` version in dependencies is ignored, only the value in the top-level

tests/testsuite/rust_version.rs

@@ -612,7 +612,7 @@ foo v0.0.1 ([ROOT]/foo)
         .run();
 }
 
-#[cargo_test(nightly, reason = "edition2024 in rustc is unstable")]
+#[cargo_test]
 fn resolve_v3() {
     Package::new("only-newer", "1.6.0")
         .rust_version("1.65.0")
@@ -631,8 +631,6 @@ fn resolve_v3() {
         .file(
             "Cargo.toml",
             r#"
-            cargo-features = ["edition2024"]
-
             [package]
             name = "foo"
             version = "0.0.1"
@@ -651,7 +649,6 @@ fn resolve_v3() {
 
     // v3 should resolve for MSRV
     p.cargo("generate-lockfile")
-        .masquerade_as_nightly_cargo(&["edition2024"])
         .with_stderr_data(str![[r#"
 [UPDATING] `dummy-registry` index
 [LOCKING] 2 packages to latest Rust 1.60.0 compatible versions
@@ -661,7 +658,6 @@ fn resolve_v3() {
 "#]])
         .run();
     p.cargo("tree")
-        .masquerade_as_nightly_cargo(&["edition2024"])
         .with_stdout_data(str![[r#"
 foo v0.0.1 ([ROOT]/foo)
 ├── newer-and-older v1.5.0
@@ -677,10 +673,8 @@ foo v0.0.1 ([ROOT]/foo)
 [LOCKING] 2 packages to latest compatible versions
 
 "#]])
-        .masquerade_as_nightly_cargo(&["edition2024"])
         .run();
     p.cargo("tree")
-        .masquerade_as_nightly_cargo(&["edition2024"])
         .with_stdout_data(str![[r#"
 foo v0.0.1 ([ROOT]/foo)
 ├── newer-and-older v1.6.0
@@ -697,29 +691,13 @@ foo v0.0.1 ([ROOT]/foo)
 [LOCKING] 2 packages to latest compatible versions
 
 "#]])
-        .masquerade_as_nightly_cargo(&["edition2024"])
         .run();
     p.cargo("tree")
-        .masquerade_as_nightly_cargo(&["edition2024"])
         .with_stdout_data(str![[r#"
 foo v0.0.1 ([ROOT]/foo)
 ├── newer-and-older v1.6.0
 └── only-newer v1.6.0
 
-"#]])
-        .run();
-
-    // unstable
-    p.cargo("generate-lockfile")
-        .with_status(101)
-        .with_stderr_data(str![[r#"
-[ERROR] failed to parse manifest at `[ROOT]/foo/Cargo.toml`
-
-Caused by:
-  the cargo feature `edition2024` requires a nightly version of Cargo, but this is the `stable` channel
-  See https://doc.rust-lang.org/book/appendix-07-nightly-rust.html for more information about Rust release channels.
-  See https://doc.rust-lang.org/cargo/reference/unstable.html#edition-2024 for more information about using this feature.
-
 "#]])
         .run();
 }
@@ -946,7 +924,7 @@ fn cargo_install_ignores_msrv_config() {
         .run();
 }
 
-#[cargo_test(nightly, reason = "edition2024 in rustc is unstable")]
+#[cargo_test]
 fn cargo_install_ignores_resolver_v3_msrv_change() {
     Package::new("dep", "1.0.0")
         .rust_version("1.50")
@@ -958,14 +936,12 @@ fn cargo_install_ignores_resolver_v3_msrv_change() {
         .publish();
     Package::new("foo", "0.0.1")
         .rust_version("1.60")
-        .cargo_feature("edition2024")
         .resolver("3")
         .file("src/main.rs", "fn main() {}")
         .dep("dep", "1")
         .publish();
 
     cargo_process("install foo")
-        .masquerade_as_nightly_cargo(&["edition2024"])
         .with_stderr_data(str![[r#"
 [UPDATING] `dummy-registry` index
 [DOWNLOADING] crates ...