util/log/logconfig: allow format for stderr log sink

Previously in #113532 we fixed the stderr sink log format
to `crdb-v2-tty`. This was deemed to be a regression, as
the stderr sink could previously be set to any available
format. This commit reverts the restriction.

The following are still true after this commit:
- `format` in `file-defaults` is not propagated to
`format` of the stderr sink. To set `stderr` format,
one must explicitly define it in the `stderr` sink
section of the log config.
- `format-options` in `file-defaults` are only applied
to stderr if the format of the stderr sink and that in
file-defaults are compatible.

Epic: none
Fixes: #128665

Release note (ops change): Users may set the log format
for the stderr sink by setting the `format` field in the
logging config under the `stderr` sink section.

pkg/util/log/logconfig/config.go

@@ -30,9 +30,6 @@ import (
 const DefaultFileFormat = `crdb-v2`
 
 // DefaultStderrFormat is the entry format for stderr sinks.
-// NB: The format for stderr is always set to `crdb-v2-tty`,
-// and cannot be changed. We enforce this in the validation step.
-// See: https://www.cockroachlabs.com/docs/stable/configure-logs#output-to-stderr
 const DefaultStderrFormat = `crdb-v2-tty`
 
 // DefaultFluentFormat is the entry format for fluent sinks

pkg/util/log/logconfig/testdata/validate

@@ -254,7 +254,7 @@ capture-stray-errors:
   dir: /default-dir
   max-group-size: 100MiB
 
-# Check that file-defaults format options are transferred to stderr if using a crdb-v2 format.
+# Check that file-defaults format options are transferred to stderr if using the same format (crdb-v2).
 yaml
 file-defaults:
   format: crdb-v2
@@ -276,7 +276,38 @@ capture-stray-errors:
   dir: /default-dir
   max-group-size: 100MiB
 
-# Check that file-defaults format options are NOT transferred to stderr if NOT using a crdb-v2 format.
+# Check that file-defaults format options are transferred to stderr if stderr is using the same format (json).
+yaml
+file-defaults:
+  format: json
+  format-options: {datetime-format: rfc3339, datetime-timezone: America/New_York}
+sinks:
+  stderr:
+    format: json
+----
+sinks:
+  file-groups:
+    default:
+      channels: {INFO: all}
+      filter: INFO
+      format: json
+      format-options:
+        datetime-format: rfc3339
+        datetime-timezone: America/New_York
+  stderr:
+    filter: NONE
+    format: json
+    format-options:
+      datetime-format: rfc3339
+      datetime-timezone: America/New_York
+capture-stray-errors:
+  enable: true
+  dir: /default-dir
+  max-group-size: 100MiB
+
+# Check that file-defaults format options are NOT transferred to stderr if stderr is NOT using the same format
+# as file-defaults.
+# Note that here, we are using the default stderr format crdb-v2-tty.
 yaml
 file-defaults:
   format: json
@@ -323,7 +354,7 @@ capture-stray-errors:
   dir: /default-dir
   max-group-size: 100MiB
 
-# Check that stderr always uses crdb-v2-tty format, even if we try to set it to an invalid format
+# Check that stderr can accept formats other than crdb-v2-tty.
 yaml
 sinks:
   stderr:
@@ -336,6 +367,7 @@ sinks:
       filter: INFO
   stderr:
     filter: NONE
+    format: crdb-v1-tty
 capture-stray-errors:
   enable: true
   dir: /default-dir

pkg/util/log/logconfig/validate.go

@@ -177,17 +177,12 @@ func (c *Config) Validate(defaultLogDir *string) (resErr error) {
 		c.Sinks.Stderr.Criticality = &bt
 	}
 	c.Sinks.Stderr.Auditable = nil
-	// The format parameter for stderr is set to `crdb-v2-tty` and cannot be changed.
-	// See docs: https://www.cockroachlabs.com/docs/stable/configure-logs#output-to-stderr
-	if *c.Sinks.Stderr.Format != DefaultStderrFormat {
-		f := DefaultStderrFormat
-		c.Sinks.Stderr.Format = &f
-	}
+
 	// FormatOptions are format-specific. We should only copy them over to StdErr from
-	// FileDefaults if FileDefaults is also making use of a crdb-v2 format. Otherwise,
+	// FileDefaults if FileDefaults specifies the same format as the stderr sink. Otherwise,
 	// we are likely to error when trying to apply an unsupported format option.
 	if c.FileDefaults.CommonSinkConfig.Format != nil &&
-		!strings.Contains(*c.FileDefaults.CommonSinkConfig.Format, "v2") &&
+		!canShareFormatOptions(*c.FileDefaults.CommonSinkConfig.Format, *c.Sinks.Stderr.Format) &&
 		!stdErrFormatOptionsOriginallySet {
 		c.Sinks.Stderr.CommonSinkConfig.FormatOptions = map[string]string{}
 	}
@@ -538,3 +533,14 @@ func propagateDefaults(target, source interface{}) {
 		}
 	}
 }
+
+// canShareFormatOptions returns true if f1 and f2 can share format options.
+// See log.FormatParsers for full list of supported formats.
+// Examples:
+//
+//	canShareFormatOptions("json", "json") => true
+//	canShareFormatOptions("crdb-v2", "crdb-v2-tty") => true
+//	canShareFormatOptions("crdb-v2", "json") => false
+func canShareFormatOptions(f1, f2 string) bool {
+	return strings.HasPrefix(f1, f2) || strings.HasPrefix(f2, f1)
+}