Revert "[code-completion] Disable diagnostics in @functionBuilder bodies"

This reverts commit c6eade1.

Author: rintaro

include/swift/Basic/SourceManager.h

@@ -103,13 +103,6 @@ class SourceManager {
            rangeContainsTokenLoc(Enclosing, Inner.End);
   }
 
-  /// Returns true if range \p R contains the code-completion location, if any.
-  bool rangeContainsCodeCompletionLoc(SourceRange R) const {
-    return CodeCompletionBufferID
-               ? rangeContainsTokenLoc(R, getCodeCompletionLoc())
-               : false;
-  }
-
   /// Returns the buffer ID for the specified *valid* location.
   ///
   /// Because a valid source location always corresponds to a source buffer,

lib/Sema/BuilderTransform.cpp

@@ -566,12 +566,6 @@ ConstraintSystem::TypeMatchResult ConstraintSystem::applyFunctionBuilder(
     assert(!builderType->hasTypeParameter());
   }
 
-  // If we are performing code-completion inside the closure body, supress
-  // diagnostics to workaround typechecking performance problems.
-  if (getASTContext().SourceMgr.rangeContainsCodeCompletionLoc(
-          closure->getSourceRange()))
-    Options |= ConstraintSystemFlags::SuppressDiagnostics;
-
   BuilderClosureVisitor visitor(getASTContext(), this,
                                 /*wantExpr=*/true, builderType);
   Expr *singleExpr = visitor.visit(closure->getBody());