Merge pull request #26149 from theblixguy/fix/SR-11134

[Parser] Diagnose use of subscript inside an array literal

Author: jrose-apple

include/swift/AST/DiagnosticsParse.def

@@ -762,6 +762,13 @@ ERROR(extra_rbracket,PointsToFirstBadToken,
       "unexpected ']' in type; did you mean to write an array type?", ())
 ERROR(extra_colon,PointsToFirstBadToken,
       "unexpected ':' in type; did you mean to write a dictionary type?", ())
+WARNING(subscript_array_element, none,
+        "unexpected subscript in array literal; did you mean to write two "
+        "separate elements instead?", ())
+NOTE(subscript_array_element_fix_it_add_comma, none, "add a separator between "
+     "the elements", ())
+NOTE(subscript_array_element_fix_it_remove_space, none,
+     "remove the space between the elements to silence this warning", ())
 
 // Tuple Types
 ERROR(expected_rparen_tuple_type_list,none,

include/swift/Parse/Parser.h

@@ -1435,6 +1435,8 @@ class Parser {
 
   UnresolvedDeclRefExpr *parseExprOperator();
 
+  void validateCollectionElement(ParserResult<Expr> element);
+
   //===--------------------------------------------------------------------===//
   // Statement Parsing
 

lib/Parse/ParseExpr.cpp

@@ -3447,8 +3447,10 @@ Parser::parseExprCollectionElement(Optional<bool> &isDictionary) {
   if (!isDictionary.hasValue())
     isDictionary = Tok.is(tok::colon);
 
-  if (!*isDictionary)
+  if (!*isDictionary) {
+    validateCollectionElement(Element);
     return Element;
+  }
 
   if (Element.isNull())
     return Element;
@@ -3471,6 +3473,43 @@ Parser::parseExprCollectionElement(Optional<bool> &isDictionary) {
       TupleExpr::createImplicit(Context, {Element.get(), Value.get()}, {}));
 }
 
+/// validateCollectionElement - Check if a given collection element is valid.
+///
+/// At the moment, this checks whether a given collection element is a subscript
+/// expression and whether we're subscripting into an array. If we are, then it
+/// we emit a diagnostic in case it was not something that the user was
+/// expecting.
+///
+/// For example: `let array [ [0, 1] [42] ]`
+void Parser::validateCollectionElement(ParserResult<Expr> element) {
+  if (element.isNull())
+    return;
+
+  auto elementExpr = element.get();
+  if (!isa<SubscriptExpr>(elementExpr))
+    return;
+
+  auto subscriptExpr = cast<SubscriptExpr>(elementExpr);
+  if (!isa<ArrayExpr>(subscriptExpr->getBase()))
+    return;
+
+  auto arrayExpr = cast<ArrayExpr>(subscriptExpr->getBase());
+
+  auto startLocOfSubscript = subscriptExpr->getIndex()->getStartLoc();
+  auto endLocOfArray = arrayExpr->getEndLoc();
+  auto locForEndOfTokenArray = L->getLocForEndOfToken(SourceMgr, endLocOfArray);
+
+  if (locForEndOfTokenArray != startLocOfSubscript) {
+    auto subscriptLoc = subscriptExpr->getLoc();
+    diagnose(subscriptLoc, diag::subscript_array_element)
+        .highlight(subscriptExpr->getSourceRange());
+    diagnose(subscriptLoc, diag::subscript_array_element_fix_it_add_comma)
+        .fixItInsertAfter(endLocOfArray, ",");
+    diagnose(subscriptLoc, diag::subscript_array_element_fix_it_remove_space)
+        .fixItRemoveChars(locForEndOfTokenArray, startLocOfSubscript);
+  }
+}
+
 void Parser::addPatternVariablesToScope(ArrayRef<Pattern *> Patterns) {
   for (Pattern *Pat : Patterns) {
     Pat->forEachVariable([&](VarDecl *VD) {

test/type/array.swift

@@ -114,3 +114,14 @@ func passAssocType<T : HasAssocType>(_ t: T) {
   takesAssocType(t, [T.A](), [T.A?]())
 }
 
+// SR-11134
+
+let sr_11134_1 = [[1, 2, 3][0]] // ok
+let sr_11134_2 = [[1, 2, 3] [1]] // expected-warning {{unexpected subscript in array literal; did you mean to write two separate elements instead?}}
+// expected-note@-1 {{add a separator between the elements}}{{28-28=,}}
+// expected-note@-2 {{remove the space between the elements to silence this warning}}{{28-29=}}
+let sr_11134_3 = [
+  [1, 2, 3] [1] // expected-warning {{unexpected subscript in array literal; did you mean to write two separate elements instead?}}
+// expected-note@-1 {{add a separator between the elements}}{{12-12=,}}
+// expected-note@-2 {{remove the space between the elements to silence this warning}}{{12-13=}}
+]