rustc_session: allow overriding lint level of individual lints from a group

src/doc/rustc/src/command-line-arguments.md

@@ -215,21 +215,29 @@ This controls which [target](targets/index.md) to produce.
 
 This flag will set which lints should be set to the [warn level](lints/levels.md#warn).
 
+_Note:_ The order of these lint level arguments is taken into account, see [lint level via compiler flag](lints/levels.md#via-compiler-flag) for more information.
+
 <a id="option-a-allow"></a>
 ## `-A`: set lint allowed
 
 This flag will set which lints should be set to the [allow level](lints/levels.md#allow).
 
+_Note:_ The order of these lint level arguments is taken into account, see [lint level via compiler flag](lints/levels.md#via-compiler-flag) for more information.
+
 <a id="option-d-deny"></a>
 ## `-D`: set lint denied
 
 This flag will set which lints should be set to the [deny level](lints/levels.md#deny).
 
+_Note:_ The order of these lint level arguments is taken into account, see [lint level via compiler flag](lints/levels.md#via-compiler-flag) for more information.
+
 <a id="option-f-forbid"></a>
 ## `-F`: set lint forbidden
 
 This flag will set which lints should be set to the [forbid level](lints/levels.md#forbid).
 
+_Note:_ The order of these lint level arguments is taken into account, see [lint level via compiler flag](lints/levels.md#via-compiler-flag) for more information.
+
 <a id="option-z-unstable"></a>
 ## `-Z`: set unstable options
 

