[Constraint system] Lift PatternBindingDecl into SolutionApplicationTarget

lib/Sema/BuilderTransform.cpp

@@ -269,26 +269,12 @@ class BuilderClosureVisitor
       return;
     }
 
-    // If we aren't generating constraints, there's nothing to do.
-    if (!cs)
-      return;
-
-    /// Generate constraints for each pattern binding entry
-    for (unsigned index : range(patternBinding->getNumPatternEntries())) {
-      // Type check the pattern.
-      auto pattern = patternBinding->getPattern(index);
-      auto contextualPattern = ContextualPattern::forRawPattern(pattern, dc);
-      Type patternType = TypeChecker::typeCheckPattern(contextualPattern);
-
-      // Generate constraints for the initialization.
-      auto target = SolutionApplicationTarget::forInitialization(
-          patternBinding->getInit(index), dc, patternType, pattern,
-          /*bindPatternVarsOneWay=*/true);
+    // If there is a constraint system, generate constraints for the pattern
+    // binding.
+    if (cs) {
+      SolutionApplicationTarget target(patternBinding);
       if (cs->generateConstraints(target, FreeTypeVariableBinding::Disallow))
-        continue;
-
-      // Keep track of this binding entry.
-      applied.patternBindingEntries.insert({{patternBinding, index}, target});
+        hadError = true;
     }
   }
 
@@ -1035,11 +1021,11 @@ class BuilderClosureRewriter
     for (unsigned index : range(patternBinding->getNumPatternEntries())) {
       // Find the solution application target for this.
       auto knownTarget =
-          builderTransform.patternBindingEntries.find({patternBinding, index});
-      assert(knownTarget != builderTransform.patternBindingEntries.end());
+          *solution.getConstraintSystem().getSolutionApplicationTarget(
+            {patternBinding, index});
 
       // Rewrite the target.
-      auto resultTarget = rewriteTarget(knownTarget->second);
+      auto resultTarget = rewriteTarget(knownTarget);
       if (!resultTarget)
         continue;
 

lib/Sema/CSApply.cpp

@@ -8103,6 +8103,25 @@ ExprWalker::rewriteTarget(SolutionApplicationTarget target) {
       solution.setExprTypes(guardExpr);
     }
 
+    return target;
+  } else if (auto patternBinding = target.getAsPatternBinding()) {
+    ConstraintSystem &cs = solution.getConstraintSystem();
+    for (unsigned index : range(patternBinding->getNumPatternEntries())) {
+      // Find the solution application target for this.
+      auto knownTarget = *cs.getSolutionApplicationTarget(
+          {patternBinding, index});
+
+      // Rewrite the target.
+      auto resultTarget = rewriteTarget(knownTarget);
+      if (!resultTarget)
+        return None;
+
+      patternBinding->setPattern(
+          index, resultTarget->getInitializationPattern(),
+          resultTarget->getDeclContext());
+      patternBinding->setInit(index, resultTarget->getAsExpr());
+    }
+
     return target;
   } else {
     auto fn = *target.getAsFunction();
@@ -8380,6 +8399,10 @@ SolutionApplicationTarget SolutionApplicationTarget::walk(ASTWalker &walker) {
     }
 
     return *this;
+
+  case Kind::patternBinding:
+    return *this;
   }
+
   llvm_unreachable("invalid target kind");
 }

lib/Sema/CSGen.cpp

@@ -4428,7 +4428,48 @@ bool ConstraintSystem::generateConstraints(
     return false;
   }
 
-  llvm_unreachable("BOOM");
+  switch (target.kind) {
+  case SolutionApplicationTarget::Kind::expression:
+    llvm_unreachable("Handled above");
+
+  case SolutionApplicationTarget::Kind::caseLabelItem:
+  case SolutionApplicationTarget::Kind::function:
+  case SolutionApplicationTarget::Kind::stmtCondition:
+    llvm_unreachable("Handled separately");
+
+  case SolutionApplicationTarget::Kind::patternBinding: {
+    auto patternBinding = target.getAsPatternBinding();
+    auto dc = target.getDeclContext();
+    bool hadError = false;
+
+    /// Generate constraints for each pattern binding entry
+    for (unsigned index : range(patternBinding->getNumPatternEntries())) {
+      // Type check the pattern.
+      auto pattern = patternBinding->getPattern(index);
+      auto contextualPattern = ContextualPattern::forRawPattern(pattern, dc);
+      Type patternType = TypeChecker::typeCheckPattern(contextualPattern);
+
+      auto init = patternBinding->getInit(index);
+      if (!init) {
+        llvm_unreachable("Unsupported pattern binding entry");
+      }
+
+      // Generate constraints for the initialization.
+      auto target = SolutionApplicationTarget::forInitialization(
+          init, dc, patternType, pattern,
+          /*bindPatternVarsOneWay=*/true);
+      if (generateConstraints(target, FreeTypeVariableBinding::Disallow)) {
+        hadError = true;
+        continue;
+      }
+
+      // Keep track of this binding entry.
+      setSolutionApplicationTarget({patternBinding, index}, target);
+    }
+
+    return hadError;
+  }
+  }
 }
 
 Expr *ConstraintSystem::generateConstraints(