refactor(msrv): Simplify tracking of use of MSRV-aware resolver

The design for this stems from
- It being unclear what the initialization order would be
- Prematurely writing this for `Cargo.lock` version to leverage it and
  maybe to switch other MSRV-aware logic to

Author: epage

src/bin/cargo/commands/fix.rs

@@ -72,7 +72,7 @@ pub fn exec(gctx: &mut GlobalContext, args: &ArgMatches) -> CliResult {
     // code as we can.
     let root_manifest = args.root_manifest(gctx)?;
     let mut ws = Workspace::new(&root_manifest, gctx)?;
-    ws.set_honor_rust_version(args.honor_rust_version());
+    ws.set_resolve_honors_rust_version(args.honor_rust_version());
     let mut opts = args.compile_options(gctx, mode, Some(&ws), ProfileChecking::LegacyTestOnly)?;
 
     if !opts.filter.is_specific() {

src/cargo/core/workspace.rs

@@ -104,7 +104,6 @@ pub struct Workspace<'gctx> {
     /// The resolver behavior specified with the `resolver` field.
     resolve_behavior: ResolveBehavior,
     resolve_honors_rust_version: bool,
-    honor_rust_version: Option<bool>,
 
     /// Workspace-level custom metadata
     custom_metadata: Option<toml::Value>,
@@ -235,7 +234,6 @@ impl<'gctx> Workspace<'gctx> {
             ignore_lock: false,
             resolve_behavior: ResolveBehavior::V1,
             resolve_honors_rust_version: false,
-            honor_rust_version: None,
             custom_metadata: None,
         }
     }
@@ -649,18 +647,14 @@ impl<'gctx> Workspace<'gctx> {
         self.members().filter_map(|pkg| pkg.rust_version()).min()
     }
 
-    pub fn set_honor_rust_version(&mut self, honor_rust_version: Option<bool>) {
-        self.honor_rust_version = honor_rust_version;
-    }
-
-    pub fn honor_rust_version(&self) -> Option<bool> {
-        self.honor_rust_version
+    pub fn set_resolve_honors_rust_version(&mut self, honor_rust_version: Option<bool>) {
+        if let Some(honor_rust_version) = honor_rust_version {
+            self.resolve_honors_rust_version = honor_rust_version;
+        }
     }
 
     pub fn resolve_honors_rust_version(&self) -> bool {
-        // Give CLI precedence
-        self.honor_rust_version
-            .unwrap_or(self.resolve_honors_rust_version)
+        self.resolve_honors_rust_version
     }
 
     pub fn custom_metadata(&self) -> Option<&toml::Value> {

src/cargo/ops/fix.rs

@@ -108,7 +108,7 @@ pub fn fix(
         check_resolver_change(&original_ws, opts)?;
     }
     let mut ws = Workspace::new(&root_manifest, gctx)?;
-    ws.set_honor_rust_version(original_ws.honor_rust_version());
+    ws.set_resolve_honors_rust_version(Some(original_ws.resolve_honors_rust_version()));
 
     // Spin up our lock server, which our subprocesses will use to synchronize fixes.
     let lock_server = LockServer::new()?;

src/cargo/util/command_prelude.rs

@@ -505,7 +505,7 @@ pub trait ArgMatchesExt {
     fn workspace<'a>(&self, gctx: &'a GlobalContext) -> CargoResult<Workspace<'a>> {
         let root = self.root_manifest(gctx)?;
         let mut ws = Workspace::new(&root, gctx)?;
-        ws.set_honor_rust_version(self.honor_rust_version());
+        ws.set_resolve_honors_rust_version(self.honor_rust_version());
         if gctx.cli_unstable().avoid_dev_deps {
             ws.set_require_optional_deps(false);
         }