pkg/build: share extractRootCause with openbsd

* pkg/build: share extractRootCause with openbsd

This should get kernel build errors reported in syz-ci console.

* Add a test

* lint

1 files changed, 24 insertions, 0 deletions

diff --git a/pkg/build/build_test.go b/pkg/build/build_test.go
index 1698d3bd8..830c4f39c 100644
--- a/pkg/build/build_test.go
+++ b/pkg/build/build_test.go
@@ -4,6 +4,7 @@
 package build
 
 import (
+	"bytes"
 	"os/exec"
 	"strings"
 	"testing"
@@ -34,3 +35,26 @@ func TestCompilerIdentity(t *testing.T) {
 		})
 	}
 }
+
+func TestExtractRootCause(t *testing.T) {
+	for _, s := range []struct{ e, expect string }{
+		{`
+cc -g -Werror db_break.c
+sys/dev/kcov.c:93:6: error: use of undeclared identifier 'kcov_cold123'; did you mean 'kcov_cold'?
+        if (kcov_cold123)
+            ^~~~~~~~~~~~
+            kcov_cold
+sys/dev/kcov.c:65:5: note: 'kcov_cold' declared here
+int kcov_cold = 1;
+    ^
+1 error generated.
+`,
+			"sys/dev/kcov.c:93:6: error: use of undeclared identifier 'kcov_cold123'; did you mean 'kcov_cold'?",
+		},
+	} {
+		got := extractCauseInner([]byte(s.e))
+		if !bytes.Equal([]byte(s.expect), got) {
+			t.Errorf("Expected %s, got %s", s.expect, got)
+		}
+	}
+}