[ConstraintSystem] Use affected range (if any) to diagnose 'too complex' failures

(cherry picked from commit a40e8e8)

Author: xedin

include/swift/Sema/SolutionResult.h

@@ -64,6 +64,9 @@ class SolutionResult {
   /// \c numSolutions entries.
   Solution *solutions = nullptr;
 
+  /// A source range that was too complex to solve.
+  Optional<SourceRange> TooComplexAt = None;
+
   /// General constructor for the named constructors.
   SolutionResult(Kind kind) : kind(kind) {
     emittedDiagnostic = false;
@@ -95,9 +98,7 @@ class SolutionResult {
 
   /// Produce a "too complex" failure, which was not yet been
   /// diagnosed.
-  static SolutionResult forTooComplex() {
-    return SolutionResult(TooComplex);
-  }
+  static SolutionResult forTooComplex(Optional<SourceRange> affected);
 
   /// Produce a failure that has already been diagnosed.
   static SolutionResult forError() {
@@ -123,6 +124,10 @@ class SolutionResult {
   /// Take the set of solutions when there is an ambiguity.
   MutableArrayRef<Solution> takeAmbiguousSolutions() &&;
 
+  /// Retrieve a range of source that has been determined to be too
+  /// complex to solve in a reasonable time.
+  Optional<SourceRange> getTooComplexAt() const { return TooComplexAt; }
+
   /// Whether this solution requires the client to produce a diagnostic.
   bool requiresDiagnostic() const {
     switch (kind) {

lib/Sema/CSApply.cpp

@@ -9145,6 +9145,12 @@ SolutionResult SolutionResult::forAmbiguous(
   return result;
 }
 
+SolutionResult SolutionResult::forTooComplex(Optional<SourceRange> affected) {
+  SolutionResult result(Kind::TooComplex);
+  result.TooComplexAt = affected;
+  return result;
+}
+
 SolutionResult::~SolutionResult() {
   assert((!requiresDiagnostic() || emittedDiagnostic) &&
          "SolutionResult was destroyed without emitting a diagnostic");

lib/Sema/CSSolver.cpp

@@ -1298,12 +1298,21 @@ Optional<std::vector<Solution>> ConstraintSystem::solve(
       maybeProduceFallbackDiagnostic(target);
       return None;
 
-    case SolutionResult::TooComplex:
-      getASTContext().Diags.diagnose(
-          target.getLoc(), diag::expression_too_complex)
-            .highlight(target.getSourceRange());
+    case SolutionResult::TooComplex: {
+      auto affectedRange = solution.getTooComplexAt();
+
+      // If affected range is unknown, let's use whole
+      // target.
+      if (!affectedRange)
+        affectedRange = target.getSourceRange();
+
+      getASTContext()
+          .Diags.diagnose(affectedRange->Start, diag::expression_too_complex)
+          .highlight(*affectedRange);
+
       solution.markAsDiagnosed();
       return None;
+    }
 
     case SolutionResult::Ambiguous:
       // If salvaging produced an ambiguous result, it has already been
@@ -1375,7 +1384,7 @@ ConstraintSystem::solveImpl(SolutionApplicationTarget &target,
   solve(solutions, allowFreeTypeVariables);
 
   if (isTooComplex(solutions))
-    return SolutionResult::forTooComplex();
+    return SolutionResult::forTooComplex(getTooComplexRange());
 
   switch (solutions.size()) {
   case 0:

lib/Sema/ConstraintSystem.cpp

@@ -3784,7 +3784,7 @@ SolutionResult ConstraintSystem::salvage() {
   }
 
   if (isTooComplex(viable))
-    return SolutionResult::forTooComplex();
+    return SolutionResult::forTooComplex(getTooComplexRange());
 
   // Could not produce a specific diagnostic; punt to the client.
   return SolutionResult::forUndiagnosedError();

validation-test/Sema/type_checker_perf/slow/rdar19612086.swift

@@ -11,12 +11,11 @@ struct rdar19612086 {
   let x = 1.0
 
   var description : String {
-    return "\(i)" + Stringly(format: "%.2f", x) +
+    return "\(i)" + Stringly(format: "%.2f", x) +   // expected-error {{reasonable time}}
            "\(i+1)" + Stringly(format: "%.2f", x) +
            "\(i+2)" + Stringly(format: "%.2f", x) +
            "\(i+3)" + Stringly(format: "%.2f", x) +
            "\(i+4)" + Stringly(format: "%.2f", x) +
            "\(i+5)" + Stringly(format: "%.2f", x)
-    // expected-error@-1 {{reasonable time}}
   }
 }

validation-test/Sema/type_checker_perf/slow/rdar22079400.swift

@@ -1,9 +1,8 @@
 // RUN: %target-typecheck-verify-swift -solver-expression-time-threshold=1
 // REQUIRES: tools-release,no_asan
 
-let _ = (0...1).lazy.flatMap {
+let _ = (0...1).lazy.flatMap { // expected-error {{reasonable time}}
   a in (1...2).lazy.map { b in (a, b) }
 }.filter {
-  // expected-error@-1 {{reasonable time}}
   1 < $0 && $0 < $1 && $0 + $1 < 3
 }