[Constraint] Eliminate repetive locators to make useful information easier to read.

Author: Amritpan Kaur

include/swift/Sema/Constraint.h

@@ -852,7 +852,11 @@ class Constraint final : public llvm::ilist_node<Constraint>,
   /// Clone the given constraint.
   Constraint *clone(ConstraintSystem &cs) const;
 
-  void print(llvm::raw_ostream &Out, SourceManager *sm) const;
+  /// Prints constraint placed on type and constraint properties
+  ///
+  /// \c repeatedLocator checks if current locator is repeated in
+  /// preceding constraint and prevents repetitive locator printing.
+  void print(llvm::raw_ostream &Out, SourceManager *sm, bool repeatedLocator = false) const;
 
   SWIFT_DEBUG_DUMPER(dump(SourceManager *SM));
 

lib/Sema/Constraint.cpp

@@ -322,11 +322,12 @@ Constraint *Constraint::clone(ConstraintSystem &cs) const {
   llvm_unreachable("Unhandled ConstraintKind in switch.");
 }
 
-void Constraint::print(llvm::raw_ostream &Out, SourceManager *sm) const {
+void Constraint::print(llvm::raw_ostream &Out, SourceManager *sm, bool repeatedLocator) const {
   // Print all type variables as $T0 instead of _ here.
   PrintOptions PO;
   PO.PrintTypesForDebugging = true;
 
+  ConstraintLocator *firstLocator;
   if (Kind == ConstraintKind::Disjunction ||
       Kind == ConstraintKind::Conjunction) {
     Out << (Kind == ConstraintKind::Disjunction ? "disjunction"
@@ -337,6 +338,7 @@ void Constraint::print(llvm::raw_ostream &Out, SourceManager *sm) const {
     if (isIsolated())
       Out << " (isolated)";
 
+    firstLocator = Locator;
     if (Locator) {
       Out << " [[";
       Locator->dump(sm, Out);
@@ -352,7 +354,11 @@ void Constraint::print(llvm::raw_ostream &Out, SourceManager *sm) const {
                    Out << ">  [favored]  ";
                  else
                    Out << ">             ";
+                 if (constraint->getLocator() == firstLocator) {
+                   constraint->print(Out, sm, true);
+                 } else {
                  constraint->print(Out, sm);
+                 }
                },
                [&] { Out << "\n"; });
     return;
@@ -522,7 +528,7 @@ void Constraint::print(llvm::raw_ostream &Out, SourceManager *sm) const {
     fix->print(Out);
   }
 
-  if (Locator) {
+  if (Locator && !repeatedLocator) {
     Out << " [[";
     Locator->dump(sm, Out);
     Out << "]];";