Match debug impl makes it look like matches are bigger than they really are

[HerrMuellerluedenscheid]

What version of regex are you using?

regex = "1.6.0"

This is the text against which I'm matching:

From 65ac1b403b1b2df05bbbe06c4795f9da24da4a07 Mon Sep 17 00:00:00 2001
From: xxx xxx <[email protected]>
Date: Sat, 3 Sep 2022 02:33:38 +0200
Subject: [PATCH 1/1] test patch

Signed-off-by: xxx xxx <[email protected]>
---
 README.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/README.md b/README.md
index e85faf1..698f024 100644
--- a/README.md
+++ b/README.md
@@ -1,3 +1,4 @@
+PATCHED
 Snitch - Intrusion Notification
 ===============================
 
-- 
2.36.1

This is the regex: From ((.|\n)*)\n-{3}\n

That should match until the three dash separator --- on the 7th line as it does here: https://regex101.com/r/9balQ3/1

This is how I call regex in my module:

static COMMIT_HEADER: &str = r"From ((.|\n)*)\n-{3}\n";
 
...
    let re = Regex::new(COMMIT_HEADER).unwrap();
    println!(" {:?}", re.find(std::str::from_utf8(&buff).unwrap()));

Unfortunately, regex matches the entire string down to the very list byte.

I guess I'm doing something wrong but its suprising that other tools match what I would expect.

Best regards

[HerrMuellerluedenscheid]

My bad! In case someone else runs into a similar confusion: the get from a capture returns the string including the start and stop byte where the expression matched.

[BurntSushi]

In the future, it is much more helpful to provide a running program. And since the regex crate is available in the playground, it's even nicer to use that. But here's a program that I believe captures what you said:

use regex::Regex;

static COMMIT_HEADER: &str = r"From ((.|\n)*)\n-{3}\n";

fn main() {
    let re = Regex::new(COMMIT_HEADER).unwrap();
    let haystack = "\
From 65ac1b403b1b2df05bbbe06c4795f9da24da4a07 Mon Sep 17 00:00:00 2001
From: xxx xxx <[email protected]>
Date: Sat, 3 Sep 2022 02:33:38 +0200
Subject: [PATCH 1/1] test patch

Signed-off-by: xxx xxx <[email protected]>
---
 README.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/README.md b/README.md
index e85faf1..698f024 100644
--- a/README.md
+++ b/README.md
@@ -1,3 +1,4 @@
+PATCHED
 Snitch - Intrusion Notification
 ===============================

--
2.36.1
";
    println!(" {:?}", re.find(haystack));
}

Playground link: https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=182138a3fb05ac34d7744c0096dca04e

And its output is:

Some(Match { text: "From 65ac1b403b1b2df05bbbe06c4795f9da24da4a07 Mon Sep 17 00:00:00 2001\nFrom: xxx xxx <[email protected]>\nDate: Sat, 3 Sep 2022 02:33:38 +0200\nSubject: [PATCH 1/1] test patch\n\nSigned-off-by: xxx xxx <[email protected]>\n---\n README.md | 1 +\n 1 file changed, 1 insertion(+)\n\ndiff --git a/README.md b/README.md\nindex e85faf1..698f024 100644\n--- a/README.md\n+++ b/README.md\n@@ -1,3 +1,4 @@\n+PATCHED\n Snitch - Intrusion Notification\n ===============================\n \n-- \n2.36.1\n", start: 0, end: 222 })

So I'm guessing the text field value here led you astray? The issue here is that the Debug impl for Match is not great (#514 is for improving it). But if we change the println! statement to

println!("{:?}", re.find(haystack).unwrap().as_str());

Then its output is:

"From 65ac1b403b1b2df05bbbe06c4795f9da24da4a07 Mon Sep 17 00:00:00 2001\nFrom: xxx xxx <[email protected]>\nDate: Sat, 3 Sep 2022 02:33:38 +0200\nSubject: [PATCH 1/1] test patch\n\nSigned-off-by: xxx xxx <[email protected]>\n---\n"

Which I believe lines up with your expectations.