Auto merge of #85788 - rylev:force-warns, r=nikomatsakis

Support for force-warns

Implements #85512.

This PR adds a new command line option `force-warns` which will force the provided lints to warn even if they are allowed by some other mechanism such as `#![allow(warnings)]`.

Some remaining issues:
* #85512 mentions that `force-warns` should also be capable of taking lint groups instead of individual lints. This is not implemented.
* If a lint has a higher warning level than `warn`, this will cause that lint to warn instead. We probably want to allow the lint to error if it is set to a higher lint and is not allowed somewhere else.
* One test is currently ignored because it's not working - when a deny-by-default lint is allowed, it does not currently warn under `force-warns`. I'm not sure why, but I wanted to get this in before the weekend.

r? `@nikomatsakis`

compiler/rustc_lint/src/context.rs

@@ -334,8 +334,14 @@ impl LintStore {
         }
     }
 
-    /// Checks the validity of lint names derived from the command line
-    pub fn check_lint_name_cmdline(&self, sess: &Session, lint_name: &str, level: Level) {
+    /// Checks the validity of lint names derived from the command line. Returns
+    /// true if the lint is valid, false otherwise.
+    pub fn check_lint_name_cmdline(
+        &self,
+        sess: &Session,
+        lint_name: &str,
+        level: Option<Level>,
+    ) -> bool {
         let db = match self.check_lint_name(lint_name, None) {
             CheckLintNameResult::Ok(_) => None,
             CheckLintNameResult::Warning(ref msg, _) => Some(sess.struct_warn(msg)),
@@ -361,18 +367,23 @@ impl LintStore {
         };
 
         if let Some(mut db) = db {
-            let msg = format!(
-                "requested on the command line with `{} {}`",
-                match level {
-                    Level::Allow => "-A",
-                    Level::Warn => "-W",
-                    Level::Deny => "-D",
-                    Level::Forbid => "-F",
-                },
-                lint_name
-            );
-            db.note(&msg);
+            if let Some(level) = level {
+                let msg = format!(
+                    "requested on the command line with `{} {}`",
+                    match level {
+                        Level::Allow => "-A",
+                        Level::Warn => "-W",
+                        Level::Deny => "-D",
+                        Level::Forbid => "-F",
+                    },
+                    lint_name
+                );
+                db.note(&msg);
+            }
             db.emit();
+            false
+        } else {
+            true
         }
     }
 

compiler/rustc_lint/src/levels.rs

@@ -88,7 +88,7 @@ impl<'s> LintLevelsBuilder<'s> {
         self.sets.lint_cap = sess.opts.lint_cap.unwrap_or(Level::Forbid);
 
         for &(ref lint_name, level) in &sess.opts.lint_opts {
-            store.check_lint_name_cmdline(sess, &lint_name, level);
+            store.check_lint_name_cmdline(sess, &lint_name, Some(level));
             let orig_level = level;
 
             // If the cap is less than this specified level, e.g., if we've got
@@ -109,6 +109,16 @@ impl<'s> LintLevelsBuilder<'s> {
             }
         }
 
+        for lint_name in &sess.opts.force_warns {
+            let valid = store.check_lint_name_cmdline(sess, lint_name, None);
+            if valid {
+                let lints = store
+                    .find_lints(lint_name)
+                    .unwrap_or_else(|_| bug!("A valid lint failed to produce a lint ids"));
+                self.sets.force_warns.extend(&lints);
+            }
+        }
+
         self.sets.list.push(LintSet::CommandLine { specs });
     }
 
@@ -142,6 +152,9 @@ impl<'s> LintLevelsBuilder<'s> {
                     LintLevelSource::Default => false,
                     LintLevelSource::Node(symbol, _, _) => self.store.is_lint_group(symbol),
                     LintLevelSource::CommandLine(symbol, _) => self.store.is_lint_group(symbol),
+                    LintLevelSource::ForceWarn(_symbol) => {
+                        bug!("forced warn lint returned a forbid lint level")
+                    }
                 };
                 debug!(
                     "fcw_warning={:?}, specs.get(&id) = {:?}, old_src={:?}, id_name={:?}",
@@ -166,6 +179,7 @@ impl<'s> LintLevelsBuilder<'s> {
                         LintLevelSource::CommandLine(_, _) => {
                             diag_builder.note("`forbid` lint level was set on command line");
                         }
+                        _ => bug!("forced warn lint returned a forbid lint level"),
                     }
                     diag_builder.emit();
                 };

