Shallow now handles strings as well

Add clarifications for string/slice cases.

Signed-off-by: Maxime Soulé <btik-git@scoubidou.com>

cmp_funcs_test.go

@@ -1557,6 +1557,42 @@ func ExampleCmpShallow() {
 	// false
 }
 
+func ExampleCmpShallow_slice() {
+	t := &testing.T{}
+
+	back := []int{1, 2, 3, 1, 2, 3}
+	a := back[:3]
+	b := back[3:]
+
+	ok := CmpShallow(t, a, back)
+	fmt.Println("are ≠ but share the same area:", ok)
+
+	ok = CmpShallow(t, b, back)
+	fmt.Println("are = but do not point to same area:", ok)
+
+	// Output:
+	// are ≠ but share the same area: true
+	// are = but do not point to same area: false
+}
+
+func ExampleCmpShallow_string() {
+	t := &testing.T{}
+
+	back := "foobarfoobar"
+	a := back[:6]
+	b := back[6:]
+
+	ok := CmpShallow(t, a, back)
+	fmt.Println("are ≠ but share the same area:", ok)
+
+	ok = CmpShallow(t, b, a)
+	fmt.Println("are = but do not point to same area:", ok)
+
+	// Output:
+	// are ≠ but share the same area: true
+	// are = but do not point to same area: false
+}
+
 func ExampleCmpSlice_slice() {
 	t := &testing.T{}
 

example_test.go

@@ -1624,6 +1624,42 @@ func ExampleShallow() {
 	// false
 }
 
+func ExampleShallow_slice() {
+	t := &testing.T{}
+
+	back := []int{1, 2, 3, 1, 2, 3}
+	a := back[:3]
+	b := back[3:]
+
+	ok := CmpDeeply(t, a, Shallow(back))
+	fmt.Println("are ≠ but share the same area:", ok)
+
+	ok = CmpDeeply(t, b, Shallow(back))
+	fmt.Println("are = but do not point to same area:", ok)
+
+	// Output:
+	// are ≠ but share the same area: true
+	// are = but do not point to same area: false
+}
+
+func ExampleShallow_string() {
+	t := &testing.T{}
+
+	back := "foobarfoobar"
+	a := back[:6]
+	b := back[6:]
+
+	ok := CmpDeeply(t, a, Shallow(back))
+	fmt.Println("are ≠ but share the same area:", ok)
+
+	ok = CmpDeeply(t, b, Shallow(a))
+	fmt.Println("are = but do not point to same area:", ok)
+
+	// Output:
+	// are ≠ but share the same area: true
+	// are = but do not point to same area: false
+}
+
 func ExampleSlice_slice() {
 	t := &testing.T{}
 

t_test.go

@@ -1557,6 +1557,42 @@ func ExampleT_Shallow() {
 	// false
 }
 
+func ExampleT_Shallow_slice() {
+	t := NewT(&testing.T{})
+
+	back := []int{1, 2, 3, 1, 2, 3}
+	a := back[:3]
+	b := back[3:]
+
+	ok := t.Shallow(a, back)
+	fmt.Println("are ≠ but share the same area:", ok)
+
+	ok = t.Shallow(b, back)
+	fmt.Println("are = but do not point to same area:", ok)
+
+	// Output:
+	// are ≠ but share the same area: true
+	// are = but do not point to same area: false
+}
+
+func ExampleT_Shallow_string() {
+	t := NewT(&testing.T{})
+
+	back := "foobarfoobar"
+	a := back[:6]
+	b := back[6:]
+
+	ok := t.Shallow(a, back)
+	fmt.Println("are ≠ but share the same area:", ok)
+
+	ok = t.Shallow(b, a)
+	fmt.Println("are = but do not point to same area:", ok)
+
+	// Output:
+	// are ≠ but share the same area: true
+	// are = but do not point to same area: false
+}
+
 func ExampleT_Slice_slice() {
 	t := NewT(&testing.T{})
 

td_shallow.go

@@ -9,6 +9,7 @@ package testdeep
 import (
 	"fmt"
 	"reflect"
+	"unsafe"
 
 	"github.com/maxatome/go-testdeep/internal/ctxerr"
 	"github.com/maxatome/go-testdeep/internal/types"
@@ -18,20 +19,44 @@ type tdShallow struct {
 	Base
 	expectedKind    reflect.Kind
 	expectedPointer uintptr
+	expectedStr     string // in reflect.String case, to avoid contents  GC
 }
 
