Specify MSRV

And test that we accurately test it

Cargo.toml

@@ -1,5 +1,5 @@
 [workspace]
-members = ["num_enum", "num_enum_derive", "renamed_num_enum", "serde_example", "stress_tests"]
+members = ["metadata_checks", "num_enum", "num_enum_derive", "renamed_num_enum", "serde_example", "stress_tests"]
 # Exclude num_enum_derive because its useful doc comments import num_enum, which the crate doesn't do (because it would
 # cause a circular dependency), so the doc tests don't actually compile.
 default-members  = ["num_enum", "renamed_num_enum", "serde_example", "stress_tests"]

metadata_checks/Cargo.toml

@@ -0,0 +1,10 @@
+[package]
+name = "metadata_check"
+version = "0.1.0"
+edition = "2018"
+publish = false
+
+[dev-dependencies]
+cargo_toml = "0.13.3"
+serde = "1"
+serde_yaml = "0.9"

metadata_checks/tests/metadata_checks.rs

@@ -0,0 +1,117 @@
+use cargo_toml::Manifest;
+use std::collections::{BTreeMap, BTreeSet};
+use std::path::PathBuf;
+
+#[test]
+fn msrv() {
+    let workspace_root = get_workspace_root();
+
+    let crates_to_msrvs: BTreeMap<String, String> = vec!["num_enum", "num_enum_derive"]
+        .into_iter()
+        .map(|crate_name| {
+            let manifest_path = workspace_root.join(crate_name).join("Cargo.toml");
+            (
+                crate_name.to_owned(),
+                Manifest::from_path(&manifest_path)
+                    .map_err(|err| {
+                        format!(
+                            "Failed to read manifest from path {:?}: {:?}",
+                            manifest_path, err
+                        )
+                    })
+                    .unwrap()
+                    .package
+                    .ok_or_else(|| format!("Missing package for crate {:?}", crate_name))
+                    .unwrap()
+                    .rust_version()
+                    .ok_or_else(|| format!("Missing rust-version for crate {:?}", crate_name))
+                    .unwrap()
+                    .to_owned(),
+            )
+        })
+        .collect();
+
+    let crates_msrvs: BTreeSet<_> = crates_to_msrvs.values().cloned().collect();
+    if crates_msrvs.len() != 1 {
+        panic!(
+            "Want exactly one MSRV across crates, but found: {:?}",
+            crates_to_msrvs
+        );
+    }
+
+    let action_bytes = std::fs::read(
+        workspace_root
+            .join(".github")
+            .join("workflows")
+            .join("msrv-build.yml"),
+    )
+    .expect("Failed to read github workflows yaml");
+    let action_file: github_action::File = serde_yaml::from_slice(&action_bytes).unwrap();
+
+    let toolchains: BTreeSet<String> = action_file
+        .jobs
+        .values()
+        .flat_map(|v| v.steps.iter())
+        .filter_map(|step| step.with.as_ref())
+        .map(|step_with| step_with.toolchain.clone())
+        .collect();
+
+    assert_eq!(toolchains, crates_msrvs);
+}
+
+#[test]
+fn dep_version() {
+    let workspace_root = get_workspace_root();
+    let num_enum_manifest =
+        Manifest::from_path(workspace_root.join("num_enum").join("Cargo.toml")).unwrap();
+    let num_enum_derive_manifest =
+        Manifest::from_path(workspace_root.join("num_enum_derive").join("Cargo.toml")).unwrap();
+
+    let requested_dependency_version = num_enum_manifest
+        .dependencies
+        .get("num_enum_derive")
+        .unwrap()
+        .detail()
+        .unwrap()
+        .version
+        .clone()
+        .unwrap();
+    let num_enum_derive_version = num_enum_derive_manifest.package.unwrap().version.unwrap();
+
+    let expected_dependency_version = format!("={}", num_enum_derive_version);
+
+    assert_eq!(expected_dependency_version, requested_dependency_version);
+}
+
+fn get_workspace_root() -> PathBuf {
+    PathBuf::from(std::env::var_os("CARGO_MANIFEST_DIR").unwrap())
+        .parent()
+        .unwrap()
+        .to_path_buf()
+}
+
+mod github_action {
+    use serde::Deserialize;
+    use std::collections::BTreeMap;
+
+    #[derive(Deserialize)]
+    pub struct File {
+        pub jobs: BTreeMap<String, Job>,
+    }
+
+    #[derive(Deserialize)]
+    pub struct Job {
+        pub steps: Vec<Step>,
+    }
+
+    #[derive(Deserialize)]
+    pub struct Step {
+        pub uses: Option<String>,
+        pub with: Option<With>,
+    }
+
+    #[derive(Deserialize)]
+    pub struct With {
+        pub toolchain: String,
+    }
+}

num_enum/Cargo.toml

@@ -1,6 +1,7 @@
 [package]
 name = "num_enum"
 version = "0.6.0"  # Keep in sync with num_enum_derive, the the dependency on it below.
+rust-version = "1.56.0"
 authors = [
   "Daniel Wagner-Hall <dawagner@gmail.com>",
   "Daniel Henry-Mantilla <daniel.henry.mantilla@gmail.com>",

num_enum_derive/Cargo.toml

@@ -1,6 +1,7 @@
 [package]
 name = "num_enum_derive"
 version = "0.6.0"  # Keep in sync with num_enum.
+rust-version = "1.56.0"
 authors = [
   "Daniel Wagner-Hall <dawagner@gmail.com>",
   "Daniel Henry-Mantilla <daniel.henry.mantilla@gmail.com>",