Auto merge of #87472 - inquisitivecrystal:stabilize-force-warn, r=Mark-Simulacrum

Stabilize and document `--force-warn`

This PR will stabilize and document the `--force-warn` command line option. It is currently a draft, pending an FCP.

I've taken the liberty of tidying up the lint level command line options a bit as part of this. The changes are quite minor and should only affect rustc's help output. I'm making them here because they're trivial and, in one case, necessary to unify the way `--force-warn` with the way the other options are displayed.

I also want to mention that `@rylev` has done a ton of work on moving this along and deserves most of the credit. I'm just the one who landed up writing this particular PR.

Resolves #86516.

Author: bors

compiler/rustc_session/src/config.rs

@@ -1089,10 +1089,11 @@ pub fn rustc_short_optgroups() -> Vec<RustcOptGroup> {
         ),
         opt::flag_s("", "test", "Build a test harness"),
         opt::opt_s("", "target", "Target triple for which the code is compiled", "TARGET"),
-        opt::multi_s("W", "warn", "Set lint warnings", "OPT"),
-        opt::multi_s("A", "allow", "Set lint allowed", "OPT"),
-        opt::multi_s("D", "deny", "Set lint denied", "OPT"),
-        opt::multi_s("F", "forbid", "Set lint forbidden", "OPT"),
+        opt::multi_s("A", "allow", "Set lint allowed", "LINT"),
+        opt::multi_s("W", "warn", "Set lint warnings", "LINT"),
+        opt::multi_s("", "force-warn", "Set lint force-warn", "LINT"),
+        opt::multi_s("D", "deny", "Set lint denied", "LINT"),
+        opt::multi_s("F", "forbid", "Set lint forbidden", "LINT"),
         opt::multi_s(
             "",
             "cap-lints",
@@ -1101,13 +1102,6 @@ pub fn rustc_short_optgroups() -> Vec<RustcOptGroup> {
              level",
             "LEVEL",
         ),
-        opt::multi_s(
-            "",
-            "force-warn",
-            "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"),
@@ -1163,19 +1157,10 @@ pub fn rustc_optgroups() -> Vec<RustcOptGroup> {
 pub fn get_cmd_lint_options(
     matches: &getopts::Matches,
     error_format: ErrorOutputType,
-    debugging_opts: &DebuggingOptions,
 ) -> (Vec<(String, lint::Level)>, bool, Option<lint::Level>) {
     let mut lint_opts_with_position = vec![];
     let mut describe_lints = false;
 
-    if !debugging_opts.unstable_options && matches.opt_present("force-warn") {
-        early_error(
-            error_format,
-            "the `-Z unstable-options` flag must also be passed to enable \
-            the flag `--force-warn=lints`",
-        );
-    }
-
     for level in [lint::Allow, lint::Warn, lint::ForceWarn, lint::Deny, lint::Forbid] {
         for (arg_pos, lint_name) in matches.opt_strs_pos(level.as_str()) {
             if lint_name == "help" {
@@ -1965,8 +1950,7 @@ pub fn build_session_options(matches: &getopts::Matches) -> Options {
         .unwrap_or_else(|e| early_error(error_format, &e[..]));
 
     let mut debugging_opts = DebuggingOptions::build(matches, error_format);
-    let (lint_opts, describe_lints, lint_cap) =
-        get_cmd_lint_options(matches, error_format, &debugging_opts);
+    let (lint_opts, describe_lints, lint_cap) = get_cmd_lint_options(matches, error_format);
 
     check_debug_option_stability(&debugging_opts, error_format, json_rendered);
 

src/doc/rustc/src/lints/levels.md

@@ -1,11 +1,12 @@
 # Lint levels
 
-In `rustc`, lints are divided into four *levels*:
+In `rustc`, lints are divided into five *levels*:
 
 1. allow
 2. warn
-3. deny
-4. forbid
+3. force-warn
+4. deny
+5. forbid
 
 Each lint has a default level (explained in the lint listing later in this
 chapter), and the compiler has a default warning level. First, let's explain
@@ -57,6 +58,14 @@ warning: unused variable: `x`
   = note: to avoid this warning, consider using `_x` instead
 ```
 
+## force-warn
+
+'force-warn' is a special lint level. It's the same as 'warn' in that a lint
+at this level will produce a warning, but unlike the 'warn' level, the
+'force-warn' level cannot be overridden. If a lint is set to 'force-warn', it
+is guaranteed to warn: no more, no less. This is true even if the overall lint
+level is capped via cap-lints.
+
 ## deny
 
 A 'deny' lint produces an error if you violate it. For example, this code
@@ -87,11 +96,12 @@ This lint level gives you that.
 
 ## forbid
 
-'forbid' is a special lint level that's stronger than 'deny'. It's the same
-as 'deny' in that a lint at this level will produce an error, but unlike the
-'deny' level, the 'forbid' level can not be overridden to be anything lower
-than an error.  However, lint levels may still be capped with `--cap-lints`
-(see below) so `rustc --cap-lints warn` will make lints set to 'forbid' just
+'forbid' is a special lint level that fills the same role for 'deny' that
+'force-warn' does for 'warn'. It's the same as 'deny' in that a lint at this
+level will produce an error, but unlike the 'deny' level, the 'forbid' level
+can not be overridden to be anything lower than an error.  However, lint
+levels may still be capped with `--cap-lints` (see below) so `rustc --cap-
+lints warn` will make lints set to 'forbid' just
 warn.
 
 ## Configuring warning levels
@@ -113,8 +123,8 @@ certain lint levels. We'll talk about that last.
 
 ### Via compiler flag
 
-The `-A`, `-W`, `-D`, and `-F` flags let you turn one or more lints
-into allowed, warning, deny, or forbid levels, like this:
+The `-A`, `-W`, `--force-warn` `-D`, and `-F` flags let you turn one or more lints
+into allowed, warning, force-warn, deny, or forbid levels, like this:
 
