Rollup merge of #114959 - mojave2:issue-113702, r=petrochenkov

fix #113702 emit a proper diagnostic message for unstable lints passed from CLI

Current output:
```bash
$ build/host/stage1/bin/rustc hello.rs -Wunnameable_types
warning: unknown lint: `unnameable_types`
  |
  = note: the `unnameable_types` lint is unstable
  = note: see issue #48054 <https://github.com/rust-lang/rust/issues/48054> for more information
  = help: add `-Zcrate-attr="feature(type_privacy_lints)"` to the command-line options to enable
  = note: `#[warn(unknown_lints)]` on by default

warning: 1 warning emitted
```

Previously, the feature gate diagnostic message is like below, which is the same as the message for unstable lints from the root module.

```shell
= help: add `#![feature(type_privacy_lints)]` to the crate attributes to enable
```

Fixes https://github.com/rust-lang/rust/issues/113702

7 files changed, 46 insertions, 21 deletions

diff --git a/compiler/rustc_hir_analysis/src/check/mod.rs b/compiler/rustc_hir_analysis/src/check/mod.rs
index 4cf3587327d..d8331661366 100644
--- a/compiler/rustc_hir_analysis/src/check/mod.rs
+++ b/compiler/rustc_hir_analysis/src/check/mod.rs
@@ -289,6 +289,7 @@ fn default_body_is_unstable(
         &tcx.sess.parse_sess,
         feature,
         rustc_feature::GateIssue::Library(issue),
+        false,
     );
 
     err.emit();
diff --git a/compiler/rustc_lint/src/levels.rs b/compiler/rustc_lint/src/levels.rs
index 1f4e5fa4d3b..0a40d17f98e 100644
--- a/compiler/rustc_lint/src/levels.rs
+++ b/compiler/rustc_lint/src/levels.rs
@@ -12,7 +12,7 @@ use rustc_ast as ast;
 use rustc_ast_pretty::pprust;
 use rustc_data_structures::fx::FxHashMap;
 use rustc_errors::{DecorateLint, DiagnosticBuilder, DiagnosticMessage, MultiSpan};
-use rustc_feature::Features;
+use rustc_feature::{Features, GateIssue};
 use rustc_hir as hir;
 use rustc_hir::intravisit::{self, Visitor};
 use rustc_hir::HirId;
@@ -24,12 +24,14 @@ use rustc_middle::lint::{
 };
 use rustc_middle::query::Providers;
 use rustc_middle::ty::{RegisteredTools, TyCtxt};
-use rustc_session::lint::builtin::{RENAMED_AND_REMOVED_LINTS, UNKNOWN_LINTS, UNUSED_ATTRIBUTES};
 use rustc_session::lint::{
-    builtin::{self, FORBIDDEN_LINT_GROUPS, SINGLE_USE_LIFETIMES, UNFULFILLED_LINT_EXPECTATIONS},
+    builtin::{
+        self, FORBIDDEN_LINT_GROUPS, RENAMED_AND_REMOVED_LINTS, SINGLE_USE_LIFETIMES,
+        UNFULFILLED_LINT_EXPECTATIONS, UNKNOWN_LINTS, UNUSED_ATTRIBUTES,
+    },
     Level, Lint, LintExpectationId, LintId,
 };
-use rustc_session::parse::{add_feature_diagnostics, feature_err};
+use rustc_session::parse::feature_err;
 use rustc_session::Session;
 use rustc_span::symbol::{sym, Symbol};
 use rustc_span::{Span, DUMMY_SP};
@@ -566,7 +568,7 @@ impl<'s, P: LintLevelsProvider> LintLevelsBuilder<'s, P> {
                     continue;
                 }
 
