printer: fix --vimgrep for multi-line mode

It turned out that --vimgrep wasn't quite getting the column of each
match correctly. Instead of printing column numbers relative to the
current line, it was printing column numbers as byte offsets relative to
where the match began. To fix this, we simply subtract the offset of the
line number from the beginning of the match. If the beginning of the
match came before the start of the current line, then there's really
nothing sensible we can do other than to use a column number of 1, which
we now document.

Interestingly, existing tests were checking that the previous behavior
was intended. My only defense is that I somehow tricked myself into
thinking it was a byte offset instead of a column number.

Kudos to @bfrg for calling this out in #1866:
https://github.com/BurntSushi/ripgrep/issues/1866#issuecomment-841635553

2 files changed, 19 insertions, 1 deletions

diff --git a/tests/multiline.rs b/tests/multiline.rs
index 67fa650d..eb9cb4d5 100644
--- a/tests/multiline.rs
+++ b/tests/multiline.rs
@@ -77,7 +77,7 @@ rgtest!(vimgrep, |dir: Dir, mut cmd: TestCommand| {
     let expected = "\
 sherlock:1:16:For the Doctor Watsons of this world, as opposed to the Sherlock
 sherlock:1:57:For the Doctor Watsons of this world, as opposed to the Sherlock
-sherlock:2:57:Holmeses, success in the province of detective work must always
+sherlock:2:1:Holmeses, success in the province of detective work must always
 sherlock:3:49:be, to a very large extent, the result of luck. Sherlock Holmes
 sherlock:5:12:but Doctor Watson has to have it taken out for him and dusted,
 ";
diff --git a/tests/regression.rs b/tests/regression.rs
index b34fb0ff..2935a43e 100644
--- a/tests/regression.rs
+++ b/tests/regression.rs
@@ -864,3 +864,21 @@ use B;
     ]);
     eqnice!("2\n", cmd.stdout());
 });
+
+rgtest!(r1866, |dir: Dir, mut cmd: TestCommand| {
+    dir.create("test", "foobar\nfoobar\nfoo quux");
+    cmd.args(&[
+        "--multiline",
+        "--vimgrep",
+        r"foobar\nfoobar\nfoo|quux",
+        "test",
+    ]);
+
+    let expected = "\
+test:1:1:foobar
+test:2:1:foobar
+test:3:1:foo quux
+test:3:5:foo quux
+";
+    eqnice!(expected, cmd.stdout());
+});