Auto merge of #13505 - epage:edition-warn, r=weihanglo

feat(toml): Warn on unset Edition

### What does this PR try to resolve?

On [Internals](https://internals.rust-lang.org/t/idea-rustc-cargo-should-warn-on-unspecified-edition/20309), the idea came up for warning on unset Edition.

Besides helping people who forget to set the Edition, this creates symmetry between `Cargo.toml` and cargo scripts (#12207).  While the default is different in each case, we are making the default obvious and guiding people away from it.

### How should we test and review this PR?

There are separate commits for adding tests (and refactors) so the changes in behavior will be more obvious

### Additional information

This builds on
- #13499
- #13504

src/cargo/core/features.rs

@@ -180,9 +180,12 @@ pub type AllowFeatures = BTreeSet<String>;
 /// [`is_stable`]: Edition::is_stable
 /// [`toml::to_real_manifest`]: crate::util::toml::to_real_manifest
 /// [`features!`]: macro.features.html
-#[derive(Clone, Copy, Debug, Hash, PartialOrd, Ord, Eq, PartialEq, Serialize, Deserialize)]
+#[derive(
+ Default, Clone, Copy, Debug, Hash, PartialOrd, Ord, Eq, PartialEq, Serialize, Deserialize,
+)]
 pub enum Edition {
  /// The 2015 edition
+ #[default]
  Edition2015,
  /// The 2018 edition
  Edition2018,
@@ -199,6 +202,12 @@ impl Edition {
  pub const LATEST_UNSTABLE: Option<Edition> = Some(Edition::Edition2024);
  /// The latest stable edition.
  pub const LATEST_STABLE: Edition = Edition::Edition2021;
+ pub const ALL: &'static [Edition] = &[
+ Self::Edition2015,
+ Self::Edition2018,
+ Self::Edition2021,
+ Self::Edition2024,
+ ];
  /// Possible values allowed for the `--edition` CLI flag.
  ///
  /// This requires a static value due to the way clap works, otherwise I

src/cargo/util/toml/mod.rs

@@ -9,6 +9,7 @@ use crate::AlreadyPrintedError;
 use anyhow::{anyhow, bail, Context as _};
 use cargo_platform::Platform;
 use cargo_util::paths;
+use cargo_util_schemas::core::PartialVersion;
 use cargo_util_schemas::manifest;
 use cargo_util_schemas::manifest::RustVersion;
 use itertools::Itertools;
@@ -563,14 +564,69 @@ pub fn to_real_manifest(
  source_id,
  );
 
+ let rust_version = if let Some(rust_version) = &package.rust_version {
+ let rust_version = field_inherit_with(rust_version.clone(), "rust_version", || {
+ inherit()?.rust_version()
+ })?;
+ Some(rust_version)
+ } else {
+ None
+ };
+
  let edition = if let Some(edition) = package.edition.clone() {
  let edition: Edition = field_inherit_with(edition, "edition", || inherit()?.edition())?
  .parse()
  .with_context(|| "failed to parse the `edition` key")?;
  package.edition = Some(manifest::InheritableField::Value(edition.to_string()));
+ if let Some(rust_version) = &rust_version {
+ let req = rust_version.to_caret_req();
+ if let Some(first_version) = edition.first_version() {
+ let unsupported =
+ semver::Version::new(first_version.major, first_version.minor - 1, 9999);
+ if req.matches(&unsupported) {
+ bail!(
+ "rust-version {} is older than first version ({}) required by \
+ the specified edition ({})",
+ rust_version,
+ first_version,
+ edition,
+ )
+ }
+ }
+ }
  edition
  } else {
- Edition::Edition2015
+ let msrv_edition = if let Some(rust_version) = &rust_version {
+ Edition::ALL
+ .iter()
+ .filter(|e| {
+ e.first_version()
+ .map(|e| {
+ let e = PartialVersion::from(e);
+ e <= **rust_version
+ })
+ .unwrap_or_default()
+ })
+ .max()
+ .copied()
+ } else {
+ None
+ }
+ .unwrap_or_default();
+ let default_edition = Edition::default();
+ let latest_edition = Edition::LATEST_STABLE;
+
+ let tip = if msrv_edition == default_edition {
+ String::new()
+ } else if msrv_edition == latest_edition {
+ format!(" while the latest is {latest_edition}")
+ } else {
+ format!(" while {msrv_edition} is compatible with `rust-version`")
+ };
+ warnings.push(format!(
+ "no edition set: defaulting to the {default_edition} edition{tip}",
+ ));
+ default_edition
  };
  // Add these lines if start a new unstable edition.
  // ```
@@ -588,29 +644,6 @@ pub fn to_real_manifest(
  )));
  }
 