-                if self.check_gated_lint(id, DUMMY_SP) {
+                if self.check_gated_lint(id, DUMMY_SP, true) {
                     let src = LintLevelSource::CommandLine(lint_flag_val, orig_level);
                     self.insert(id, (level, src));
                 }
@@ -837,7 +839,7 @@ impl<'s, P: LintLevelsProvider> LintLevelsBuilder<'s, P> {
                             reason,
                         };
                         for &id in *ids {
-                            if self.check_gated_lint(id, attr.span) {
+                            if self.check_gated_lint(id, attr.span, false) {
                                 self.insert_spec(id, (level, src));
                             }
                         }
@@ -854,7 +856,7 @@ impl<'s, P: LintLevelsProvider> LintLevelsBuilder<'s, P> {
                                     reason,
                                 };
                                 for &id in ids {
-                                    if self.check_gated_lint(id, attr.span) {
+                                    if self.check_gated_lint(id, attr.span, false) {
                                         self.insert_spec(id, (level, src));
                                     }
                                 }
@@ -955,7 +957,7 @@ impl<'s, P: LintLevelsProvider> LintLevelsBuilder<'s, P> {
                             reason,
                         };
                         for &id in ids {
-                            if self.check_gated_lint(id, attr.span) {
+                            if self.check_gated_lint(id, attr.span, false) {
                                 self.insert_spec(id, (level, src));
                             }
                         }
@@ -1000,7 +1002,7 @@ impl<'s, P: LintLevelsProvider> LintLevelsBuilder<'s, P> {
     // FIXME only emit this once for each attribute, instead of repeating it 4 times for
     // pre-expansion lints, post-expansion lints, `shallow_lint_levels_on` and `lint_expectations`.
     #[track_caller]
-    fn check_gated_lint(&self, lint_id: LintId, span: Span) -> bool {
+    fn check_gated_lint(&self, lint_id: LintId, span: Span, lint_from_cli: bool) -> bool {
         if let Some(feature) = lint_id.lint.feature_gate {
             if !self.features.enabled(feature) {
                 let lint = builtin::UNKNOWN_LINTS;
@@ -1015,7 +1017,13 @@ impl<'s, P: LintLevelsProvider> LintLevelsBuilder<'s, P> {
                     |lint| {
                         lint.set_arg("name", lint_id.lint.name_lower());
                         lint.note(fluent::lint_note);
-                        add_feature_diagnostics(lint, &self.sess.parse_sess, feature);
+                        rustc_session::parse::add_feature_diagnostics_for_issue(
+                            lint,
+                            &self.sess.parse_sess,
+                            feature,
+                            GateIssue::Language,
+                            lint_from_cli,
+                        );
                         lint
                     },
                 );
diff --git a/compiler/rustc_session/messages.ftl b/compiler/rustc_session/messages.ftl
index b07c6db599e..e06b6380944 100644
--- a/compiler/rustc_session/messages.ftl
+++ b/compiler/rustc_session/messages.ftl
@@ -8,6 +8,9 @@ session_cannot_mix_and_match_sanitizers = `-Zsanitizer={$first}` is incompatible
 session_cgu_not_recorded =
     CGU-reuse for `{$cgu_user_name}` is (mangled: `{$cgu_name}`) was not recorded
 
+session_cli_feature_diagnostic_help =
+    add `-Zcrate-attr="feature({$feature})"` to the command-line options to enable
+
 session_crate_name_does_not_match = `--crate-name` and `#[crate_name]` are required to match, but `{$s}` != `{$name}`
 
 session_crate_name_empty = crate name must not be empty
diff --git a/compiler/rustc_session/src/errors.rs b/compiler/rustc_session/src/errors.rs
index 78940462b2c..5f8bbfca890 100644
--- a/compiler/rustc_session/src/errors.rs
+++ b/compiler/rustc_session/src/errors.rs
@@ -57,6 +57,12 @@ pub struct FeatureDiagnosticHelp {
     pub feature: Symbol,
 }
 
+#[derive(Subdiagnostic)]
+#[help(session_cli_feature_diagnostic_help)]
+pub struct CliFeatureDiagnosticHelp {
+    pub feature: Symbol,
+}
+
 #[derive(Diagnostic)]
 #[diag(session_not_circumvent_feature)]
 pub struct NotCircumventFeature;
diff --git a/compiler/rustc_session/src/parse.rs b/compiler/rustc_session/src/parse.rs
index 1cf63e9b7ba..671204c0d8e 100644
--- a/compiler/rustc_session/src/parse.rs
+++ b/compiler/rustc_session/src/parse.rs
@@ -2,7 +2,9 @@
 //! It also serves as an input to the parser itself.
 
 use crate::config::CheckCfg;
-use crate::errors::{FeatureDiagnosticForIssue, FeatureDiagnosticHelp, FeatureGateError};
+use crate::errors::{
+    CliFeatureDiagnosticHelp, FeatureDiagnosticForIssue, FeatureDiagnosticHelp, FeatureGateError,
+};
 use crate::lint::{
     builtin::UNSTABLE_SYNTAX_PRE_EXPANSION, BufferedEarlyLint, BuiltinLintDiagnostics, Lint, LintId,
 };
@@ -110,7 +112,7 @@ pub fn feature_err_issue(
     }
 
     let mut err = sess.create_err(FeatureGateError { span, explain: explain.into() });
-    add_feature_diagnostics_for_issue(&mut err, sess, feature, issue);
+    add_feature_diagnostics_for_issue(&mut err, sess, feature, issue, false);
     err
 }
 
@@ -139,7 +141,7 @@ pub fn feature_warn_issue(
     explain: &'static str,
 ) {
     let mut err = sess.span_diagnostic.struct_span_warn(span, explain);
-    add_feature_diagnostics_for_issue(&mut err, sess, feature, issue);
+    add_feature_diagnostics_for_issue(&mut err, sess, feature, issue, false);
 
