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feat: bat auto-detects language from stdin via first-line patterns

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When piped input has no filename hint, bat falls back to plain text. Many
common formats can be reliably identified by shebang or magic-string in the
first line (#!/bin/bash, <?xml, {"json: ...}, etc.). Adds a first-line
pattern matcher to assets.rs.

Fixes #3697
This commit is contained in:
Matt Van Horn
2026-05-16 13:51:00 -07:00
parent 4a38eab3ea
commit 530e83a455
2 changed files with 141 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files
tests/integration_tests.rs
+139
View File
@@ -2470,6 +2470,145 @@ fn no_first_line_fallback_when_mapping_to_invalid_syntax() {
.stderr(predicate::str::contains("unknown syntax: 'InvalidSyntax'"));
}
#[test]
fn stdin_detects_bash_from_first_line() {
let content = "#!/bin/bash\necho hi\n";
let detected_output = bat()
.arg("--color=always")
.arg("--style=plain")
.write_stdin(content)
.assert()
.success()
.get_output()
.stdout
.clone();
let explicit_output = bat()
.arg("--color=always")
.arg("--style=plain")
.arg("--language=bash")
.write_stdin(content)
.assert()
.success()
.get_output()
.stdout
.clone();
assert_eq!(
from_utf8(&detected_output).expect("output is valid utf-8"),
from_utf8(&explicit_output).expect("output is valid utf-8")
);
}
#[test]
fn stdin_detects_diff_from_first_line() {
let content = "diff --git a/x b/y\n--- a/x\n+++ b/y\n@@ -1 +1 @@\n-old\n+new\n";
let detected_output = bat()
.arg("--color=always")
.arg("--style=plain")
.write_stdin(content)
.assert()
.success()
.get_output()
.stdout
.clone();
let explicit_output = bat()
.arg("--color=always")
.arg("--style=plain")
.arg("--language=diff")
.write_stdin(content)
.assert()
.success()
.get_output()
.stdout
.clone();
assert_eq!(
from_utf8(&detected_output).expect("output is valid utf-8"),
from_utf8(&explicit_output).expect("output is valid utf-8")
);
}
#[test]
fn empty_stdin_does_not_detect_syntax() {
bat()
.arg("--color=always")
.arg("--style=plain")
.write_stdin("")
.assert()
.success()
.stdout("")
.stderr("");
}
#[test]
fn binary_stdin_does_not_detect_syntax_from_invalid_utf8_first_line() {
let content = b"#!/bin/bash\xff\necho hi\n";
let detected_output = bat()
.arg("--binary=as-text")
.arg("--color=always")
.arg("--style=plain")
.write_stdin(content.as_slice())
.assert()
.success()
.get_output()
.stdout
.clone();
let plain_text_output = bat()
.arg("--binary=as-text")
.arg("--color=always")
.arg("--style=plain")
.arg("--language=txt")
.write_stdin(content.as_slice())
.assert()
.success()
.get_output()
.stdout
.clone();
assert_eq!(
from_utf8(&detected_output).expect("output is valid utf-8"),
from_utf8(&plain_text_output).expect("output is valid utf-8")
);
}
#[test]
fn explicit_language_overrides_stdin_first_line_detection() {
let content = "diff --git a/x b/y\n--- a/x\n+++ b/y\n@@ -1 +1 @@\n-old\n+new\n";
let detected_output = bat()
.arg("--color=always")
.arg("--style=plain")
.write_stdin(content)
.assert()
.success()
.get_output()
.stdout
.clone();
let explicit_output = bat()
.arg("--color=always")
.arg("--style=plain")
.arg("--language=json")
.arg("-")
.write_stdin(content)
.assert()
.success()
.get_output()
.stdout
.clone();
assert_ne!(
from_utf8(&detected_output).expect("output is valid utf-8"),
from_utf8(&explicit_output).expect("output is valid utf-8")
);
}
#[test]
fn fallback_syntax_is_used_when_no_syntax_is_detected() {
let content = "# comment\nfoo=bar\n";