- let rust_version = if let Some(rust_version) = &package.rust_version {
- let rust_version = field_inherit_with(rust_version.clone(), "rust_version", || {
- inherit()?.rust_version()
- })?;
- let req = rust_version.to_caret_req();
- if let Some(first_version) = edition.first_version() {
- let unsupported =
- semver::Version::new(first_version.major, first_version.minor - 1, 9999);
- if req.matches(&unsupported) {
- bail!(
- "rust-version {} is older than first version ({}) required by \
- the specified edition ({})",
- rust_version,
- first_version,
- edition,
- )
- }
- }
- Some(rust_version)
- } else {
- None
- };
-
  if package.metabuild.is_some() {
  features.require(Feature::metabuild())?;
  }

tests/testsuite/bench.rs

@@ -331,6 +331,7 @@ fn bench_with_lib_dep() {
  [package]
  name = "foo"
  version = "0.0.1"
+ edition = "2015"
  authors = []
 
  [[bin]]
@@ -396,6 +397,7 @@ fn bench_with_deep_lib_dep() {
  [package]
  name = "bar"
  version = "0.0.1"
+ edition = "2015"
  authors = []
 
  [dependencies.foo]
@@ -454,6 +456,7 @@ fn external_bench_explicit() {
  [package]
  name = "foo"
  version = "0.0.1"
+ edition = "2015"
  authors = []
 
  [[bench]]
@@ -697,6 +700,7 @@ fn lib_bin_same_name() {
  [package]
  name = "foo"
  version = "0.0.1"
+ edition = "2015"
  authors = []
 
  [lib]
@@ -796,6 +800,7 @@ fn lib_with_standard_name2() {
  [package]
  name = "syntax"
  version = "0.0.1"
+ edition = "2015"
  authors = []
 
  [lib]
@@ -842,6 +847,7 @@ fn bench_dylib() {
  [package]
  name = "foo"
  version = "0.0.1"
+ edition = "2015"
  authors = []
 
  [lib]
@@ -883,6 +889,7 @@ fn bench_dylib() {
  [package]
  name = "bar"
  version = "0.0.1"
+ edition = "2015"
  authors = []
 
  [lib]
@@ -932,6 +939,7 @@ fn bench_twice_with_build_cmd() {
  [package]
  name = "foo"
  version = "0.0.1"
+ edition = "2015"
  authors = []
  build = "build.rs"
  "#,
@@ -977,6 +985,7 @@ fn bench_with_examples() {
  [package]
  name = "foo"
  version = "6.6.6"
+ edition = "2015"
  authors = []
 
  [[example]]
@@ -1061,6 +1070,7 @@ fn test_a_bench() {
  name = "foo"
  authors = []
  version = "0.1.0"
+ edition = "2015"
 
  [lib]
  name = "foo"
@@ -1219,6 +1229,7 @@ fn test_bench_multiple_packages() {
  name = "foo"
  authors = []
  version = "0.1.0"
+ edition = "2015"
 
  [dependencies.bar]
  path = "../bar"
@@ -1239,6 +1250,7 @@ fn test_bench_multiple_packages() {
  name = "bar"
  authors = []
  version = "0.1.0"
+ edition = "2015"
 
  [[bench]]
  name = "bbar"
@@ -1269,6 +1281,7 @@ fn test_bench_multiple_packages() {
  name = "baz"
  authors = []
  version = "0.1.0"
+ edition = "2015"
 
  [[bench]]
  name = "bbaz"
@@ -1307,6 +1320,7 @@ fn bench_all_workspace() {
  [package]
  name = "foo"
  version = "0.1.0"
+ edition = "2015"
 
  [dependencies]
  bar = { path = "bar" }
@@ -1360,6 +1374,7 @@ fn bench_all_exclude() {
  [package]
  name = "foo"
  version = "0.1.0"
+ edition = "2015"
 
  [workspace]
  members = ["bar", "baz"]
@@ -1405,6 +1420,7 @@ fn bench_all_exclude_glob() {
  [package]
  name = "foo"
  version = "0.1.0"
+ edition = "2015"
 
  [workspace]
  members = ["bar", "baz"]
@@ -1549,6 +1565,7 @@ fn legacy_bench_name() {
  [package]
  name = "foo"
  version = "0.1.0"
+ edition = "2015"
 
  [[bench]]
  name = "bench"