note lint group set on command line triggering individual lint

Previously, the note/message for the source of a lint being the command
line unconditionally named the individual lint, even if the actual
command specified a lint group (e.g., `-D warnings`); here, we take note
of the actual command options so we can be more specific.

This remains in the matter of #36846.

src/librustc/lint/context.rs

@@ -43,6 +43,7 @@ use std::fmt;
 use std::ops::Deref;
 use syntax::attr;
 use syntax::ast;
+use syntax::symbol::Symbol;
 use syntax_pos::{MultiSpan, Span};
 use errors::{self, Diagnostic, DiagnosticBuilder};
 use hir;
@@ -300,8 +301,9 @@ impl LintStore {
             check_lint_name_cmdline(sess, self,
                                     &lint_name[..], level);
 
+            let lint_flag_val = Symbol::intern(&lint_name);
             match self.find_lint(&lint_name[..], sess, None) {
-                Ok(lint_id) => self.set_level(lint_id, (level, CommandLine)),
+                Ok(lint_id) => self.set_level(lint_id, (level, CommandLine(lint_flag_val))),
                 Err(FindLintError::Removed) => { }
                 Err(_) => {
                     match self.lint_groups.iter().map(|(&x, pair)| (x, pair.0.clone()))
@@ -311,7 +313,7 @@ impl LintStore {
                         Some(v) => {
                             v.iter()
                              .map(|lint_id: &LintId|
-                                     self.set_level(*lint_id, (level, CommandLine)))
+                                     self.set_level(*lint_id, (level, CommandLine(lint_flag_val))))
                              .collect::<Vec<()>>();
                         }
                         None => {
@@ -470,12 +472,20 @@ pub fn raw_struct_lint<'a, S>(sess: &'a Session,
         Default => {
             err.note(&format!("#[{}({})] on by default", level.as_str(), name));
         },
-        CommandLine => {
-            err.note(&format!("[-{} {}]",
-                              match level {
-                                  Warn => 'W', Deny => 'D', Forbid => 'F',
-                                  Allow => bug!()
-                              }, name.replace("_", "-")));
+        CommandLine(lint_flag_val) => {
+            let flag = match level {
+                Warn => "-W", Deny => "-D", Forbid => "-F",
+                Allow => bug!("earlier conditional return should handle Allow case")
+            };
+            let hyphen_case_lint_name = name.replace("_", "-");
+            if lint_flag_val.as_str().deref() == name {
+                err.note(&format!("requested on the command line with `{} {}`",
+                                  flag, hyphen_case_lint_name));
+            } else {
+                let hyphen_case_flag_val = lint_flag_val.as_str().replace("_", "-");
+                err.note(&format!("`{} {}` implies `{} {}`",
+                                  flag, hyphen_case_flag_val, flag, hyphen_case_lint_name));
+            }
         },
         Node(lint_attr_name, src) => {
             def = Some(src);
@@ -671,7 +681,7 @@ pub trait LintContext<'tcx>: Sized {
                             diag_builder.span_label(forbid_source_span,
                                                     &format!("`forbid` level set here"))
                         },
-                        LintSource::CommandLine => {
+                        LintSource::CommandLine(_) => {
                             diag_builder.note("`forbid` lint level was set on command line")
                         }
                     }.emit()

src/librustc/lint/mod.rs

@@ -38,6 +38,7 @@ use std::ascii::AsciiExt;
 use syntax_pos::Span;
 use syntax::visit as ast_visit;
 use syntax::ast;
+use syntax::symbol::Symbol;
 
 pub use lint::context::{LateContext, EarlyContext, LintContext, LintStore,
                         raw_emit_lint, check_crate, check_ast_crate, gather_attrs,
@@ -341,7 +342,7 @@ pub enum LintSource {
     Node(ast::Name, Span),
 
     /// Lint level was set by a command-line flag.
-    CommandLine,
+    CommandLine(Symbol),
 }
 
 pub type LevelSource = (Level, LintSource);

src/test/compile-fail/lint-output-format-2.rs

@@ -13,7 +13,7 @@
 
 #![feature(foo)]
 //~^ ERROR unused or unknown feature
-//~| NOTE [-F unused-features]
+//~| NOTE requested on the command line with `-F unused-features`
 
 #![feature(test_feature)]
 

src/test/ui/lint/command-line-lint-group-allow.rs

@@ -0,0 +1,15 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// compile-flags: -A bad-style
+
+fn main() {
+    let _InappropriateCamelCasing = true;
+}

src/test/ui/lint/command-line-lint-group-deny.rs

@@ -0,0 +1,15 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// compile-flags: -D bad-style
+
+fn main() {
+    let _InappropriateCamelCasing = true;
+}

src/test/ui/lint/command-line-lint-group-deny.stderr

@@ -0,0 +1,10 @@
+error: variable `_InappropriateCamelCasing` should have a snake case name such as `_inappropriate_camel_casing`
+  --> $DIR/command-line-lint-group-deny.rs:14:9
+   |
+14 |     let _InappropriateCamelCasing = true;
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: `-D bad-style` implies `-D non-snake-case`
+
+error: aborting due to previous error
+

src/test/ui/lint/command-line-lint-group-forbid.rs

@@ -0,0 +1,15 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// compile-flags: -F bad-style
+
+fn main() {
+    let _InappropriateCamelCasing = true;
+}

src/test/ui/lint/command-line-lint-group-forbid.stderr

@@ -0,0 +1,10 @@
+error: variable `_InappropriateCamelCasing` should have a snake case name such as `_inappropriate_camel_casing`
+  --> $DIR/command-line-lint-group-forbid.rs:14:9
+   |
+14 |     let _InappropriateCamelCasing = true;
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: `-F bad-style` implies `-F non-snake-case`
+
+error: aborting due to previous error
+

src/test/ui/lint/command-line-lint-group-warn.rs

@@ -0,0 +1,15 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// compile-flags: -W bad-style
+
+fn main() {
+    let _InappropriateCamelCasing = true;
+}

src/test/ui/lint/command-line-lint-group-warn.stderr

@@ -0,0 +1,8 @@
+warning: variable `_InappropriateCamelCasing` should have a snake case name such as `_inappropriate_camel_casing`
+  --> $DIR/command-line-lint-group-warn.rs:14:9
+   |
+14 |     let _InappropriateCamelCasing = true;
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: `-W bad-style` implies `-W non-snake-case`
+