acc: Shrink the regression report comment

.github/workflows/regression-report.yml

@@ -91,11 +91,21 @@ jobs:
             const runUrl = `${context.serverUrl}/${owner}/${repo}/actions/runs/${context.runId}`;
             const commitUrl = `${context.serverUrl}/${owner}/${repo}/commit/${sha}`;
 
-            // Comments are limited to 65536 characters; the artifact holds the full report.
+            // Comments are limited to 65536 characters; the artifact holds the full report. The table
+            // comes first, then one <details> block per failure: drop whole blocks that do not fit,
+            // as cutting one in the middle would leave its markup open.
             const MAX_REPORT = 60000;
             let report = fs.readFileSync(path, 'utf8');
             if (report.length > MAX_REPORT) {
-              report = report.slice(0, MAX_REPORT) + `\n\n_Report truncated, see the full report in the [run](${runUrl})._\n`;
+              const [head, ...blocks] = report.split('<details>\n');
+              let kept = head;
+              let shown = 0;
+              for (const block of blocks) {
+                if (kept.length + block.length > MAX_REPORT) break;
+                kept += '<details>\n' + block;
+                shown++;
+              }
+              report = kept + `_${blocks.length - shown} more failure details omitted, see the full report in the [run](${runUrl})._\n`;
             }
 
             const body = `${MARKER}\nCommit: [\`${sha.slice(0, 9)}\`](${commitUrl}) | [Workflow run](${runUrl})\n\n${report}`;

acceptance/regression_test.go

@@ -99,6 +99,9 @@ var (
 
 	// "    --- FAIL: TestAccept/foo (0.10s)"
 	resultLineRE = regexp.MustCompile(`^\s*--- (PASS|FAIL|SKIP): (\S+) `)
+
+	// The temp dir of a test, e.g. "/tmp/TestAcceptfoo123456"; the random suffix differs on every run.
+	tmpDirRE = regexp.MustCompile(`/TestAccept[^/\s]*`)
 )
 
 // parseTestOutput parses the output of a test binary run with -test.v into results by test name.
@@ -266,10 +269,19 @@ func renderDetails(b *strings.Builder, test string, columns []regrColumn) {
 		marks[i] = c.Title + " " + statusMark(c.status(test))
 	}
 	fmt.Fprintf(b, "<details>\n<summary>%s: %s</summary>\n\n", test, strings.Join(marks, " | "))
+	// A new test commonly fails the same way on main and on the release, which would print the
+	// same long diff twice.
+	firstWith := map[string]string{}
 	for _, c := range failed {
-		output := truncateLines(strings.Join(c.Results[test].Output, "\n"), regrDetailLines)
+		output := strings.TrimSpace(strings.Join(c.Results[test].Output, "\n"))
+		key := tmpDirRE.ReplaceAllString(output, "/TestAccept")
+		if first, ok := firstWith[key]; ok {
+			fmt.Fprintf(b, "**%s:** same output as %s\n\n", c.Title, first)
+			continue
+		}
+		firstWith[key] = c.Title
 		// The longer fence keeps backticks in the output from ending the block.
-		fmt.Fprintf(b, "**%s:**\n````\n%s\n````\n\n", c.Title, strings.TrimSpace(output))
+		fmt.Fprintf(b, "**%s:**\n````\n%s\n````\n\n", c.Title, truncateLines(output, regrDetailLines))
 	}
 	b.WriteString("</details>\n\n")
 }

acceptance/regression_unit_test.go

@@ -1,6 +1,7 @@
 package acceptance_test
 
 import (
+	"strings"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -66,3 +67,19 @@ func TestRenderRegressionReport(t *testing.T) {
 	assert.Contains(t, report, "**main (abc):**\n````\nmain failure\n````")
 	assert.Contains(t, report, "failing=1")
 }
+
+func TestRenderRegressionReportDedupesIdenticalFailures(t *testing.T) {
+	failure := func(tmp string) *testResult {
+		return &testResult{Status: statusFail, Output: []string{"Messages: output.txt vs /tmp/TestAcceptfoo" + tmp + "/002/output.txt", "diff"}}
+	}
+	test := "TestAccept/bundle/a"
+	columns := []regrColumn{
+		{Title: "branch", Results: map[string]*testResult{test: {Status: statusPass}}},
+		{Title: "main (abc)", Category: catRegression, Results: map[string]*testResult{test: failure("111")}},
+		{Title: "latest (v1)", Category: catUnreleased, Results: map[string]*testResult{test: failure("222")}},
+	}
+
+	report := renderRegressionReport("Selected 1", columns)
+	assert.Equal(t, 1, strings.Count(report, "\ndiff\n"))
+	assert.Contains(t, report, "**latest (v1):** same output as main (abc)")
+}