[Sema] Add a solution callback that is called when the constraint system produces a solution

When doing solver-based cursor info, we’ll type check the expression in question using a normal `typeCheckASTNodeAtLoc` call (not in code completion mode) and listen for any solutions that were produced during the type check.

Author: ahoppen

include/swift/AST/ASTContext.h

@@ -289,6 +289,11 @@ class ASTContext final {
 
   ide::TypeCheckCompletionCallback *CompletionCallback = nullptr;
 
+  /// A callback that will be called when the constraint system found a
+  /// solution. Called multiple times if the constraint system has ambiguous
+  /// solutions.
+  ide::TypeCheckCompletionCallback *SolutionCallback = nullptr;
+
   /// The request-evaluator that is used to process various requests.
   Evaluator evaluator;
 

lib/Sema/CSSolver.cpp

@@ -1353,6 +1353,24 @@ Optional<std::vector<Solution>> ConstraintSystem::solve(
     }
   };
 
+  auto reportSolutionsToSolutionCallback = [&](const SolutionResult &result) {
+    if (!getASTContext().SolutionCallback) {
+      return;
+    }
+    switch (result.getKind()) {
+    case SolutionResult::Success:
+      getASTContext().SolutionCallback->sawSolution(result.getSolution());
+      break;
+    case SolutionResult::Ambiguous:
+      for (auto &solution : result.getAmbiguousSolutions()) {
+        getASTContext().SolutionCallback->sawSolution(solution);
+      }
+      break;
+    default:
+      break;
+    }
+  };
+
   // Take up to two attempts at solving the system. The first attempts to
   // solve a system that is expected to be well-formed, the second kicks in
   // when there is an error and attempts to salvage an ill-formed program.
@@ -1365,6 +1383,7 @@ Optional<std::vector<Solution>> ConstraintSystem::solve(
     case SolutionResult::Success: {
       // Return the successful solution.
       dumpSolutions(solution);
+      reportSolutionsToSolutionCallback(solution);
       std::vector<Solution> result;
       result.push_back(std::move(solution).takeSolution());
       return std::move(result);
@@ -1394,6 +1413,7 @@ Optional<std::vector<Solution>> ConstraintSystem::solve(
       // If salvaging produced an ambiguous result, it has already been
       // diagnosed.
       if (stage == 1) {
+        reportSolutionsToSolutionCallback(solution);
         solution.markAsDiagnosed();
         return None;
       }
@@ -1412,12 +1432,14 @@ Optional<std::vector<Solution>> ConstraintSystem::solve(
 
     case SolutionResult::UndiagnosedError:
       if (shouldSuppressDiagnostics()) {
+        reportSolutionsToSolutionCallback(solution);
         solution.markAsDiagnosed();
         return None;
       }
 
       if (stage == 1) {
         diagnoseFailureFor(target);
+        reportSolutionsToSolutionCallback(solution);
         solution.markAsDiagnosed();
         return None;
       }