 ```bash
 $ rustc lib.rs --crate-type=lib -W missing-docs
@@ -158,7 +168,7 @@ You can also pass each flag more than once for changing multiple lints:
 $ rustc lib.rs --crate-type=lib -D missing-docs -D unused-variables
 ```
 
-And of course, you can mix these four flags together:
+And of course, you can mix these five flags together:
 
 ```bash
 $ rustc lib.rs --crate-type=lib -D missing-docs -A unused-variables
@@ -176,6 +186,10 @@ You can make use of this behavior by overriding the level of one specific lint o
 $ rustc lib.rs --crate-type=lib -D unused -A unused-variables
 ```
 
+Since `force-warn` and `forbid` cannot be overridden, setting
+one of them will prevent any later level for the same lint from
+taking effect.
+
 ### Via an attribute
 
 You can also modify the lint level with a crate-wide attribute:
@@ -207,7 +221,8 @@ warning: missing documentation for a function
   | ^^^^^^^^^^^^
 ```
 
-All four, `warn`, `allow`, `deny`, and `forbid` all work this way.
+`warn`, `allow`, `deny`, and `forbid` all work this way. There is
+no way to set a lint to `force-warn` using an attribute.
 
 You can also pass in multiple lints per attribute:
 

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

@@ -671,8 +671,7 @@ impl Options {
             return Err(1);
         }
 
-        let (lint_opts, describe_lints, lint_cap) =
-            get_cmd_lint_options(matches, error_format, &debugging_opts);
+        let (lint_opts, describe_lints, lint_cap) = get_cmd_lint_options(matches, error_format);
 
         Ok(Options {
             input,

src/librustdoc/config.rs

@@ -503,10 +503,11 @@ fn opts() -> Vec<RustcOptGroup> {
         unstable("disable-minification", |o| {
             o.optflagmulti("", "disable-minification", "Disable minification applied on JS files")
         }),
-        stable("warn", |o| o.optmulti("W", "warn", "Set lint warnings", "OPT")),
-        stable("allow", |o| o.optmulti("A", "allow", "Set lint allowed", "OPT")),
-        stable("deny", |o| o.optmulti("D", "deny", "Set lint denied", "OPT")),
-        stable("forbid", |o| o.optmulti("F", "forbid", "Set lint forbidden", "OPT")),
+        stable("allow", |o| o.optmulti("A", "allow", "Set lint allowed", "LINT")),
+        stable("warn", |o| o.optmulti("W", "warn", "Set lint warnings", "LINT")),
+        stable("force-warn", |o| o.optmulti("", "force-warn", "Set lint force-warn", "LINT")),
+        stable("deny", |o| o.optmulti("D", "deny", "Set lint denied", "LINT")),
+        stable("forbid", |o| o.optmulti("F", "forbid", "Set lint forbidden", "LINT")),
         stable("cap-lints", |o| {
             o.optmulti(
                 "",
@@ -517,14 +518,6 @@ fn opts() -> Vec<RustcOptGroup> {
                 "LEVEL",
             )
         }),
-        unstable("force-warn", |o| {
-            o.optopt(
-                "",
-                "force-warn",
-                "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/librustdoc/lib.rs

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

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

@@ -5,7 +5,7 @@
 //
 //[warn_deny] compile-flags: --warn missing_abi --deny missing_abi
 //[forbid_warn] compile-flags: --warn missing_abi --forbid missing_abi
-//[force_warn_deny] compile-flags: -Z unstable-options --force-warn missing_abi --allow missing_abi
+//[force_warn_deny] compile-flags: --force-warn missing_abi --allow missing_abi
 //[force_warn_deny] check-pass
 
 

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

@@ -1,7 +1,7 @@
 // Checks that rustc correctly errors when passed an invalid lint with
 // `--force-warn`. This is a regression test for issue #86958.
 //
-// compile-flags: -Z unstable-options --force-warn foo-qux
+// compile-flags: --force-warn foo-qux
 // error-pattern: unknown lint: `foo_qux`
 
 fn main() {}

src/test/ui/lint/cli-lint-override.rs

@@ -6,10 +6,6 @@ error[E0602]: unknown lint: `foo_qux`
    |
    = note: requested on the command line with `--force-warn foo_qux`
 
-error[E0602]: unknown lint: `foo_qux`
-   |
-   = note: requested on the command line with `--force-warn foo_qux`
-
-error: aborting due to 3 previous errors
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0602`.