Auto merge of #9588 - ehuss:edition2021-force-warns, r=alexcrichton

Enable support for fix --edition for 2021.

This adds support for using `cargo fix --edition` to migrate to 2021.

This also uses the new, currently unstable, `--force-warns` flag. This was added because there were a significant number of crates that were "allow"ing lints that are required for migrating the edition. This wasn't a problem for 2018, because its lints were new, and all "allow" to start.  For 2021, several older "warn" lints are becoming hard errors.  "allow"ing them would cause the migration to fail.

src/cargo/core/features.rs

@@ -208,15 +208,15 @@ impl Edition {
 
     /// Whether or not this edition supports the `rust_*_compatibility` lint.
     ///
-    /// Ideally this would not be necessary, but currently 2021 does not have
-    /// any lints, and thus `rustc` doesn't recognize it. Perhaps `rustc`
-    /// could create an empty group instead?
+    /// Ideally this would not be necessary, but editions may not have any
+    /// lints, and thus `rustc` doesn't recognize it. Perhaps `rustc` could
+    /// create an empty group instead?
     pub(crate) fn supports_compat_lint(&self) -> bool {
         use Edition::*;
         match self {
             Edition2015 => false,
             Edition2018 => true,
-            Edition2021 => false,
+            Edition2021 => true,
         }
     }
 

src/cargo/ops/fix.rs

@@ -330,7 +330,7 @@ pub fn fix_maybe_exec_rustc(config: &Config) -> CargoResult<bool> {
     // that we have to back it all out.
     if !fixes.files.is_empty() {
         let mut cmd = rustc.build_command();
-        args.apply(&mut cmd);
+        args.apply(&mut cmd, config);
         cmd.arg("--error-format=json");
         let output = cmd.output().context("failed to spawn rustc")?;
 
@@ -369,7 +369,7 @@ pub fn fix_maybe_exec_rustc(config: &Config) -> CargoResult<bool> {
     // - If `--broken-code`, show the error messages.
     // - If the fix succeeded, show any remaining warnings.
     let mut cmd = rustc.build_command();
-    args.apply(&mut cmd);
+    args.apply(&mut cmd, config);
     for arg in args.format_args {
         // Add any json/error format arguments that Cargo wants. This allows
         // things like colored output to work correctly.
@@ -457,7 +457,7 @@ fn rustfix_crate(
             // We'll generate new errors below.
             file.errors_applying_fixes.clear();
         }
-        rustfix_and_fix(&mut fixes, rustc, filename, args)?;
+        rustfix_and_fix(&mut fixes, rustc, filename, args, config)?;
         let mut progress_yet_to_be_made = false;
         for (path, file) in fixes.files.iter_mut() {
             if file.errors_applying_fixes.is_empty() {
@@ -499,14 +499,15 @@ fn rustfix_and_fix(
     rustc: &ProcessBuilder,
     filename: &Path,
     args: &FixArgs,
+    config: &Config,
 ) -> Result<(), Error> {
     // If not empty, filter by these lints.
     // TODO: implement a way to specify this.
     let only = HashSet::new();
 
     let mut cmd = rustc.build_command();
     cmd.arg("--error-format=json");
-    args.apply(&mut cmd);
+    args.apply(&mut cmd, config);
     let output = cmd.output().with_context(|| {
         format!(
             "failed to execute `{}`",
@@ -763,7 +764,7 @@ impl FixArgs {
         })
     }
 
-    fn apply(&self, cmd: &mut Command) {
+    fn apply(&self, cmd: &mut Command, config: &Config) {
         cmd.arg(&self.file);
         cmd.args(&self.other).arg("--cap-lints=warn");
         if let Some(edition) = self.enabled_edition {
@@ -775,7 +776,13 @@ impl FixArgs {
 
         if let Some(edition) = self.prepare_for_edition {
             if edition.supports_compat_lint() {
-                cmd.arg("-W").arg(format!("rust-{}-compatibility", edition));
+                if config.nightly_features_allowed {
+                    cmd.arg("--force-warns")
+                        .arg(format!("rust-{}-compatibility", edition))
+                        .arg("-Zunstable-options");
+                } else {
+                    cmd.arg("-W").arg(format!("rust-{}-compatibility", edition));
+                }
             }
         }
     }

tests/testsuite/fix.rs

@@ -1501,3 +1501,49 @@ fn rustfix_handles_multi_spans() {
     p.cargo("fix --allow-no-vcs").run();
     assert!(p.read_file("src/lib.rs").contains(r#"panic!("hey");"#));
 }
+
+#[cargo_test]
+fn fix_edition_2021() {
+    // Can migrate 2021, even when lints are allowed.
+    if !is_nightly() {
+        // 2021 is unstable
+        return;
+    }
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+                [package]
+                name = "foo"
+                version = "0.1.0"
+                edition = "2018"
+            "#,
+        )
+        .file(
+            "src/lib.rs",
+            r#"
+                #![allow(ellipsis_inclusive_range_patterns)]
+
+                pub fn f() -> bool {
+                    let x = 123;
+                    match x {
+                        0...100 => true,
+                        _ => false,
+                    }
+                }
+            "#,
+        )
+        .build();
+    p.cargo("fix --edition --allow-no-vcs")
+        .masquerade_as_nightly_cargo()
+        .with_stderr(
+            "\
+[CHECKING] foo v0.1.0 [..]
+[MIGRATING] src/lib.rs from 2018 edition to 2021
+[FIXED] src/lib.rs (1 fix)
+[FINISHED] [..]
+",
+        )
+        .run();
+    assert!(p.read_file("src/lib.rs").contains(r#"0..=100 => true,"#));
+}