tracing: add minimal format suitable for datadriven tests

I'd like to make the trace events emitted from deterministic multi-metric
allocator tests part of the expected test outputs.

I realized there wasn't a standardized deterministic and barebones output
format, so I added one.

Epic: none

Author: tbg

pkg/BUILD.bazel

@@ -835,6 +835,7 @@ ALL_TESTS = [
     "//pkg/util/tracing/goexectrace:goexectrace_test",
     "//pkg/util/tracing/grpcinterceptor:grpcinterceptor_test",
     "//pkg/util/tracing/service:service_test",
+    "//pkg/util/tracing/tracingpb:tracingpb_test",
     "//pkg/util/tracing:tracing_test",
     "//pkg/util/treeprinter:treeprinter_test",
     "//pkg/util/trigram:trigram_test",
@@ -2842,6 +2843,7 @@ GO_TARGETS = [
     "//pkg/util/tracing/service:service",
     "//pkg/util/tracing/service:service_test",
     "//pkg/util/tracing/tracingpb:tracingpb",
+    "//pkg/util/tracing/tracingpb:tracingpb_test",
     "//pkg/util/tracing/tracingservicepb:tracingservicepb",
     "//pkg/util/tracing/tracingui:tracingui",
     "//pkg/util/tracing/tracingutil:tracingutil",

pkg/util/tracing/tracingpb/BUILD.bazel

@@ -1,6 +1,6 @@
 load("@rules_proto//proto:defs.bzl", "proto_library")
 load("@io_bazel_rules_go//proto:def.bzl", "go_proto_library")
-load("@io_bazel_rules_go//go:def.bzl", "go_library")
+load("@io_bazel_rules_go//go:def.bzl", "go_library", "go_test")
 
 go_library(
     name = "tracingpb",
@@ -51,3 +51,20 @@ go_proto_library(
         "@com_github_gogo_protobuf//gogoproto",
     ],
 )
+
+go_test(
+    name = "tracingpb_test",
+    srcs = [
+        "condense_test.go",
+        "recording_test.go",
+    ],
+    data = glob(["testdata/**"]),
+    embed = [":tracingpb"],
+    deps = [
+        "//pkg/testutils/datapathutils",
+        "//pkg/testutils/echotest",
+        "//pkg/util/log",
+        "//pkg/util/tracing",
+        "@com_github_cockroachdb_redact//:redact",
+    ],
+)

pkg/util/tracing/tracingpb/condense_test.go

@@ -0,0 +1,79 @@
+// Copyright 2025 The Cockroach Authors.
+//
+// Use of this software is governed by the CockroachDB Software License
+// included in the /LICENSE file.
+
+package tracingpb
+
+import (
+	"testing"
+
+	"github.com/cockroachdb/redact"
+)
+
+func TestCondensePathLinePrefix(t *testing.T) {
+	for _, test := range []struct {
+		name     string
+		input    string
+		expected string
+	}{
+		{
+			name:     "no_directory",
+			input:    "foo.go:1234 message",
+			expected: "message",
+		},
+		{
+			name:     "full_path",
+			input:    "pkg/foo/bar.go:123 message",
+			expected: "message",
+		},
+		{
+			// Won't redact because there are redaction markers in the path.
+			// This doesn't happen in the real world but we want to make sure
+			// condensePathLinePrefix doesn't mess with redaction at all.
+			name:     "redaction_in_path",
+			input:    "pkg/‹foo›/bar.go:123 message",
+			expected: "pkg/‹foo›/bar.go:123 message",
+		},
+		{
+			// Redaction in message is expected and okay, since
+			// condensePathLinePrefix is written in a way to
+			// preserve that.
+			name:     "redaction_in_message",
+			input:    "pkg/foo/bar.go:123 ‹sensitive› message",
+			expected: "‹sensitive› message",
+		},
+		{
+			// Not expecting it in the real world since we only call
+			// condensePathLinePrefix in formatMinimal, but if we get formatFull, it
+			// also works.
+			name:     "full_format",
+			input:    "event: pkg/foo/bar.go:1234 ‹sensitive› message",
+			expected: "‹sensitive› message",
+		},
+		{
+			name:     "unredacted_trace",
+			input:    "‹pkg/foo/bar.go:1234 some message›",
+			expected: "‹some message›",
+		},
+		{
+			// Should never happen (there would be escaping). But either way, works
+			// just the same.
+			name:     "unredacted_trace_nested_unescaped",
+			input:    "‹pkg/foo/bar.go:1234 some ‹message››",
+			expected: "‹some ‹message››",
+		},
+		{
+			name:     "unredacted_trace_nested_escaped",
+			input:    "‹pkg/foo/bar.go:1234 " + string(redact.EscapeMarkers([]byte("some ‹message›"))) + "›",
+			expected: "‹some ?message?›", // NB: this is verbatim the escaped string inserted above
+		},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			got := string(condensePathLinePrefix(redact.RedactableString(test.input)))
+			if got != test.expected {
+				t.Errorf("expected %q, got %q", test.expected, got)
+			}
+		})
+	}
+}