     // Decorate this as a future-incompatibility lint as in rustc_middle::lint::struct_lint_level
     let lint = UNSTABLE_SYNTAX_PRE_EXPANSION;
@@ -158,7 +160,7 @@ pub fn feature_warn_issue(
 
 /// Adds the diagnostics for a feature to an existing error.
 pub fn add_feature_diagnostics(err: &mut Diagnostic, sess: &ParseSess, feature: Symbol) {
-    add_feature_diagnostics_for_issue(err, sess, feature, GateIssue::Language);
+    add_feature_diagnostics_for_issue(err, sess, feature, GateIssue::Language, false);
 }
 
 /// Adds the diagnostics for a feature to an existing error.
@@ -171,6 +173,7 @@ pub fn add_feature_diagnostics_for_issue(
     sess: &ParseSess,
     feature: Symbol,
     issue: GateIssue,
+    feature_from_cli: bool,
 ) {
     if let Some(n) = find_feature_issue(feature, issue) {
         err.subdiagnostic(FeatureDiagnosticForIssue { n });
@@ -178,7 +181,11 @@ pub fn add_feature_diagnostics_for_issue(
 
     // #23973: do not suggest `#![feature(...)]` if we are in beta/stable
     if sess.unstable_features.is_nightly_build() {
-        err.subdiagnostic(FeatureDiagnosticHelp { feature });
+        if feature_from_cli {
+            err.subdiagnostic(CliFeatureDiagnosticHelp { feature });
+        } else {
+            err.subdiagnostic(FeatureDiagnosticHelp { feature });
+        }
     }
 }
 
diff --git a/tests/ui/unknown-unstable-lints/deny-unstable-lint-command-line.stderr b/tests/ui/unknown-unstable-lints/deny-unstable-lint-command-line.stderr
index aa73b824a57..32f8d2f45dc 100644
--- a/tests/ui/unknown-unstable-lints/deny-unstable-lint-command-line.stderr
+++ b/tests/ui/unknown-unstable-lints/deny-unstable-lint-command-line.stderr
@@ -1,18 +1,18 @@
 error: unknown lint: `test_unstable_lint`
    |
    = note: the `test_unstable_lint` lint is unstable
-   = help: add `#![feature(test_unstable_lint)]` to the crate attributes to enable
+   = help: add `-Zcrate-attr="feature(test_unstable_lint)"` to the command-line options to enable
    = note: requested on the command line with `-D unknown-lints`
 
 error: unknown lint: `test_unstable_lint`
    |
    = note: the `test_unstable_lint` lint is unstable
-   = help: add `#![feature(test_unstable_lint)]` to the crate attributes to enable
+   = help: add `-Zcrate-attr="feature(test_unstable_lint)"` to the command-line options to enable
 
 error: unknown lint: `test_unstable_lint`
    |
    = note: the `test_unstable_lint` lint is unstable
-   = help: add `#![feature(test_unstable_lint)]` to the crate attributes to enable
+   = help: add `-Zcrate-attr="feature(test_unstable_lint)"` to the command-line options to enable
 
 error: aborting due to 3 previous errors
 
diff --git a/tests/ui/unknown-unstable-lints/warn-unknown-unstable-lint-command-line.stderr b/tests/ui/unknown-unstable-lints/warn-unknown-unstable-lint-command-line.stderr
index 82851c80064..dd9ecf02fa6 100644
--- a/tests/ui/unknown-unstable-lints/warn-unknown-unstable-lint-command-line.stderr
+++ b/tests/ui/unknown-unstable-lints/warn-unknown-unstable-lint-command-line.stderr
@@ -1,18 +1,18 @@
 warning: unknown lint: `test_unstable_lint`
    |
    = note: the `test_unstable_lint` lint is unstable
-   = help: add `#![feature(test_unstable_lint)]` to the crate attributes to enable
+   = help: add `-Zcrate-attr="feature(test_unstable_lint)"` to the command-line options to enable
    = note: requested on the command line with `-W unknown-lints`
 
 warning: unknown lint: `test_unstable_lint`
    |
    = note: the `test_unstable_lint` lint is unstable
-   = help: add `#![feature(test_unstable_lint)]` to the crate attributes to enable
+   = help: add `-Zcrate-attr="feature(test_unstable_lint)"` to the command-line options to enable
 
 warning: unknown lint: `test_unstable_lint`
    |
    = note: the `test_unstable_lint` lint is unstable
-   = help: add `#![feature(test_unstable_lint)]` to the crate attributes to enable
+   = help: add `-Zcrate-attr="feature(test_unstable_lint)"` to the command-line options to enable
 
 warning: 3 warnings emitted