From f8e663e8c9beff31e272d9aa88dfbbabbaa78193 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bastian=20M=C3=BCller?= <bastian@axiomzen.co>
Date: Wed, 4 May 2022 18:35:48 -0700
Subject: [PATCH] fix parsing of reference expressions: only parse casting
 expression

---
 runtime/parser2/expression.go                 |   7 +-
 runtime/parser2/expression_test.go            | 105 ++++++++++++++++++
 runtime/tests/checker/reference_test.go       |  20 ++++
 runtime/tests/interpreter/interpreter_test.go |  41 +++++++
 4 files changed, 170 insertions(+), 3 deletions(-)

diff --git a/runtime/parser2/expression.go b/runtime/parser2/expression.go
index c05c1816d9..274a282961 100644
--- a/runtime/parser2/expression.go
+++ b/runtime/parser2/expression.go
@@ -29,8 +29,10 @@ import (
 	"github.com/onflow/cadence/runtime/parser2/lexer"
 )
 
+const exprBindingPowerGap = 10
+
 const (
-	exprLeftBindingPowerTernary = 10 * (iota + 2)
+	exprLeftBindingPowerTernary = exprBindingPowerGap * (iota + 2)
 	exprLeftBindingPowerLogicalOr
 	exprLeftBindingPowerLogicalAnd
 	exprLeftBindingPowerComparison
@@ -1117,8 +1119,7 @@ func defineReferenceExpression() {
 		lexer.TokenAmpersand,
 		func(p *parser, token lexer.Token) ast.Expression {
 			p.skipSpaceAndComments(true)
-			// TODO: maybe require above unary
-			expression := parseExpression(p, lowestBindingPower)
+			expression := parseExpression(p, exprLeftBindingPowerCasting-exprBindingPowerGap)
 
 			p.skipSpaceAndComments(true)
 
diff --git a/runtime/parser2/expression_test.go b/runtime/parser2/expression_test.go
index 0e90e5f554..e34ceb1db2 100644
--- a/runtime/parser2/expression_test.go
+++ b/runtime/parser2/expression_test.go
@@ -1878,6 +1878,111 @@ func TestParseReference(t *testing.T) {
 	)
 }
 
+func TestParseNilCoelesceReference(t *testing.T) {
+
+	t.Parallel()
+
+	result, errs := ParseExpression(`
+          &xs["a"] as &Int? ?? 1
+        `)
+	require.Empty(t, errs)
+
+	utils.AssertEqualWithDiff(t,
+		&ast.BinaryExpression{
+			Operation: ast.OperationNilCoalesce,
+			Left: &ast.ReferenceExpression{
+				Expression: &ast.IndexExpression{
+					TargetExpression: &ast.IdentifierExpression{
+						Identifier: ast.Identifier{
+							Identifier: "xs",
+							Pos: ast.Position{
+								Offset: 12,
+								Line:   2,
+								Column: 11,
+							},
+						},
+					},
+					IndexingExpression: &ast.StringExpression{
+						Value: "a",
+						Range: ast.Range{
+							StartPos: ast.Position{
+								Offset: 15,
+								Line:   2,
+								Column: 14,
+							},
+							EndPos: ast.Position{
+								Offset: 17,
+								Line:   2,
+								Column: 16,
+							},
+						},
+					},
+					Range: ast.Range{
+						StartPos: ast.Position{
+							Offset: 14,
+							Line:   2,
+							Column: 13,
+						},
+						EndPos: ast.Position{
+							Offset: 18,
+							Line:   2,
+							Column: 17,
+						},
+					},
+				},
+				Type: &ast.OptionalType{
+					Type: &ast.ReferenceType{
+						Authorized: false,
+						Type: &ast.NominalType{
+							Identifier: ast.Identifier{
+								Identifier: "Int",
+								Pos: ast.Position{
+									Offset: 24,
+									Line:   2,
+									Column: 23,
+								},
+							},
+						},
+						StartPos: ast.Position{
+							Offset: 23,
+							Line:   2,
+							Column: 22,
+						},
+					},
+					EndPos: ast.Position{
+						Offset: 27,
+						Line:   2,
+						Column: 26,
+					},
+				},
+				StartPos: ast.Position{
+					Offset: 11,
+					Line:   2,
+					Column: 10,
+				},
+			},
+			Right: &ast.IntegerExpression{
+				PositiveLiteral: "1",
+				Value:           big.NewInt(1),
+				Base:            10,
+				Range: ast.Range{
+					StartPos: ast.Position{
+						Offset: 32,
+						Line:   2,
+						Column: 31,
+					},
+					EndPos: ast.Position{
+						Offset: 32,
+						Line:   2,
+						Column: 31,
+					},
+				},
+			},
+		},
+		result,
+	)
+}
+
 func TestParseCasts(t *testing.T) {
 
 	t.Parallel()
diff --git a/runtime/tests/checker/reference_test.go b/runtime/tests/checker/reference_test.go
index 7c9454517a..e86f6a58c1 100644
--- a/runtime/tests/checker/reference_test.go
+++ b/runtime/tests/checker/reference_test.go
@@ -1071,6 +1071,26 @@ func TestCheckReferenceExpressionOfOptional(t *testing.T) {
 	})
 }
 
+func TestCheckNilCoalesceReference(t *testing.T) {
+
+	t.Parallel()
+
+	checker, err := ParseAndCheckWithPanic(t, `
+      let xs = {"a": 1}
+      let ref = &xs["a"] as &Int? ?? panic("no a")
+    `)
+	require.NoError(t, err)
+
+	refValueType := RequireGlobalValue(t, checker.Elaboration, "ref")
+
+	assert.Equal(t,
+		&sema.ReferenceType{
+			Type: sema.IntType,
+		},
+		refValueType,
+	)
+}
+
 func TestCheckInvalidReferenceExpressionNonReferenceAmbiguous(t *testing.T) {
 
 	t.Parallel()
diff --git a/runtime/tests/interpreter/interpreter_test.go b/runtime/tests/interpreter/interpreter_test.go
index eff344fca9..a63d819012 100644
--- a/runtime/tests/interpreter/interpreter_test.go
+++ b/runtime/tests/interpreter/interpreter_test.go
@@ -9785,3 +9785,44 @@ func TestInterpretCastingBoxing(t *testing.T) {
 		)
 	})
 }
+
+func TestInterpretNilCoalesceReference(t *testing.T) {
+
+	t.Parallel()
+
+	standardLibraryFunctions :=
+		stdlib.StandardLibraryFunctions{
+			stdlib.PanicFunction,
+		}
+
+	valueDeclarations := standardLibraryFunctions.ToSemaValueDeclarations()
+	values := standardLibraryFunctions.ToInterpreterValueDeclarations()
+
+	inter, err := parseCheckAndInterpretWithOptions(t,
+		`
+          let xs = {"a": 2}
+          let ref = &xs["a"] as &Int? ?? panic("no a")
+        `,
+		ParseCheckAndInterpretOptions{
+			CheckerOptions: []sema.Option{
+				sema.WithPredeclaredValues(valueDeclarations),
+			},
+			Options: []interpreter.Option{
+				interpreter.WithPredeclaredValues(values),
+			},
+		},
+	)
+	require.NoError(t, err)
+
+	variable, ok := inter.Globals.Get("ref")
+	require.True(t, ok)
+
+	require.Equal(
+		t,
+		&interpreter.EphemeralReferenceValue{
+			Value:        interpreter.NewIntValueFromInt64(2),
+			BorrowedType: sema.IntType,
+		},
+		variable.GetValue(),
+	)
+}