Build modules: a failed command's reason says its error, not its last progress line (issue 1703)

buildah writes STEP lines on stdout and its error on stderr, so the last line of both hid every image build's cause.
mesh-build-image's reason is now stderr's last lines (600 bytes) with the exit status, and the journal gets both tails;
mesh-build-node keeps stderr's end and stdout's start apart; mesh-build-go's cause skips go build's '# package' line.

modules/mesh-build-node/cmd/mesh-build-node/build_test.go

@@ -267,3 +267,38 @@ func TestTheLaunchersAreTheSDKsRule(t *testing.T) {
 		t.Errorf("launchers %v, mesh-sdk's rule %v", got, want)
 	}
 }
+
+// issue 1703: a failed command's reason keeps stderr's end and stdout's start, each bounded, so a long stdout (npm's
+// progress) never pushes npm's error out, and tsc's first error on stdout stays in.
+func TestRanFailedKeepsTheError(t *testing.T) {
+	noise := strings.Repeat("npm progress line\n", 200)
+	cases := map[string]struct {
+		ran     forgekey.Ran
+		want    []string
+		wantNot []string
+	}{
+		"passed":           {forgekey.Ran{Stdout: "ok"}, nil, nil},
+		"npm, long stdout": {forgekey.Ran{Status: 1, Stdout: noise, Stderr: "npm ERR! early\n" + noise + "npm ERR! code E404\n"}, []string{"status 1", "npm ERR! code E404"}, []string{"npm ERR! early"}},
+		"tsc on stdout":    {forgekey.Ran{Status: 2, Stdout: "src/a.ts(1,7): error TS2322: wrong\n" + noise}, []string{"error TS2322"}, nil},
+		"never ran":        {forgekey.Ran{Err: "ENOENT"}, []string{"ENOENT"}, nil},
+	}
+	for name, c := range cases {
+		got := ranFailed(c.ran)
+		if c.want == nil && got != "" {
+			t.Errorf("%s: %q, want none", name, got)
+		}
+		for _, w := range c.want {
+			if !strings.Contains(got, w) {
+				t.Errorf("%s: %q lacks %q", name, got, w)
+			}
+		}
+		for _, w := range c.wantNot {
+			if strings.Contains(got, w) {
+				t.Errorf("%s: %q carries %q", name, got, w)
+			}
+		}
+		if len(got) > failedBytes+100 {
+			t.Errorf("%s: %d bytes, past its bound", name, len(got))
+		}
+	}
+}

modules/mesh-build-node/cmd/mesh-build-node/workspace.go

@@ -180,14 +180,28 @@ func (m *Module) runIn(ctx context.Context, root string, write bool, dir string,
 	return run(ctx, extra, "env", append([]string{"-C", dir, name}, args...)...)
 }
 
-// ranFailed says why a command did not pass, or "" when it did.
+// ranFailed says why a command did not pass, or "" when it did (issue 1703): its exit status, the end of what it wrote
+// on stderr (npm's error is its last lines) and the start of what it wrote on stdout (tsc writes its errors there,
+// first first), each bounded, so a long stdout never pushes stderr's error out of the reason.
 func ranFailed(r forgekey.Ran) string {
 	if r.Status == 0 && r.Err == "" {
 		return ""
 	}
-	out := strings.TrimSpace(r.Stdout + "\n" + r.Stderr)
-	if len(out) > 1500 {
-		out = out[:1500] + " ..."
+	why := fmt.Sprintf("status %d %s", r.Status, r.Err)
+	if e := strings.TrimSpace(r.Stderr); e != "" {
+		if len(e) > failedBytes/2 {
+			e = "... " + e[len(e)-failedBytes/2:]
+		}
+		why += ": stderr: " + e
 	}
-	return fmt.Sprintf("status %d %s: %s", r.Status, r.Err, out)
+	if o := strings.TrimSpace(r.Stdout); o != "" {
+		if len(o) > failedBytes/2 {
+			o = o[:failedBytes/2] + " ..."
+		}
+		why += ": stdout: " + o
+	}
+	return why
 }
+
+// failedBytes bounds what ranFailed carries of a command's output, stderr and stdout half each.
+const failedBytes = 1500