string difference not visible due to "elided lines" #311
Comments
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My stand-alone tests were done in Go playground. The actual test above lives in a PR for Kubernetes master, which currently uses go-cmp v0.5.9. |
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The workaround for this is to split strings into []string at line breaks. I'm not doing that in the PR because I like the output less, but it has the necessary code commented out, just in case that it is needed. |
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This does seem like a bug in the reporter heuristics in how it determines what context to show. Can you provide a simple reproduction that I can run that reproduces this? |
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I tried to come up with a simpler reproducer, but so far without luck. I'll keep trying... |
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Thanks for looking into it. I tried to perform a repro with just the snippet you gave and it seemed to work properly. I could only test with the string as it appears after the transformation. I wonder if the transformer is somehow messing with the Just as a sanity check, make sure you're using the latest version of |
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It's the combination of embedding inside a struct and using a transformer which triggers it. Here's a reproducer: package main
import (
"fmt"
"strings"
"github.com/google/go-cmp/cmp"
"github.com/google/go-cmp/cmp/cmpopts"
"github.com/onsi/ginkgo/v2/reporters"
)
func main() {
expected := strings.Repeat("hello\n", 50)
actual := expected + "world\n"
// Works.
// fmt.Println(cmp.Diff(expected, actual,
// cmpopts.AcyclicTransformer("simplify", func(in string) string {
// return in
// }),
// ))
expectedSuite := reporters.JUnitTestSuite{
TestCases: []reporters.JUnitTestCase{
{
Name: "[It] e2e works",
SystemErr: expected,
},
},
}
actualSuite := reporters.JUnitTestSuite{
TestCases: []reporters.JUnitTestCase{
{
Name: "[It] e2e works",
SystemErr: actual,
},
},
}
// Works.
// fmt.Println(cmp.Diff(expectedSuite, actualSuite))
fmt.Println(cmp.Diff(expectedSuite, actualSuite,
cmpopts.AcyclicTransformer("simplify", func(in string) string {
return in
}),
))
}Output: The number of lines is irrelevant, it also stops doing the diff for less lines. It just chose a high number to demonstrate that the output then doesn't show the actual difference anymore. |
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cmp is at 0.5.9, the latest. |
Sometimes I get output where the relevant difference between two strings is not shown because one or both get truncated with
elided lines. Example:In this example, I started with the expected string set to empty, copied as much of the actual string as possible, and then repeated. But because not all of it was shown, I am missing some lines. I was hoping to get a diff with the missing lines, but the heuristics apparently decided to just show both strings.
The simplify function does some string->string replacement to get rid of some line numbers and time stamps.
It's not entirely clear to me why this happens. I tried to reproduce it with exactly these strings and without a transformer, but then it worked as expected (showed a diff). I also tried with a transformer, with the same result.
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