Merge #151740

151740: sql: remove LTREE prev logic r=paulniziolek a=paulniziolek

This was not needed & was incorrect, messing up LTREE comparisons. We should only rely on LTREE's `Compare` method.

Informs: #44657
Epic: CRDB-148

Release note: None

Co-authored-by: Paul Niziolek <[email protected]>

Author: craig[bot]

pkg/sql/sem/tree/datum.go

@@ -4547,11 +4547,7 @@ func (d *DLTree) Compare(ctx context.Context, cmpCtx CompareContext, other Datum
 
 // Prev implements the Datum interface.
 func (d *DLTree) Prev(ctx context.Context, cmpCtx CompareContext) (Datum, bool) {
-	prevLTree, ok := d.LTree.Prev()
-	if !ok {
-		return nil, false
-	}
-	return NewDLTree(prevLTree), true
+	return nil, false
 }
 
 // Next implements the Datum interface.

pkg/util/ltree/ltree.go

@@ -131,27 +131,6 @@ func (lt T) Copy() T {
 	return T{path: copiedLabels}
 }
 
-// Prev returns the lexicographically previous LTree and a bool
-// indicating whether it exists.
-func (lt T) Prev() (T, bool) {
-	if lt.Len() == 0 {
-		return Empty, false
-	}
-
-	lastLabel := lt.path[lt.Len()-1]
-	if l := prevLabel(lastLabel); l != "" {
-		result := lt.Copy()
-		result.path[lt.Len()-1] = l
-		return result, true
-	}
-
-	if lt.Len() > 1 {
-		return T{path: lt.path[:lt.Len()-1]}, true
-	}
-
-	return Empty, true
-}
-
 // validateLabel checks if a label is valid and returns an error if it is not,
 // otherwise, it returns nil.
 // A label is valid if it:
@@ -173,43 +152,7 @@ func validateLabel(l string) error {
 	return nil
 }
 
-// prevLabel returns the lexicographically previous label or empty string if
-// none exists.
-func prevLabel(s string) string {
-	if len(s) == 0 {
-		return ""
-	}
-
-	lastChar := s[len(s)-1]
-	if prev := prevChar(lastChar); prev != 0 {
-		return s[:len(s)-1] + string(prev)
-	}
-
-	if len(s) > 1 {
-		return s[:len(s)-1]
-	}
-
-	return ""
-}
-
 // isValidChar returns true if the character is valid in an LTree label.
 func isValidChar(c byte) bool {
 	return (c >= '0' && c <= '9') || (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || (c == '_') || (c == '-')
 }
-
-var prevCharMap = map[byte]byte{
-	'-': 0,
-	'0': '-',
-	'A': '9',
-	'_': 'Z',
-	'a': '_',
-}
-
-// prevChar returns the previous valid character assuming a given valid
-// character, or 0 if none exists.
-func prevChar(c byte) byte {
-	if prev, ok := prevCharMap[c]; ok {
-		return prev
-	}
-	return c - 1
-}

pkg/util/ltree/ltree_test.go

@@ -152,110 +152,3 @@ func TestCompare(t *testing.T) {
 		}
 	}
 }
-
-func TestPrev(t *testing.T) {
-	tests := []struct {
-		input        string
-		expected     string
-		doesNotExist bool
-	}{
-		{
-			input:        "",
-			expected:     "",
-			doesNotExist: true,
-		},
-		{
-			input:    "b",
-			expected: "a",
-		},
-		{
-			input:    "a",
-			expected: "_",
-		},
-		{
-			input:    "_",
-			expected: "Z",
-		},
-		{
-			input:    "Z",
-			expected: "Y",
-		},
-		{
-			input:    "A",
-			expected: "9",
-		},
-		{
-			input:    "9",
-			expected: "8",
-		},
-		{
-			input:    "0",
-			expected: "-",
-		},
-		{
-			input:    "-",
-			expected: "",
-		},
-		{
-			input:    "ab",
-			expected: "aa",
-		},
-		{
-			input:    "a-",
-			expected: "a",
-		},
-		{
-			input:    "--",
-			expected: "-",
-		},
-		{
-			input:    "A.B",
-			expected: "A.A",
-		},
-		{
-			input:    "A.A",
-			expected: "A.9",
-		},
-		{
-			input:    "A.-",
-			expected: "A",
-		},
-		{
-			input:    "a.b.c",
-			expected: "a.b.b",
-		},
-		{
-			input:    "-.-.a",
-			expected: "-.-._",
-		},
-		{
-			input:    "-.-.-",
-			expected: "-.-",
-		},
-		{
-			input:    "abc.def",
-			expected: "abc.dee",
-		},
-		{
-			input:    "A",
-			expected: "9",
-		},
-	}
-
-	for _, tc := range tests {
-		input, err := ParseLTree(tc.input)
-		if err != nil {
-			t.Fatalf("unexpected error parsing input %q: %v", tc.input, err)
-		}
-
-		got, ok := input.Prev()
-
-		if ok && tc.doesNotExist {
-			t.Errorf("expected result to not exist, but got %q", got.String())
-		}
-
-		if ok && tc.expected != got.String() {
-			t.Errorf("expected %q, got %q", tc.expected, got.String())
-		}
-	}
-}