compiler/rustc_middle/src/lint.rs

@@ -1,7 +1,7 @@
 use std::cmp;
 
 use crate::ich::StableHashingContext;
-use rustc_data_structures::fx::FxHashMap;
+use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_errors::{DiagnosticBuilder, DiagnosticId};
 use rustc_hir::HirId;
@@ -28,6 +28,9 @@ pub enum LintLevelSource {
     /// The provided `Level` is the level specified on the command line.
     /// (The actual level may be lower due to `--cap-lints`.)
     CommandLine(Symbol, Level),
+
+    /// Lint is being forced to warn no matter what.
+    ForceWarn(Symbol),
 }
 
 impl LintLevelSource {
@@ -36,6 +39,7 @@ impl LintLevelSource {
             LintLevelSource::Default => symbol::kw::Default,
             LintLevelSource::Node(name, _, _) => name,
             LintLevelSource::CommandLine(name, _) => name,
+            LintLevelSource::ForceWarn(name) => name,
         }
     }
 
@@ -44,6 +48,7 @@ impl LintLevelSource {
             LintLevelSource::Default => DUMMY_SP,
             LintLevelSource::Node(_, span, _) => span,
             LintLevelSource::CommandLine(_, _) => DUMMY_SP,
+            LintLevelSource::ForceWarn(_) => DUMMY_SP,
         }
     }
 }
@@ -55,6 +60,7 @@ pub type LevelAndSource = (Level, LintLevelSource);
 pub struct LintLevelSets {
     pub list: Vec<LintSet>,
     pub lint_cap: Level,
+    pub force_warns: FxHashSet<LintId>,
 }
 
 #[derive(Debug)]
@@ -73,7 +79,11 @@ pub enum LintSet {
 
 impl LintLevelSets {
     pub fn new() -> Self {
-        LintLevelSets { list: Vec::new(), lint_cap: Level::Forbid }
+        LintLevelSets {
+            list: Vec::new(),
+            lint_cap: Level::Forbid,
+            force_warns: FxHashSet::default(),
+        }
     }
 
     pub fn get_lint_level(
@@ -83,6 +93,11 @@ impl LintLevelSets {
         aux: Option<&FxHashMap<LintId, LevelAndSource>>,
         sess: &Session,
     ) -> LevelAndSource {
+        // Check whether we should always warn
+        if self.force_warns.contains(&LintId::of(lint)) {
+            return (Level::Warn, LintLevelSource::ForceWarn(Symbol::intern(lint.name)));
+        }
+
         let (level, mut src) = self.get_lint_id_level(LintId::of(lint), idx, aux);
 
         // If `level` is none then we actually assume the default level for this
@@ -176,11 +191,11 @@ impl LintLevelMap {
 impl<'a> HashStable<StableHashingContext<'a>> for LintLevelMap {
     #[inline]
     fn hash_stable(&self, hcx: &mut StableHashingContext<'a>, hasher: &mut StableHasher) {
-        let LintLevelMap { ref sets, ref id_to_set } = *self;
+        let LintLevelMap { ref sets, ref id_to_set, .. } = *self;
 
         id_to_set.hash_stable(hcx, hasher);
 
-        let LintLevelSets { ref list, lint_cap } = *sets;
+        let LintLevelSets { ref list, lint_cap, .. } = *sets;
 
         lint_cap.hash_stable(hcx, hasher);
 
@@ -346,6 +361,13 @@ pub fn struct_lint_level<'s, 'd>(
                     );
                 }
             }
+            LintLevelSource::ForceWarn(_) => {
+                sess.diag_note_once(
+                    &mut err,
+                    DiagnosticMessageId::from(lint),
+                    "warning forced by `force-warns` commandline option",
+                );
+            }
         }
 
         err.code(DiagnosticId::Lint { name, has_future_breakage });

