[ConstraintSystem] Augment solution application target to support expression patterns

Author: xedin

include/swift/Sema/ConstraintSystem.h

@@ -1715,6 +1715,13 @@ class SolutionApplicationTarget {
                             ContextualTypePurpose contextualPurpose,
                             TypeLoc convertType, bool isDiscarded);
 
+  SolutionApplicationTarget(Expr *expr, DeclContext *dc, ExprPattern *pattern,
+                            Type patternType)
+      : SolutionApplicationTarget(expr, dc, CTP_ExprPattern, patternType,
+                                  /*isDiscarded=*/false) {
+    setPattern(pattern);
+  }
+
   SolutionApplicationTarget(AnyFunctionRef fn)
       : SolutionApplicationTarget(fn, fn.getBody()) { }
 
@@ -1800,6 +1807,12 @@ class SolutionApplicationTarget {
   static SolutionApplicationTarget forPropertyWrapperInitializer(
       VarDecl *wrappedVar, DeclContext *dc, Expr *initializer);
 
+  static SolutionApplicationTarget forExprPattern(Expr *expr, DeclContext *dc,
+                                                  ExprPattern *pattern,
+                                                  Type patternTy) {
+    return {expr, dc, pattern, patternTy};
+  }
+
   Expr *getAsExpr() const {
     switch (kind) {
     case Kind::expression:
@@ -1902,6 +1915,12 @@ class SolutionApplicationTarget {
     return expression.pattern;
   }
 
+  ExprPattern *getExprPattern() const {
+    assert(kind == Kind::expression);
+    assert(expression.contextualPurpose == CTP_ExprPattern);
+    return cast<ExprPattern>(expression.pattern);
+  }
+
   /// For a pattern initialization target, retrieve the contextual pattern.
   ContextualPattern getContextualPattern() const;
 
@@ -2022,7 +2041,8 @@ class SolutionApplicationTarget {
     assert(kind == Kind::expression);
     assert(expression.contextualPurpose == CTP_Initialization ||
            expression.contextualPurpose == CTP_ForEachStmt ||
-           expression.contextualPurpose == CTP_ForEachSequence);
+           expression.contextualPurpose == CTP_ForEachSequence ||
+           expression.contextualPurpose == CTP_ExprPattern);
     expression.pattern = pattern;
   }