fix(config): Adjust MSRV resolve config field name / values

Fixes rust-lang#13540

src/cargo/core/workspace.rs

@@ -29,7 +29,7 @@ use crate::util::lints::{
 };
 use crate::util::toml::{read_manifest, InheritableFields};
 use crate::util::{
-    context::CargoResolverConfig, context::CargoResolverPrecedence, context::ConfigRelativePath,
+    context::CargoResolverConfig, context::ConfigRelativePath, context::IncompatibleRustVersions,
     Filesystem, GlobalContext, IntoUrl,
 };
 use cargo_util::paths;
@@ -320,19 +320,19 @@ impl<'gctx> Workspace<'gctx> {
         }
         match self.gctx().get::<CargoResolverConfig>("resolver") {
             Ok(CargoResolverConfig {
-                something_like_precedence: Some(precedence),
+                incompatible_rust_versions: Some(incompatible_rust_versions),
             }) => {
                 if self.gctx().cli_unstable().msrv_policy {
                     self.resolve_honors_rust_version =
-                        precedence == CargoResolverPrecedence::SomethingLikeRustVersion;
+                        incompatible_rust_versions == IncompatibleRustVersions::Fallback;
                 } else {
                     self.gctx()
                         .shell()
                         .warn("ignoring `resolver` config table without `-Zmsrv-policy`")?;
                 }
             }
             Ok(CargoResolverConfig {
-                something_like_precedence: None,
+                incompatible_rust_versions: None,
             }) => {}
             Err(err) => {
                 if self.gctx().cli_unstable().msrv_policy {

src/cargo/util/context/mod.rs

@@ -2680,14 +2680,14 @@ impl BuildTargetConfig {
 #[derive(Debug, Deserialize)]
 #[serde(rename_all = "kebab-case")]
 pub struct CargoResolverConfig {
-    pub something_like_precedence: Option<CargoResolverPrecedence>,
+    pub incompatible_rust_versions: Option<IncompatibleRustVersions>,
 }
 
 #[derive(Debug, Deserialize, PartialEq, Eq)]
 #[serde(rename_all = "kebab-case")]
-pub enum CargoResolverPrecedence {
-    SomethingLikeMaximum,
-    SomethingLikeRustVersion,
+pub enum IncompatibleRustVersions {
+    Allow,
+    Fallback,
 }
 
 #[derive(Deserialize, Default)]

src/doc/src/reference/unstable.md

@@ -338,26 +338,27 @@ This was stabilized in 1.79 in [#13608](https://github.com/rust-lang/cargo/pull/
 ### MSRV-aware resolver
 
 `-Zmsrv-policy` allows access to an MSRV-aware resolver which can be enabled with:
-- `resolver.something-like-precedence` config field
+- `resolver.incompatible-rust-versions` config field
 - `workspace.resolver = "3"` / `package.resolver = "3"`
 - `package.edition = "2024"` (only in workspace root)
 
 The resolver will prefer dependencies with a `package.rust-version` that is the same or older than your project's MSRV.
 Your project's MSRV is determined by taking the lowest `package.rust-version` set among your workspace members.
 If there is none set, your toolchain version will be used with the intent to pick up the version from rustup's `rust-toolchain.toml`, if present.
 
-#### `resolver.something-like-precedence`
+#### `resolver.incompatible-rust-versions`
 * Type: string
-* Default: "something-like-maximum"
-* Environment: `CARGO_RESOLVER_SOMETHING_LIKE_PRECEDENCE`
+* Default: "allow"
+* Environment: `CARGO_RESOLVER_INCOMPATIBLE_RUST_VERSIONS`
 
-Select which policy should be used when resolving dependencies.  Values include
-- `something-like-maximum`: prefer highest compatible versions of a package
-- `something-like-rust-version`: prefer versions of packages compatible with your project's Rust version
+Select how packages with incompatible `package.rust-version`s are treated during dependency resolution.
+Values include:
+- `allow`: treat them like any other dependency
+- `fallback`: only consider them if no other dependency version matched
 
 Can be overridden with
 - `--ignore-rust-version` CLI option
-- Setting the dependency's version requirement too high
+- Setting the dependency's version requirement above any version with a compatible `package.rust-version`
 - Specifying the version to `cargo update` with `--precise`
 