compiler/rustc_session/src/config.rs

@@ -677,6 +677,7 @@ impl Default for Options {
             optimize: OptLevel::No,
             debuginfo: DebugInfo::None,
             lint_opts: Vec::new(),
+            force_warns: Vec::new(),
             lint_cap: None,
             describe_lints: false,
             output_types: OutputTypes(BTreeMap::new()),
@@ -1092,6 +1093,13 @@ pub fn rustc_short_optgroups() -> Vec<RustcOptGroup> {
              level",
             "LEVEL",
         ),
+        opt::multi_s(
+            "",
+            "force-warns",
+            "Specifiy lints that should warn even if \
+             they are allowed somewhere else",
+            "LINT",
+        ),
         opt::multi_s("C", "codegen", "Set a codegen option", "OPT[=VALUE]"),
         opt::flag_s("V", "version", "Print version info and exit"),
         opt::flag_s("v", "verbose", "Use verbose output"),
@@ -1156,7 +1164,8 @@ pub fn rustc_optgroups() -> Vec<RustcOptGroup> {
 pub fn get_cmd_lint_options(
     matches: &getopts::Matches,
     error_format: ErrorOutputType,
-) -> (Vec<(String, lint::Level)>, bool, Option<lint::Level>) {
+    debugging_opts: &DebuggingOptions,
+) -> (Vec<(String, lint::Level)>, bool, Option<lint::Level>, Vec<String>) {
     let mut lint_opts_with_position = vec![];
     let mut describe_lints = false;
 
@@ -1189,7 +1198,18 @@ pub fn get_cmd_lint_options(
         lint::Level::from_str(&cap)
             .unwrap_or_else(|| early_error(error_format, &format!("unknown lint level: `{}`", cap)))
     });
-    (lint_opts, describe_lints, lint_cap)
+
+    if !debugging_opts.unstable_options && matches.opt_present("force-warns") {
+        early_error(
+            error_format,
+            "the `-Z unstable-options` flag must also be passed to enable \
+            the flag `--force-warns=lints`",
+        );
+    }
+
+    let force_warns = matches.opt_strs("force-warns");
+
+    (lint_opts, describe_lints, lint_cap, force_warns)
 }
 
 /// Parses the `--color` flag.
@@ -1926,9 +1946,10 @@ pub fn build_session_options(matches: &getopts::Matches) -> Options {
     let crate_types = parse_crate_types_from_list(unparsed_crate_types)
         .unwrap_or_else(|e| early_error(error_format, &e[..]));
 
-    let (lint_opts, describe_lints, lint_cap) = get_cmd_lint_options(matches, error_format);
-
     let mut debugging_opts = DebuggingOptions::build(matches, error_format);
+    let (lint_opts, describe_lints, lint_cap, force_warns) =
+        get_cmd_lint_options(matches, error_format, &debugging_opts);
+
     check_debug_option_stability(&debugging_opts, error_format, json_rendered);
 
     if !debugging_opts.unstable_options && json_unused_externs {
@@ -2100,6 +2121,7 @@ pub fn build_session_options(matches: &getopts::Matches) -> Options {
         optimize: opt_level,
         debuginfo,
         lint_opts,
+        force_warns,
         lint_cap,
         describe_lints,
         output_types,

compiler/rustc_session/src/options.rs

@@ -130,6 +130,7 @@ top_level_options!(
         debuginfo: DebugInfo [TRACKED],
         lint_opts: Vec<(String, lint::Level)> [TRACKED],
         lint_cap: Option<lint::Level> [TRACKED],
+        force_warns: Vec<String> [TRACKED],
         describe_lints: bool [UNTRACKED],
         output_types: OutputTypes [TRACKED],
         search_paths: Vec<SearchPath> [UNTRACKED],

src/doc/unstable-book/src/compiler-flags/force-warns.md

@@ -0,0 +1,21 @@
+# `force-warns`
+
+The tracking issue for this feature is: [#85512](https://github.com/rust-lang/rust/issues/85512).
+
+------------------------
+
+This feature allows you to cause any lint to produce a warning even if the lint has a different level by default or another level is set somewhere else. For instance, the `force-warns` option can be used to make a lint (e.g., `dead_code`) produce a warning even if that lint is allowed in code with `#![allow(dead_code)]`.
+
+## Example
+
+```rust,ignore (partial-example)
+#![allow(dead_code)]
+
+fn dead_function() {}
+// This would normally not produce a warning even though the
+// function is not used, because dead code is being allowed
+
+fn main() {}
+```
+
+We can force a warning to be produced by providing `--force-warns dead_code` to rustc.

