Make Emitter::emit_diagnostic consuming.

All the other `emit`/`emit_diagnostic` methods were recently made
consuming (e.g. rust-lang#119606), but this one wasn't. But it makes sense to.

Much of this is straightforward, and lots of `clone` calls are avoided.
There are a couple of tricky bits.
- `Emitter::primary_span_formatted` no longer takes a `Diagnostic` and
  returns a pair. Instead it takes the two fields from `Diagnostic` that
  it used (`span` and `suggestions`) as `&mut`, and modifies them. This
  is necessary to avoid the cloning of `diag.children` in two emitters.
- `from_errors_diagnostic` is rearranged so various uses of `diag` occur
  before the consuming `emit_diagnostic` call.

src/parse/session.rs

@@ -47,7 +47,7 @@ impl Emitter for SilentEmitter {
         None
     }
 
-    fn emit_diagnostic(&mut self, _db: &Diagnostic) {}
+    fn emit_diagnostic(&mut self, _db: Diagnostic) {}
 }
 
 fn silent_emitter() -> Box<DynEmitter> {
@@ -64,7 +64,7 @@ struct SilentOnIgnoredFilesEmitter {
 }
 
 impl SilentOnIgnoredFilesEmitter {
-    fn handle_non_ignoreable_error(&mut self, db: &Diagnostic) {
+    fn handle_non_ignoreable_error(&mut self, db: Diagnostic) {
         self.has_non_ignorable_parser_errors = true;
         self.can_reset.store(false, Ordering::Release);
         self.emitter.emit_diagnostic(db);
@@ -86,7 +86,7 @@ impl Emitter for SilentOnIgnoredFilesEmitter {
         None
     }
 
-    fn emit_diagnostic(&mut self, db: &Diagnostic) {
+    fn emit_diagnostic(&mut self, db: Diagnostic) {
         if db.level() == DiagnosticLevel::Fatal {
             return self.handle_non_ignoreable_error(db);
         }
@@ -365,7 +365,7 @@ mod tests {
                 None
             }
 
-            fn emit_diagnostic(&mut self, _db: &Diagnostic) {
+            fn emit_diagnostic(&mut self, _db: Diagnostic) {
                 self.num_emitted_errors.fetch_add(1, Ordering::Release);
             }
         }
@@ -424,7 +424,7 @@ mod tests {
             );
             let span = MultiSpan::from_span(mk_sp(BytePos(0), BytePos(1)));
             let fatal_diagnostic = build_diagnostic(DiagnosticLevel::Fatal, Some(span));
-            emitter.emit_diagnostic(&fatal_diagnostic);
+            emitter.emit_diagnostic(fatal_diagnostic);
             assert_eq!(num_emitted_errors.load(Ordering::Acquire), 1);
             assert_eq!(can_reset_errors.load(Ordering::Acquire), false);
         }
@@ -449,7 +449,7 @@ mod tests {
             );
             let span = MultiSpan::from_span(mk_sp(BytePos(0), BytePos(1)));
             let non_fatal_diagnostic = build_diagnostic(DiagnosticLevel::Warning, Some(span));
-            emitter.emit_diagnostic(&non_fatal_diagnostic);
+            emitter.emit_diagnostic(non_fatal_diagnostic);
             assert_eq!(num_emitted_errors.load(Ordering::Acquire), 0);
             assert_eq!(can_reset_errors.load(Ordering::Acquire), true);
         }
@@ -473,7 +473,7 @@ mod tests {
             );
             let span = MultiSpan::from_span(mk_sp(BytePos(0), BytePos(1)));
             let non_fatal_diagnostic = build_diagnostic(DiagnosticLevel::Warning, Some(span));
-            emitter.emit_diagnostic(&non_fatal_diagnostic);
+            emitter.emit_diagnostic(non_fatal_diagnostic);
             assert_eq!(num_emitted_errors.load(Ordering::Acquire), 1);
             assert_eq!(can_reset_errors.load(Ordering::Acquire), false);
         }
@@ -512,9 +512,9 @@ mod tests {
             let bar_diagnostic = build_diagnostic(DiagnosticLevel::Warning, Some(bar_span));
             let foo_diagnostic = build_diagnostic(DiagnosticLevel::Warning, Some(foo_span));
             let fatal_diagnostic = build_diagnostic(DiagnosticLevel::Fatal, None);
-            emitter.emit_diagnostic(&bar_diagnostic);
-            emitter.emit_diagnostic(&foo_diagnostic);
-            emitter.emit_diagnostic(&fatal_diagnostic);
+            emitter.emit_diagnostic(bar_diagnostic);
+            emitter.emit_diagnostic(foo_diagnostic);
+            emitter.emit_diagnostic(fatal_diagnostic);
             assert_eq!(num_emitted_errors.load(Ordering::Acquire), 2);
             assert_eq!(can_reset_errors.load(Ordering::Acquire), false);
         }