 var _ TestDeep = &tdShallow{}
 
+func stringPointer(s string) uintptr {
+	return (*reflect.StringHeader)(unsafe.Pointer(&s)).Data
+}
+
 // Shallow operator compares pointers only, not their contents. It
 // applies on channels, functions (with some restrictions), maps,
-// pointers and slices.
+// pointers, slices and strings.
 //
 // During a match, the compared data must be the same as
 // "expectedPointer" to succeed.
 //
 //   a, b := 123, 123
 //   CmpDeeply(t, &a, Shallow(&a)) // succeeds
 //   CmpDeeply(t, &a, Shallow(&b)) // fails even if a == b as &a != &b
+//
+//   back := "foobarfoobar"
+//   a, b := back[:6], back[6:]
+//   // a == b but...
+//   CmpDeeply(t, &a, Shallow(&b)) // fails
+//
+// Be careful for slices and strings! Shallow can succeed but the
+// slices/strings not be identical because of their different
+// lengths. For example:
+//
+//   a := "foobar yes!"
+//   b := a[:1]                    // aka. "f"
+//   CmpDeeply(t, &a, Shallow(&b)) // succeeds as both strings point to the same area, even if len() differ
+//
+// The same behavior occurs for slices:
+//
+//   a := []int{1, 2, 3, 4, 5, 6}
+//   b := a[:2]                    // aka. []int{1, 2}
+//   CmpDeeply(t, &a, Shallow(&b)) // succeeds as both slices point to the same area, even if len() differ
 func Shallow(expectedPtr interface{}) TestDeep {
 	vptr := reflect.ValueOf(expectedPtr)
 
@@ -56,8 +81,13 @@ func Shallow(expectedPtr interface{}) TestDeep {
 		shallow.expectedPointer = vptr.Pointer()
 		return &shallow
 
+	case reflect.String:
+		shallow.expectedStr = vptr.String()
+		shallow.expectedPointer = stringPointer(shallow.expectedStr)
+		return &shallow
+
 	default:
-		panic("usage: Shallow(CHANNEL|FUNC|MAP|PTR|SLICE|UNSAFE_PTR)")
+		panic("usage: Shallow(CHANNEL|FUNC|MAP|PTR|SLICE|UNSAFE_PTR|STRING)")
 	}
 }
 
@@ -73,13 +103,22 @@ func (s *tdShallow) Match(ctx ctxerr.Context, got reflect.Value) *ctxerr.Error {
 		})
 	}
 
-	if got.Pointer() != s.expectedPointer {
+	var ptr uintptr
+
+	// Special case for strings
+	if s.expectedKind == reflect.String {
+		ptr = stringPointer(got.String())
+	} else {
+		ptr = got.Pointer()
+	}
+
+	if ptr != s.expectedPointer {
 		if ctx.BooleanError {
 			return ctxerr.BooleanError
 		}
 		return ctx.CollectError(&ctxerr.Error{
 			Message:  fmt.Sprintf("%s pointer mismatch", s.expectedKind),
-			Got:      types.RawString(fmt.Sprintf("0x%x", got.Pointer())),
+			Got:      types.RawString(fmt.Sprintf("0x%x", ptr)),
 			Expected: types.RawString(fmt.Sprintf("0x%x", s.expectedPointer)),
 		})
 	}

td_shallow_test.go

@@ -17,18 +17,18 @@ import (
 func TestShallow(t *testing.T) {
 	//
 	// Slice
-	gotSlice := []int{1, 2, 3}
-	expectedSlice := []int{1, 2, 3}
-	checkError(t, gotSlice, testdeep.Shallow(expectedSlice),
+	back := [...]int{1, 2, 3, 1, 2, 3}
+	as := back[:3]
+	bs := back[3:]
+	checkError(t, bs, testdeep.Shallow(back[:]),
 		expectedError{
 			Message:  mustBe("slice pointer mismatch"),
 			Path:     mustBe("DATA"),
 			Got:      mustContain("0x"),
 			Expected: mustContain("0x"),
 		})
 
-	expectedSlice = gotSlice
-	checkOK(t, gotSlice, testdeep.Shallow(expectedSlice))
+	checkOK(t, as, testdeep.Shallow(back[:]))
 	checkOK(t, ([]byte)(nil), ([]byte)(nil))
 
 	//
@@ -98,6 +98,30 @@ func TestShallow(t *testing.T) {
 	checkOK(t, gotChan, testdeep.Shallow(expectedChan))
 	checkOK(t, (chan int)(nil), (chan int)(nil))
 
+	//
+	// String
+	backStr := "foobarfoobar!"
+	a := backStr[:6]
+	b := backStr[6:12]
+	checkOK(t, a, testdeep.Shallow(backStr))
+	checkOK(t, backStr, testdeep.Shallow(a))
+	checkOK(t, b, testdeep.Shallow(backStr[6:7]))
+
+	checkError(t, backStr, testdeep.Shallow(b),
+		expectedError{
+			Message:  mustBe("string pointer mismatch"),
+			Path:     mustBe("DATA"),
+			Got:      mustContain("0x"),
+			Expected: mustContain("0x"),
+		})
+	checkError(t, b, testdeep.Shallow(backStr),
+		expectedError{
+			Message:  mustBe("string pointer mismatch"),
+			Path:     mustBe("DATA"),
+			Got:      mustContain("0x"),
+			Expected: mustContain("0x"),
+		})
+
 	//
 	// Erroneous mix
 	checkError(t, gotMap, testdeep.Shallow(expectedChan),
@@ -110,7 +134,7 @@ func TestShallow(t *testing.T) {
 
 	//
 	// Bad usage
-	test.CheckPanic(t, func() { testdeep.Shallow("test") }, "usage: Shallow")
+	test.CheckPanic(t, func() { testdeep.Shallow(42) }, "usage: Shallow")
 
 	//
 	//