test: add more tests for const decls with ommitted RHS expressions

Add analogous tests to go/types and types2 test suites.
Make sure "assert" built-in is available in type-checker
tests.

For #49157.
For #53585.

Change-Id: I092901ecb43eb4833c09bd8f5e38efbe0285babe
Reviewed-on: https://go-review.googlesource.com/c/go/+/414795
Run-TryBot: Robert Griesemer <gri@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

src/cmd/compile/internal/types2/check_test.go

@@ -297,7 +297,7 @@ func TestManual(t *testing.T) {
 
 // TODO(gri) go/types has extra TestLongConstants and TestIndexRepresentability tests
 
-func TestCheck(t *testing.T)     { testDirFiles(t, "testdata/check", 55, false) } // TODO(gri) narrow column tolerance
+func TestCheck(t *testing.T)     { DefPredeclaredTestFuncs(); testDirFiles(t, "testdata/check", 55, false) } // TODO(gri) narrow column tolerance
 func TestSpec(t *testing.T)      { testDirFiles(t, "testdata/spec", 0, false) }
 func TestExamples(t *testing.T)  { testDirFiles(t, "testdata/examples", 0, false) }
 func TestFixedbugs(t *testing.T) { testDirFiles(t, "testdata/fixedbugs", 0, false) }

src/cmd/compile/internal/types2/testdata/check/constdecl.go

@@ -135,4 +135,26 @@ const (
 	f // ERROR invalid array length
 )
 
+// Test that identifiers in implicit (omitted) RHS
+// expressions of constant declarations are resolved
+// in the correct context; see issues #49157, #53585.
+const X = 2
+
+func _() {
+	const (
+		A    = iota // 0
+		iota = iota // 1
+		B           // 1 (iota is declared locally on prev. line)
+		C           // 1
+	)
+	assert(A == 0 && B == 1 && C == 1)
+
+	const (
+		X = X + X
+		Y
+		Z = iota
+	)
+	assert(X == 4 && Y == 8 && Z == 1)
+}
+
 // TODO(gri) move extra tests from testdata/const0.src into here

src/go/types/check_test.go

@@ -372,7 +372,7 @@ func TestIssue47243_TypedRHS(t *testing.T) {
 	testFiles(t, &StdSizes{4, 4}, []string{"p.go"}, [][]byte{[]byte(src)}, false, nil)
 }
 
-func TestCheck(t *testing.T)     { testDirFiles(t, "testdata/check", false) }
+func TestCheck(t *testing.T)     { DefPredeclaredTestFuncs(); testDirFiles(t, "testdata/check", false) }
 func TestSpec(t *testing.T)      { testDirFiles(t, "testdata/spec", false) }
 func TestExamples(t *testing.T)  { testDirFiles(t, "testdata/examples", false) }
 func TestFixedbugs(t *testing.T) { testDirFiles(t, "testdata/fixedbugs", false) }

src/go/types/testdata/check/constdecl.go

@@ -138,4 +138,26 @@ const (
 	f // ERROR invalid array length
 )
 
+// Test that identifiers in implicit (omitted) RHS
+// expressions of constant declarations are resolved
+// in the correct context; see issues #49157, #53585.
+const X = 2
+
+func _() {
+	const (
+		A    = iota // 0
+		iota = iota // 1
+		B           // 1 (iota is declared locally on prev. line)
+		C           // 1
+	)
+	assert(A == 0 && B == 1 && C == 1)
+
+	const (
+		X = X + X
+		Y
+		Z = iota
+	)
+	assert(X == 4 && Y == 8 && Z == 1)
+}
+
 // TODO(gri) move extra tests from testdata/const0.src into here

test/const8.go

@@ -0,0 +1,36 @@
+// run
+
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Test that identifiers in implicit (omitted) RHS
+// expressions of constant declarations are resolved
+// in the correct context; see issues #49157, #53585.
+
+package main
+
+const X = 2
+
+func main() {
+	const (
+		A    = iota // 0
+		iota = iota // 1
+		B           // 1 (iota is declared locally on prev. line)
+		C           // 1
+	)
+	if A != 0 || B != 1 || C != 1 {
+		println("got", A, B, C, "want 0 1 1")
+		panic("FAILED")
+	}
+
+	const (
+		X = X + X
+		Y
+		Z = iota
+	)
+	if X != 4 || Y != 8 || Z != 1 {
+		println("got", X, Y, Z, "want 4 8 1")
+		panic("FAILED")
+	}
+}