Add --ignore-rust-version flag to cargo add

src/bin/cargo/commands/add.rs

@@ -72,6 +72,10 @@ The package will be removed from your features.")
 Example uses:
 - Depending on multiple versions of a crate
 - Depend on crates with the same name from different registries"),
+            flag(
+                "ignore-rust-version",
+                "Ignore `rust-version` specification in packages (unstable)"
+            ),
         ])
         .arg_manifest_path()
         .arg_package("Package to modify")
@@ -188,12 +192,23 @@ pub fn exec(config: &mut Config, args: &ArgMatches) -> CliResult {
 
     let dependencies = parse_dependencies(config, args)?;
 
+    let honor_rust_version = !args.flag("ignore-rust-version");
+    if !config.cli_unstable().msrv_policy && !honor_rust_version {
+        return Err(CliError::new(
+            anyhow::format_err!(
+                "the `ignore-rust-version` flag is unstable, pass -Z msrv-policy to enable it"
+            ),
+            101,
+        ));
+    }
+
     let options = AddOptions {
         config,
         spec,
         dependencies,
         section,
         dry_run,
+        honor_rust_version,
     };
     add(&ws, &options)?;
 

src/cargo/ops/cargo_add/mod.rs

@@ -51,6 +51,8 @@ pub struct AddOptions<'a> {
     pub section: DepTable,
     /// Act as if dependencies will be added
     pub dry_run: bool,
+    /// Whether the minimum supported Rust version should be considered during resolution
+    pub honor_rust_version: bool,
 }
 
 /// Add dependencies to a manifest
@@ -88,6 +90,7 @@ pub fn add(workspace: &Workspace<'_>, options: &AddOptions<'_>) -> CargoResult<(
                     workspace,
                     &options.spec,
                     &options.section,
+                    options.honor_rust_version,
                     options.config,
                     &mut registry,
                 )
@@ -259,6 +262,7 @@ fn resolve_dependency(
     ws: &Workspace<'_>,
     spec: &Package,
     section: &DepTable,
+    honor_rust_version: bool,
     config: &Config,
     registry: &mut PackageRegistry<'_>,
 ) -> CargoResult<DependencyUI> {
@@ -370,7 +374,14 @@ fn resolve_dependency(
             }
             dependency = dependency.set_source(src);
         } else {
-            let latest = get_latest_dependency(spec, &dependency, false, config, registry)?;
+            let latest = get_latest_dependency(
+                spec,
+                &dependency,
+                false,
+                honor_rust_version,
+                config,
+                registry,
+            )?;
 
             if dependency.name != latest.name {
                 config.shell().warn(format!(
@@ -523,6 +534,7 @@ fn get_latest_dependency(
     spec: &Package,
     dependency: &Dependency,
     _flag_allow_prerelease: bool,
+    honor_rust_version: bool,
     config: &Config,
     registry: &mut PackageRegistry<'_>,
 ) -> CargoResult<Dependency> {
@@ -554,7 +566,7 @@ fn get_latest_dependency(
                 )
             })?;
 
-            if config.cli_unstable().msrv_policy {
+            if config.cli_unstable().msrv_policy && honor_rust_version {
                 if let Some((req_major, req_minor, req_patch)) =
                     spec.rust_version().map(parse_rust_version)
                 {
@@ -584,7 +596,8 @@ fn get_latest_dependency(
                         .ok_or_else(|| {
                             let mut error_msg = format!(
                                 "could not find version of crate `{dependency}` that satisfies \
-                                 this package's rust-version"
+                                 this package's rust-version\n\
+                                 help: use `--ignore-rust-version` to override this behavior"
                             );
 
                             if let Some((lowest, _)) = rust_versions
@@ -605,7 +618,7 @@ fn get_latest_dependency(
                     if latest_msrv.version() < latest.version() {
                         config.shell().warn(format_args!(
                             "selecting older version of `{dependency}` to satisfy this package's \
-                             rust-version"
+                             rust-version (use `--ignore-rust-version` to override)"
                         ))?;
                         latest = latest_msrv;
                     }