fix(install): Don't respect MSRV for non-local installs

This is part of #9930

Author: epage

src/cargo/core/workspace.rs

@@ -657,6 +657,10 @@ impl<'gctx> Workspace<'gctx> {
         self.honor_rust_version
     }
 
+    pub fn set_resolve_honors_rust_version(&mut self, honor_rust_version: Option<bool>) {
+        self.resolve_honors_rust_version = honor_rust_version;
+    }
+
     pub fn resolve_honors_rust_version(&self) -> bool {
         // Give CLI precedence
         self.honor_rust_version

src/cargo/ops/cargo_install.rs

@@ -819,7 +819,9 @@ fn make_ws_rustc_target<'gctx>(
     let mut ws = if source_id.is_git() || source_id.is_path() {
         Workspace::new(pkg.manifest_path(), gctx)?
     } else {
-        Workspace::ephemeral(pkg, gctx, None, false)?
+        let mut ws = Workspace::ephemeral(pkg, gctx, None, false)?;
+        ws.set_resolve_honors_rust_version(Some(false));
+        ws
     };
     ws.set_ignore_lock(gctx.lock_update_allowed());
     ws.set_require_optional_deps(false);

tests/testsuite/rust_version.rs

@@ -1146,11 +1146,10 @@ fn cargo_install_ignores_msrv_config() {
 [DOWNLOADING] crates ...
 [DOWNLOADED] foo v0.0.1 (registry [..])
 [INSTALLING] foo v0.0.1
-[LOCKING] 2 packages to latest Rust 1.60 compatible versions
-[ADDING] dep v1.0.0 (latest: v1.1.0)
+[LOCKING] 2 packages to latest compatible versions
 [DOWNLOADING] crates ...
-[DOWNLOADED] dep v1.0.0 (registry [..])
-[COMPILING] dep v1.0.0
+[DOWNLOADED] dep v1.1.0 (registry [..])
+[COMPILING] dep v1.1.0
 [COMPILING] foo v0.0.1
 [FINISHED] `release` profile [optimized] target(s) in [..]
 [INSTALLING] [CWD]/home/.cargo/bin/foo[EXE]