Don't hash lints differently to non-lints.

compiler/rustc_errors/src/diagnostic.rs

@@ -109,8 +109,6 @@ pub struct Diagnostic {
     /// `span` if there is one. Otherwise, it is `DUMMY_SP`.
     pub sort_span: Span,
 
-    /// If diagnostic is from Lint, custom hash function ignores children.
-    /// Otherwise hash is based on the all the fields.
     pub is_lint: Option<IsLint>,
 
     /// With `-Ztrack_diagnostics` enabled,
@@ -980,22 +978,24 @@ impl Diagnostic {
     ) -> (
         &Level,
         &[(DiagnosticMessage, Style)],
-        Vec<(&Cow<'static, str>, &DiagnosticArgValue)>,
         &Option<ErrCode>,
-        &Option<IsLint>,
         &MultiSpan,
+        &[SubDiagnostic],
         &Result<Vec<CodeSuggestion>, SuggestionsDisabled>,
-        Option<&[SubDiagnostic]>,
+        Vec<(&DiagnosticArgName, &DiagnosticArgValue)>,
+        &Option<IsLint>,
     ) {
         (
             &self.level,
             &self.messages,
-            self.args().collect(),
             &self.code,
-            &self.is_lint,
             &self.span,
+            &self.children,
             &self.suggestions,
-            (if self.is_lint.is_some() { None } else { Some(&self.children) }),
+            self.args().collect(),
+            // omit self.sort_span
+            &self.is_lint,
+            // omit self.emitted_at
         )
     }
 }

src/tools/clippy/tests/ui/same_name_method.rs

@@ -74,6 +74,7 @@ mod should_lint {
         impl S {
             fn foo() {}
             //~^ ERROR: method's name is the same as an existing method in a trait
+            //~| ERROR: method's name is the same as an existing method in a trait
         }
 
         impl T1 for S {}

src/tools/clippy/tests/ui/same_name_method.stderr

@@ -56,10 +56,22 @@ LL |             fn foo() {}
    |             ^^^^^^^^^^^
    |
 note: existing `foo` defined here
-  --> $DIR/same_name_method.rs:79:9
+  --> $DIR/same_name_method.rs:80:9
    |
 LL |         impl T1 for S {}
    |         ^^^^^^^^^^^^^^^^
 
-error: aborting due to 5 previous errors
+error: method's name is the same as an existing method in a trait
+  --> $DIR/same_name_method.rs:75:13
+   |
+LL |             fn foo() {}
+   |             ^^^^^^^^^^^
+   |
+note: existing `foo` defined here
+  --> $DIR/same_name_method.rs:82:9
+   |
+LL |         impl T2 for S {}
+   |         ^^^^^^^^^^^^^^^^
+
+error: aborting due to 6 previous errors
 

tests/rustdoc-ui/unescaped_backticks.stderr

@@ -302,7 +302,6 @@ LL | |     /// level changes.
    = help: if you meant to use a literal backtick, escape it
             change: or `None` if it isn't.
            to this: or `None\` if it isn't.
-   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: unescaped backtick
   --> $DIR/unescaped_backticks.rs:323:5
@@ -322,7 +321,6 @@ LL | |     /// level changes.
    = help: if you meant to use a literal backtick, escape it
             change: `on_event` should be called.
            to this: `on_event\` should be called.
-   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: unescaped backtick
   --> $DIR/unescaped_backticks.rs:323:5
@@ -342,7 +340,6 @@ LL | |     /// level changes.
    = help: if you meant to use a literal backtick, escape it
             change: [`rebuild_interest_cache`][rebuild] is called after the value of the max
            to this: [`rebuild_interest_cache\`][rebuild] is called after the value of the max
-   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: unescaped backtick
   --> $DIR/unescaped_backticks.rs:349:56

tests/ui/consts/const-eval/stable-metric/ctfe-simple-loop.warn.stderr

@@ -40,7 +40,6 @@ help: the constant being evaluated
    |
 LL | const Y: u32 = simple_loop(35);
    | ^^^^^^^^^^^^
-   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: constant evaluation is taking a long time
   --> $DIR/ctfe-simple-loop.rs:9:5

tests/ui/imports/ambiguous-9.stderr

@@ -60,7 +60,6 @@ note: `date_range` could also refer to the function imported here
 LL | use prelude::*;
    |     ^^^^^^^^^^
    = help: consider adding an explicit import of `date_range` to disambiguate
-   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: 4 warnings emitted