rustc_lint: Prevent multiple 'lint ignored' lints

Prevent multiple 'ignored unless specified at crate level' lints. The
multiplication happens because we run the same lint three times:
* In BuiltinCombinedEarlyLintPass
* In BuiltinCombinedPreExpansionLintPass
* In shallow_lint_levels_on

Only run the lint one time by checking the `lint_added_lints` bool.

Author: Enselic

compiler/rustc_lint/src/levels.rs

@@ -1029,7 +1029,7 @@ impl<'s, P: LintLevelsProvider> LintLevelsBuilder<'s, P> {
             }
         }
 
-        if !is_crate_node {
+        if self.lint_added_lints && !is_crate_node {
             for (id, &(level, ref src)) in self.current_specs().iter() {
                 if !id.lint.crate_level_only {
                     continue;

tests/ui/lint/crate_level_only_lint.rs

@@ -3,20 +3,14 @@
 mod foo {
 #![allow(uncommon_codepoints)]
 //~^ ERROR allow(uncommon_codepoints) is ignored unless specified at crate level [unused_attributes]
-//~| ERROR allow(uncommon_codepoints) is ignored unless specified at crate level [unused_attributes]
-//~| ERROR allow(uncommon_codepoints) is ignored unless specified at crate level [unused_attributes]
 
 #[allow(uncommon_codepoints)]
 //~^ ERROR allow(uncommon_codepoints) is ignored unless specified at crate level [unused_attributes]
-//~| ERROR allow(uncommon_codepoints) is ignored unless specified at crate level [unused_attributes]
-//~| ERROR allow(uncommon_codepoints) is ignored unless specified at crate level [unused_attributes]
 const BAR: f64 = 0.000001;
 
 }
 
 #[allow(uncommon_codepoints)]
 //~^ ERROR allow(uncommon_codepoints) is ignored unless specified at crate level [unused_attributes]
-//~| ERROR allow(uncommon_codepoints) is ignored unless specified at crate level [unused_attributes]
-//~| ERROR allow(uncommon_codepoints) is ignored unless specified at crate level [unused_attributes]
 fn main() {
 }

tests/ui/lint/crate_level_only_lint.stderr

@@ -11,64 +11,16 @@ LL | #![deny(uncommon_codepoints, unused_attributes)]
    |                              ^^^^^^^^^^^^^^^^^
 
 error: allow(uncommon_codepoints) is ignored unless specified at crate level
-  --> $DIR/crate_level_only_lint.rs:9:9
+  --> $DIR/crate_level_only_lint.rs:7:9
    |
 LL | #[allow(uncommon_codepoints)]
    |         ^^^^^^^^^^^^^^^^^^^
 
 error: allow(uncommon_codepoints) is ignored unless specified at crate level
-  --> $DIR/crate_level_only_lint.rs:17:9
+  --> $DIR/crate_level_only_lint.rs:13:9
    |
 LL | #[allow(uncommon_codepoints)]
    |         ^^^^^^^^^^^^^^^^^^^
 
-error: allow(uncommon_codepoints) is ignored unless specified at crate level
-  --> $DIR/crate_level_only_lint.rs:4:10
-   |
-LL | #![allow(uncommon_codepoints)]
-   |          ^^^^^^^^^^^^^^^^^^^
-   |
-   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
-
-error: allow(uncommon_codepoints) is ignored unless specified at crate level
-  --> $DIR/crate_level_only_lint.rs:9:9
-   |
-LL | #[allow(uncommon_codepoints)]
-   |         ^^^^^^^^^^^^^^^^^^^
-   |
-   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
-
-error: allow(uncommon_codepoints) is ignored unless specified at crate level
-  --> $DIR/crate_level_only_lint.rs:17:9
-   |
-LL | #[allow(uncommon_codepoints)]
-   |         ^^^^^^^^^^^^^^^^^^^
-   |
-   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
-
-error: allow(uncommon_codepoints) is ignored unless specified at crate level
-  --> $DIR/crate_level_only_lint.rs:4:10
-   |
-LL | #![allow(uncommon_codepoints)]
-   |          ^^^^^^^^^^^^^^^^^^^
-   |
-   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
-
-error: allow(uncommon_codepoints) is ignored unless specified at crate level
-  --> $DIR/crate_level_only_lint.rs:9:9
-   |
-LL | #[allow(uncommon_codepoints)]
-   |         ^^^^^^^^^^^^^^^^^^^
-   |
-   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
-
-error: allow(uncommon_codepoints) is ignored unless specified at crate level
-  --> $DIR/crate_level_only_lint.rs:17:9
-   |
-LL | #[allow(uncommon_codepoints)]
-   |         ^^^^^^^^^^^^^^^^^^^
-   |
-   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
-
-error: aborting due to 9 previous errors
+error: aborting due to 3 previous errors