 ## precise-pre-release

tests/testsuite/cargo_add/rust_version_ignore/mod.rs

@@ -25,10 +25,7 @@ fn case() {
         .arg("--ignore-rust-version")
         .arg_line("rust-version-user")
         .current_dir(cwd)
-        .env(
-            "CARGO_RESOLVER_SOMETHING_LIKE_PRECEDENCE",
-            "something-like-rust-version",
-        )
+        .env("CARGO_RESOLVER_INCOMPATIBLE_RUST_VERSIONS", "fallback")
         .masquerade_as_nightly_cargo(&["msrv-policy"])
         .assert()
         .code(0)

tests/testsuite/cargo_add/rust_version_incompatible/mod.rs

@@ -27,10 +27,7 @@ fn case() {
         .arg("add")
         .arg_line("rust-version-user")
         .current_dir(cwd)
-        .env(
-            "CARGO_RESOLVER_SOMETHING_LIKE_PRECEDENCE",
-            "something-like-rust-version",
-        )
+        .env("CARGO_RESOLVER_INCOMPATIBLE_RUST_VERSIONS", "fallback")
         .masquerade_as_nightly_cargo(&["msrv-policy"])
         .assert()
         .failure()

tests/testsuite/cargo_add/rust_version_latest/mod.rs

@@ -24,10 +24,7 @@ fn case() {
         .arg("add")
         .arg_line("rust-version-user")
         .current_dir(cwd)
-        .env(
-            "CARGO_RESOLVER_SOMETHING_LIKE_PRECEDENCE",
-            "something-like-rust-version",
-        )
+        .env("CARGO_RESOLVER_INCOMPATIBLE_RUST_VERSIONS", "fallback")
         .masquerade_as_nightly_cargo(&["msrv-policy"])
         .assert()
         .success()

tests/testsuite/cargo_add/rust_version_older/mod.rs

@@ -24,10 +24,7 @@ fn case() {
         .arg("add")
         .arg_line("rust-version-user")
         .current_dir(cwd)
-        .env(
-            "CARGO_RESOLVER_SOMETHING_LIKE_PRECEDENCE",
-            "something-like-rust-version",
-        )
+        .env("CARGO_RESOLVER_INCOMPATIBLE_RUST_VERSIONS", "fallback")
         .masquerade_as_nightly_cargo(&["msrv-policy"])
         .assert()
         .success()

tests/testsuite/cargo_add/rustc_ignore/mod.rs

@@ -28,10 +28,7 @@ fn case() {
         .arg("--ignore-rust-version")
         .arg_line("rust-version-user")
         .current_dir(cwd)
-        .env(
-            "CARGO_RESOLVER_SOMETHING_LIKE_PRECEDENCE",
-            "something-like-rust-version",
-        )
+        .env("CARGO_RESOLVER_INCOMPATIBLE_RUST_VERSIONS", "fallback")
         .masquerade_as_nightly_cargo(&["msrv-policy"])
         .assert()
         .code(0)

tests/testsuite/cargo_add/rustc_incompatible/mod.rs

@@ -21,10 +21,7 @@ fn case() {
         .arg("add")
         .arg_line("rust-version-user")
         .current_dir(cwd)
-        .env(
-            "CARGO_RESOLVER_SOMETHING_LIKE_PRECEDENCE",
-            "something-like-rust-version",
-        )
+        .env("CARGO_RESOLVER_INCOMPATIBLE_RUST_VERSIONS", "fallback")
         .masquerade_as_nightly_cargo(&["msrv-policy"])
         .assert()
         .failure()

tests/testsuite/cargo_add/rustc_latest/mod.rs

@@ -27,10 +27,7 @@ fn case() {
         .arg("add")
         .arg_line("rust-version-user")
         .current_dir(cwd)
-        .env(
-            "CARGO_RESOLVER_SOMETHING_LIKE_PRECEDENCE",
-            "something-like-rust-version",
-        )
+        .env("CARGO_RESOLVER_INCOMPATIBLE_RUST_VERSIONS", "fallback")
         .masquerade_as_nightly_cargo(&["msrv-policy"])
         .assert()
         .success()

tests/testsuite/cargo_add/rustc_older/mod.rs

@@ -27,10 +27,7 @@ fn case() {
         .arg("add")
         .arg_line("rust-version-user")
         .current_dir(cwd)
-        .env(
-            "CARGO_RESOLVER_SOMETHING_LIKE_PRECEDENCE",
-            "something-like-rust-version",
-        )
+        .env("CARGO_RESOLVER_INCOMPATIBLE_RUST_VERSIONS", "fallback")
         .masquerade_as_nightly_cargo(&["msrv-policy"])
         .assert()
         .success()