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35ad0448c9
See https://github.com/siderolabs/omni/pull/2311 for the rationale. Signed-off-by: Andrey Smirnov <andrey.smirnov@siderolabs.com>
78 lines
2.3 KiB
Go
78 lines
2.3 KiB
Go
// This Source Code Form is subject to the terms of the Mozilla Public
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// License, v. 2.0. If a copy of the MPL was not distributed with this
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// file, You can obtain one at http://mozilla.org/MPL/2.0/.
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// Package textdiff provides a way to compare two text blobs.
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package textdiff
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import (
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"fmt"
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"strings"
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"github.com/neticdk/go-stdlib/diff/myers"
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)
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// MaxLines is the maximum number of lines that the diff function will process before giving up and returning a message instead.
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const MaxLines = 75_000
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// Diff is a function that computes unified diff between two strings.
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//
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// The diff is limited to MaxLines lines, and if the diff is larger than that, a message is returned instead of the actual diff.
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// This is to prevent the function from consuming too much memory or CPU time when comparing large text blobs.
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func Diff(a, b string) (string, error) {
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if a == b {
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return "", nil
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}
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prevLines := strings.Count(a, "\n")
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newLines := strings.Count(b, "\n")
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if prevLines+newLines > MaxLines {
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return fmt.Sprintf("@@ -%d,%d +%d,%d @@ diff too large to display\n", 1, prevLines, 1, newLines), nil
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}
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differ := myers.NewCustomDiffer(
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myers.WithUnifiedFormatter(),
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myers.WithLinearSpace(true),
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// Disable the library's standard-Myers and LCS fallback paths:
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// - Standard Myers (< smallInputThreshold) is O((N+M)²) when inputs are asymmetric.
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// - LCS (> largeInputThreshold) is O(N*M) for the DP table.
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// By setting these to 0 and MaxLines respectively, only Hirschberg's
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// O(N+M) linear-space algorithm runs. Our MaxLines guard above ensures
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// inputs never exceed largeInputThreshold.
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myers.WithSmallInputThreshold(0),
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myers.WithLargeInputThreshold(MaxLines),
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)
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return differ.Diff(a, b)
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}
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// DiffWithCustomPaths is almost same as Diff, but allows to specify custom paths for the diff header.
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func DiffWithCustomPaths(a, b, aPath, bPath string) (string, error) {
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diff, err := Diff(a, b)
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if err != nil {
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return "", err
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}
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if diff == "" {
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return "", nil
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}
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// patch the diff header to include the manifest path
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diff, ok := strings.CutPrefix(diff, "--- a\n+++ b\n")
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if !ok {
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return "", fmt.Errorf("unexpected diff format")
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}
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var sb strings.Builder
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sb.WriteString("--- ")
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sb.WriteString(aPath)
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sb.WriteString("\n+++ ")
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sb.WriteString(bPath)
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sb.WriteString("\n")
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sb.WriteString(diff)
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return sb.String(), nil
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}
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