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

@@ -164,6 +164,18 @@ And of course, you can mix these four flags together:
 $ rustc lib.rs --crate-type=lib -D missing-docs -A unused-variables
 ```
 
+The order of these command line arguments is taken into account. The following allows the `unused-variables` lint, because it is the last argument for that lint:
+
+```bash
+$ rustc lib.rs --crate-type=lib -D unused-variables -A unused-variables
+```
+
+You can make use of this behavior by overriding the level of one specific lint out of a group of lints. The following example denies all the lints in the `unused` group, but explicitly allows the `unused-variables` lint in that group:
+
+```bash
+$ rustc lib.rs --crate-type=lib -D unused -A unused-variables
+```
+
 ### Via an attribute
 
 You can also modify the lint level with a crate-wide attribute:

src/librustc_session/config.rs

@@ -986,19 +986,26 @@ pub fn get_cmd_lint_options(
     matches: &getopts::Matches,
     error_format: ErrorOutputType,
 ) -> (Vec<(String, lint::Level)>, bool, Option<lint::Level>) {
-    let mut lint_opts = vec![];
+    let mut lint_opts_with_position = vec![];
     let mut describe_lints = false;
 
     for &level in &[lint::Allow, lint::Warn, lint::Deny, lint::Forbid] {
-        for lint_name in matches.opt_strs(level.as_str()) {
+        for (arg_pos, lint_name) in matches.opt_strs_pos(level.as_str()) {
             if lint_name == "help" {
                 describe_lints = true;
             } else {
-                lint_opts.push((lint_name.replace("-", "_"), level));
+                lint_opts_with_position.push((arg_pos, lint_name.replace("-", "_"), level));
             }
         }
     }
 
+    lint_opts_with_position.sort_by_key(|x| x.0);
+    let lint_opts = lint_opts_with_position
+        .iter()
+        .cloned()
+        .map(|(_, lint_name, level)| (lint_name, level))
+        .collect();
+
     let lint_cap = matches.opt_str("cap-lints").map(|cap| {
         lint::Level::from_str(&cap)
             .unwrap_or_else(|| early_error(error_format, &format!("unknown lint level: `{}`", cap)))

src/test/ui-fulldeps/lint-group-denied-lint-allowed.rs

@@ -0,0 +1,7 @@
+// aux-build:lint-group-plugin-test.rs
+// check-pass
+// compile-flags: -D unused -A unused-variables
+
+fn main() {
+    let x = 1;
+}

src/tools/compiletest/src/runtest.rs

@@ -1478,11 +1478,7 @@ impl<'test> TestCx<'test> {
             WillExecute::No => TargetLocation::ThisDirectory(self.output_base_dir()),
         };
 
-        let mut rustc = self.make_compile_args(&self.testpaths.file, output_file, emit_metadata);
-
-        rustc.arg("-L").arg(&self.aux_output_dir_name());
-
-        match self.config.mode {
+        let allow_unused = match self.config.mode {
             CompileFail | Ui => {
                 // compile-fail and ui tests tend to have tons of unused code as
                 // it's just testing various pieces of the compile, but we don't
@@ -1495,11 +1491,18 @@ impl<'test> TestCx<'test> {
                     // via command line flags.
                     && local_pm != Some(PassMode::Run)
                 {
-                    rustc.args(&["-A", "unused"]);
+                    AllowUnused::Yes
+                } else {
+                    AllowUnused::No
                 }
             }
-            _ => {}
-        }
+            _ => AllowUnused::No,
+        };
+
+        let mut rustc =
+            self.make_compile_args(&self.testpaths.file, output_file, emit_metadata, allow_unused);
+
+        rustc.arg("-L").arg(&self.aux_output_dir_name());
 
         self.compose_and_run_compiler(rustc, None)
     }
@@ -1710,7 +1713,8 @@ impl<'test> TestCx<'test> {
         // Create the directory for the stdout/stderr files.
         create_dir_all(aux_cx.output_base_dir()).unwrap();
         let input_file = &aux_testpaths.file;
-        let mut aux_rustc = aux_cx.make_compile_args(input_file, aux_output, EmitMetadata::No);
+        let mut aux_rustc =
+            aux_cx.make_compile_args(input_file, aux_output, EmitMetadata::No, AllowUnused::No);
 
         let (dylib, crate_type) = if aux_props.no_prefer_dynamic {
             (true, None)
@@ -1819,6 +1823,7 @@ impl<'test> TestCx<'test> {
         input_file: &Path,
         output_file: TargetLocation,
         emit_metadata: EmitMetadata,
+        allow_unused: AllowUnused,
     ) -> Command {
         let is_rustdoc = self.is_rustdoc();
         let mut rustc = if !is_rustdoc {
@@ -1951,6 +1956,10 @@ impl<'test> TestCx<'test> {
             rustc.arg("-Ctarget-feature=-crt-static");
         }
 
+        if let AllowUnused::Yes = allow_unused {
+            rustc.args(&["-A", "unused"]);
+        }
+
         rustc.args(&self.props.compile_flags);
 
         rustc
@@ -2134,7 +2143,8 @@ impl<'test> TestCx<'test> {
 
         let output_file = TargetLocation::ThisDirectory(self.output_base_dir());
         let input_file = &self.testpaths.file;
-        let mut rustc = self.make_compile_args(input_file, output_file, EmitMetadata::No);
+        let mut rustc =
+            self.make_compile_args(input_file, output_file, EmitMetadata::No, AllowUnused::No);
         rustc.arg("-L").arg(aux_dir).arg("--emit=llvm-ir");
 
         self.compose_and_run_compiler(rustc, None)
@@ -2147,7 +2157,8 @@ impl<'test> TestCx<'test> {
 
         let output_file = TargetLocation::ThisFile(output_path.clone());
         let input_file = &self.testpaths.file;
-        let mut rustc = self.make_compile_args(input_file, output_file, EmitMetadata::No);
+        let mut rustc =
+            self.make_compile_args(input_file, output_file, EmitMetadata::No, AllowUnused::No);
 
         rustc.arg("-L").arg(self.aux_output_dir_name());
 
@@ -2999,6 +3010,7 @@ impl<'test> TestCx<'test> {
                 &self.testpaths.file.with_extension(UI_FIXED),
                 TargetLocation::ThisFile(self.make_exe_name()),
                 emit_metadata,
+                AllowUnused::No,
             );
             rustc.arg("-L").arg(&self.aux_output_dir_name());
             let res = self.compose_and_run_compiler(rustc, None);
@@ -3486,6 +3498,11 @@ enum ExpectedLine<T: AsRef<str>> {
     Text(T),
 }
 
+enum AllowUnused {
+    Yes,
+    No,
+}
+
 impl<T> fmt::Debug for ExpectedLine<T>
 where
     T: AsRef<str> + fmt::Debug,