From a8e816b079ff5515d04cd7ea3789747f5f347e66 Mon Sep 17 00:00:00 2001
From: Ed Page <eopage@gmail.com>
Date: Thu, 11 Apr 2024 14:36:50 -0500
Subject: [PATCH 1/3] test(resolve): Show no-MSRV case

---
 tests/testsuite/rust_version.rs | 49 +++++++++++++++++++++++++++++++++
 1 file changed, 49 insertions(+)

diff --git a/tests/testsuite/rust_version.rs b/tests/testsuite/rust_version.rs
index 6ed36dab9..8454d3f40 100644
--- a/tests/testsuite/rust_version.rs
+++ b/tests/testsuite/rust_version.rs
@@ -370,6 +370,55 @@ fn dependency_rust_version_older_and_newer_than_package() {
         .run();
 }
 
+#[cargo_test]
+fn resolve_with_rustc() {
+    Package::new("bar", "1.5.0")
+        .rust_version("1.0")
+        .file("src/lib.rs", "fn other_stuff() {}")
+        .publish();
+    Package::new("bar", "1.6.0")
+        .rust_version("1.2345")
+        .file("src/lib.rs", "fn other_stuff() {}")
+        .publish();
+
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+            [package]
+            name = "foo"
+            version = "0.0.1"
+            edition = "2015"
+            authors = []
+            [dependencies]
+            bar = "1.0.0"
+        "#,
+        )
+        .file("src/main.rs", "fn main(){}")
+        .build();
+
+    p.cargo("generate-lockfile --ignore-rust-version")
+        .arg("-Zmsrv-policy")
+        .masquerade_as_nightly_cargo(&["msrv-policy"])
+        .with_stderr(
+            "\
+[UPDATING] `dummy-registry` index
+[LOCKING] 2 packages
+",
+        )
+        .run();
+    p.cargo("generate-lockfile")
+        .arg("-Zmsrv-policy")
+        .masquerade_as_nightly_cargo(&["msrv-policy"])
+        .with_stderr(
+            "\
+[UPDATING] `dummy-registry` index
+[LOCKING] 2 packages
+",
+        )
+        .run();
+}
+
 #[cargo_test]
 fn dependency_rust_version_backtracking() {
     Package::new("has-rust-version", "1.6.0")

From b7b3874d097fd262d49eb65f52c1bb6ea9975dd8 Mon Sep 17 00:00:00 2001
From: Ed Page <eopage@gmail.com>
Date: Thu, 11 Apr 2024 14:38:02 -0500
Subject: [PATCH 2/3] refactor(resolve): Make it easier to extend MSRV logic

---
 src/cargo/ops/resolve.rs | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/cargo/ops/resolve.rs b/src/cargo/ops/resolve.rs
index e9af9f975..bedca23be 100644
--- a/src/cargo/ops/resolve.rs
+++ b/src/cargo/ops/resolve.rs
@@ -304,7 +304,8 @@ pub fn resolve_with_previous<'gctx>(
         version_prefs.version_ordering(VersionOrdering::MinimumVersionsFirst)
     }
     if ws.resolve_honors_rust_version() {
-        version_prefs.max_rust_version(ws.rust_version().cloned().map(RustVersion::into_partial));
+        let rust_version = ws.rust_version().cloned().map(RustVersion::into_partial);
+        version_prefs.max_rust_version(rust_version);
     }
 
     let avoid_patch_ids = if register_patches {

From 38718eaa936b82919d988aa6cc617ed83c4b5528 Mon Sep 17 00:00:00 2001
From: Ed Page <eopage@gmail.com>
Date: Thu, 11 Apr 2024 14:40:52 -0500
Subject: [PATCH 3/3] feat(resolve): Fallback to 'rustc -V' for MSRV resolving

---
 src/cargo/ops/resolve.rs        | 11 ++++++++---
 tests/testsuite/rust_version.rs |  1 +
 2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/src/cargo/ops/resolve.rs b/src/cargo/ops/resolve.rs
index bedca23be..41aef8664 100644
--- a/src/cargo/ops/resolve.rs
+++ b/src/cargo/ops/resolve.rs
@@ -73,7 +73,6 @@ use crate::util::cache_lock::CacheLockMode;
 use crate::util::errors::CargoResult;
 use crate::util::CanonicalUrl;
 use anyhow::Context as _;
-use cargo_util_schemas::manifest::RustVersion;
 use std::collections::{HashMap, HashSet};
 use tracing::{debug, trace};
 
@@ -304,8 +303,14 @@ pub fn resolve_with_previous<'gctx>(
         version_prefs.version_ordering(VersionOrdering::MinimumVersionsFirst)
     }
     if ws.resolve_honors_rust_version() {
-        let rust_version = ws.rust_version().cloned().map(RustVersion::into_partial);
-        version_prefs.max_rust_version(rust_version);
+        let rust_version = if let Some(ver) = ws.rust_version() {
+            ver.clone().into_partial()
+        } else {
+            let rustc = ws.gctx().load_global_rustc(Some(ws))?;
+            let rustc_version = rustc.version.clone().into();
+            rustc_version
+        };
+        version_prefs.max_rust_version(Some(rust_version));
     }
 
     let avoid_patch_ids = if register_patches {
diff --git a/tests/testsuite/rust_version.rs b/tests/testsuite/rust_version.rs
index 8454d3f40..d6e49091e 100644
--- a/tests/testsuite/rust_version.rs
+++ b/tests/testsuite/rust_version.rs
@@ -414,6 +414,7 @@ fn resolve_with_rustc() {
             "\
 [UPDATING] `dummy-registry` index
 [LOCKING] 2 packages
+[ADDING] bar v1.5.0 (latest: v1.6.0)
 ",
         )
         .run();