add unified diff lib

pkg/plugin/processor/builtin/internal/diff/README.md

@@ -0,0 +1,16 @@
+# Diff
+
+This package contains code taken from https://github.com/golang/tools/tree/master/internal/diff
+on February 15th, 2024. We need the code to create a unified diff between two strings.
+
+The code is left as-is, except two changes:
+
+- The imports were changed to reference the Conduit module path. This was done
+  using the following command:
+
+  ```sh
+  find . -type f -exec sed -i '' 's/golang.org\/x\/tools\/internal/github.com\/conduitio\/conduit\/pkg\/plugin\/processor\/builtin\/internal/g' {} +
+  ```
+
+- The package `golang.org/x/tools/internal/testenv` was added into the `diff` package,
+  as that's the only place it's used. It also only includes the required functions.

pkg/plugin/processor/builtin/internal/diff/diff.go

@@ -0,0 +1,176 @@
+// Copyright 2019 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.
+
+// Package diff computes differences between text files or strings.
+package diff
+
+import (
+	"fmt"
+	"sort"
+	"strings"
+)
+
+// An Edit describes the replacement of a portion of a text file.
+type Edit struct {
+	Start, End int    // byte offsets of the region to replace
+	New        string // the replacement
+}
+
+func (e Edit) String() string {
+	return fmt.Sprintf("{Start:%d,End:%d,New:%q}", e.Start, e.End, e.New)
+}
+
+// Apply applies a sequence of edits to the src buffer and returns the
+// result. Edits are applied in order of start offset; edits with the
+// same start offset are applied in they order they were provided.
+//
+// Apply returns an error if any edit is out of bounds,
+// or if any pair of edits is overlapping.
+func Apply(src string, edits []Edit) (string, error) {
+	edits, size, err := validate(src, edits)
+	if err != nil {
+		return "", err
+	}
+
+	// Apply edits.
+	out := make([]byte, 0, size)
+	lastEnd := 0
+	for _, edit := range edits {
+		if lastEnd < edit.Start {
+			out = append(out, src[lastEnd:edit.Start]...)
+		}
+		out = append(out, edit.New...)
+		lastEnd = edit.End
+	}
+	out = append(out, src[lastEnd:]...)
+
+	if len(out) != size {
+		panic("wrong size")
+	}
+
+	return string(out), nil
+}
+
+// ApplyBytes is like Apply, but it accepts a byte slice.
+// The result is always a new array.
+func ApplyBytes(src []byte, edits []Edit) ([]byte, error) {
+	res, err := Apply(string(src), edits)
+	return []byte(res), err
+}
+
+// validate checks that edits are consistent with src,
+// and returns the size of the patched output.
+// It may return a different slice.
+func validate(src string, edits []Edit) ([]Edit, int, error) {
+	if !sort.IsSorted(editsSort(edits)) {
+		edits = append([]Edit(nil), edits...)
+		SortEdits(edits)
+	}
+
+	// Check validity of edits and compute final size.
+	size := len(src)
+	lastEnd := 0
+	for _, edit := range edits {
+		if !(0 <= edit.Start && edit.Start <= edit.End && edit.End <= len(src)) {
+			return nil, 0, fmt.Errorf("diff has out-of-bounds edits")
+		}
+		if edit.Start < lastEnd {
+			return nil, 0, fmt.Errorf("diff has overlapping edits")
+		}
+		size += len(edit.New) + edit.Start - edit.End
+		lastEnd = edit.End
+	}
+
+	return edits, size, nil
+}
+
+// SortEdits orders a slice of Edits by (start, end) offset.
+// This ordering puts insertions (end = start) before deletions
+// (end > start) at the same point, but uses a stable sort to preserve
+// the order of multiple insertions at the same point.
+// (Apply detects multiple deletions at the same point as an error.)
+func SortEdits(edits []Edit) {
+	sort.Stable(editsSort(edits))
+}
+
+type editsSort []Edit
+
+func (a editsSort) Len() int { return len(a) }
+func (a editsSort) Less(i, j int) bool {
+	if cmp := a[i].Start - a[j].Start; cmp != 0 {
+		return cmp < 0
+	}
+	return a[i].End < a[j].End
+}
+func (a editsSort) Swap(i, j int) { a[i], a[j] = a[j], a[i] }
+
+// lineEdits expands and merges a sequence of edits so that each
+// resulting edit replaces one or more complete lines.
+// See ApplyEdits for preconditions.
+func lineEdits(src string, edits []Edit) ([]Edit, error) {
+	edits, _, err := validate(src, edits)
+	if err != nil {
+		return nil, err
+	}
+
+	// Do all deletions begin and end at the start of a line,
+	// and all insertions end with a newline?
+	// (This is merely a fast path.)
+	for _, edit := range edits {
+		if edit.Start >= len(src) || // insertion at EOF
+			edit.Start > 0 && src[edit.Start-1] != '\n' || // not at line start
+			edit.End > 0 && src[edit.End-1] != '\n' || // not at line start
+			edit.New != "" && edit.New[len(edit.New)-1] != '\n' { // partial insert
+			goto expand // slow path
+		}
+	}
+	return edits, nil // aligned
+
+expand:
+	if len(edits) == 0 {
+		return edits, nil // no edits (unreachable due to fast path)
+	}
+	expanded := make([]Edit, 0, len(edits)) // a guess
+	prev := edits[0]
+	// TODO(adonovan): opt: start from the first misaligned edit.
+	// TODO(adonovan): opt: avoid quadratic cost of string += string.
+	for _, edit := range edits[1:] {
+		between := src[prev.End:edit.Start]
+		if !strings.Contains(between, "\n") {
+			// overlapping lines: combine with previous edit.
+			prev.New += between + edit.New
+			prev.End = edit.End
+		} else {
+			// non-overlapping lines: flush previous edit.
+			expanded = append(expanded, expandEdit(prev, src))
+			prev = edit
+		}
+	}
+	return append(expanded, expandEdit(prev, src)), nil // flush final edit
+}
+
+// expandEdit returns edit expanded to complete whole lines.
+func expandEdit(edit Edit, src string) Edit {
+	// Expand start left to start of line.
+	// (delta is the zero-based column number of start.)
+	start := edit.Start
+	if delta := start - 1 - strings.LastIndex(src[:start], "\n"); delta > 0 {
+		edit.Start -= delta
+		edit.New = src[start-delta:start] + edit.New
+	}
+
+	// Expand end right to end of line.
+	end := edit.End
+	if end > 0 && src[end-1] != '\n' ||
+		edit.New != "" && edit.New[len(edit.New)-1] != '\n' {
+		if nl := strings.IndexByte(src[end:], '\n'); nl < 0 {
+			edit.End = len(src) // extend to EOF
+		} else {
+			edit.End = end + nl + 1 // extend beyond \n
+		}
+	}
+	edit.New += src[end:edit.End]
+
+	return edit
+}