[CodeCompletion] Skip conjuction elements that are unrelated to the code completion token

Author: ahoppen

lib/Sema/CSSyntacticElement.cpp

@@ -1030,6 +1030,19 @@ class SyntacticElementConstraintGenerator
 
     SmallVector<ElementInfo, 4> elements;
     for (auto element : braceStmt->getElements()) {
+      if (cs.isForCodeCompletion() && !cs.containsIDEInspectionTarget(element)) {
+        // Statements and expressions can't influence the expresion that
+        // contains the code completion token. To improve performance, skip
+        // type checking them entirely.
+        if (element.is<Expr *>()) {
+          continue;
+        } else if (element.is<Stmt *>() && !element.isStmt(StmtKind::Guard)) {
+          // Guard statements might define variables that are used in the code
+          // completion expression. Don't skip them.
+          continue;
+        }
+      }
+      
       if (auto *decl = element.dyn_cast<Decl *>()) {
         if (auto *PDB = dyn_cast<PatternBindingDecl>(decl)) {
           visitPatternBinding(PDB, elements);