src/librustdoc/config.rs

@@ -628,7 +628,8 @@ impl Options {
         let generate_redirect_map = matches.opt_present("generate-redirect-map");
         let show_type_layout = matches.opt_present("show-type-layout");
 
-        let (lint_opts, describe_lints, lint_cap) = get_cmd_lint_options(matches, error_format);
+        let (lint_opts, describe_lints, lint_cap, _) =
+            get_cmd_lint_options(matches, error_format, &debugging_opts);
 
         Ok(Options {
             input,

src/librustdoc/lib.rs

@@ -510,6 +510,14 @@ fn opts() -> Vec<RustcOptGroup> {
                 "LEVEL",
             )
         }),
+        unstable("force-warns", |o| {
+            o.optopt(
+                "",
+                "force-warns",
+                "Lints that will warn even if allowed somewhere else",
+                "LINTS",
+            )
+        }),
         unstable("index-page", |o| {
             o.optopt("", "index-page", "Markdown file to be used as index page", "PATH")
         }),

src/test/run-make/unstable-flag-required/Makefile

@@ -2,3 +2,4 @@
 
 all:
 	$(RUSTDOC) --output-format=json x.html 2>&1 | diff - output-format-json.stderr
+	$(RUSTC) --force-warns dead_code x.rs 2>&1 | diff - force-warns.stderr

src/test/run-make/unstable-flag-required/force-warns.stderr

@@ -0,0 +1,2 @@
+error: the `-Z unstable-options` flag must also be passed to enable the flag `--force-warns=lints`
+

src/test/ui/lint/force-warn/force-allowed-by-default-lint.rs

@@ -0,0 +1,11 @@
+// compile-flags: --force-warns elided_lifetimes_in_paths
+// check-pass
+
+struct Foo<'a> {
+    x: &'a u32,
+}
+
+fn foo(x: &Foo) {}
+//~^ WARN hidden lifetime parameters in types are deprecated
+
+fn main() {}

src/test/ui/lint/force-warn/force-allowed-by-default-lint.stderr

@@ -0,0 +1,10 @@
+warning: hidden lifetime parameters in types are deprecated
+  --> $DIR/force-allowed-by-default-lint.rs:8:12
+   |
+LL | fn foo(x: &Foo) {}
+   |            ^^^- help: indicate the anonymous lifetime: `<'_>`
+   |
+   = note: warning forced by `force-warns` commandline option
+
+warning: 1 warning emitted
+

src/test/ui/lint/force-warn/force-allowed-deny-by-default-lint.rs

@@ -0,0 +1,9 @@
+// compile-flags: --force-warns const_err
+// check-pass
+
+#![allow(const_err)]
+const C: i32 = 1 / 0;
+//~^ WARN any use of this value will cause an error
+//~| WARN this was previously accepted by the compiler
+
+fn main() {}

src/test/ui/lint/force-warn/force-allowed-deny-by-default-lint.stderr

@@ -0,0 +1,14 @@
+warning: any use of this value will cause an error
+  --> $DIR/force-allowed-deny-by-default-lint.rs:5:16
+   |
+LL | const C: i32 = 1 / 0;
+   | ---------------^^^^^-
+   |                |
+   |                attempt to divide `1_i32` by zero
+   |
+   = note: warning forced by `force-warns` commandline option
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #71800 <https://github.com/rust-lang/rust/issues/71800>
+
+warning: 1 warning emitted
+

src/test/ui/lint/force-warn/force-allowed-warning.rs

@@ -0,0 +1,9 @@
+// compile-flags: --force-warns dead_code
+// check-pass
+
+#![allow(dead_code)]
+
+fn dead_function() {}
+//~^ WARN function is never used
+
+fn main() {}

src/test/ui/lint/force-warn/force-allowed-warning.stderr

@@ -0,0 +1,10 @@
+warning: function is never used: `dead_function`
+  --> $DIR/force-allowed-warning.rs:6:4
+   |
+LL | fn dead_function() {}
+   |    ^^^^^^^^^^^^^
+   |
+   = note: warning forced by `force-warns` commandline option
+
+warning: 1 warning emitted
+