Fix 1979: mib-bytes writes the bytes as a whole number for every size

A size of a million MiB or more reached the file in exponent form and was refused.

Builds: design 42 zfs-owns-zfs §3, A-24

internal/compose/resolution/config_lines.go

@@ -3,6 +3,7 @@ package resolution
 import (
 	"encoding/json"
 	"fmt"
+	"math"
 	"regexp"
 	"slices"
 	"strconv"
@@ -45,7 +46,7 @@ func configLinesInto(content string, layers []mcat.Layer, module string) (string
 				return token
 			}
 			if mib {
-				n, err := strconv.ParseUint(text, 10, 64)
+				n, err := mibWhole(text)
 				if err != nil || n > 1<<44 {
 					refused = fmt.Errorf("%s: the config value %q holds %q, and mib-bytes writes a whole number of MiB "+
 						"in bytes (design 42 §3)", module, key, text)
@@ -92,6 +93,19 @@ func configJSONInto(content string, layers []mcat.Layer, declared []string) (str
 	return configJSONRef.ReplaceAllLiteralString(content, object), nil
 }
 
+// mibWhole is a size in MiB as a whole number: digits, or a whole number a program wrote in exponent form (`1e+06`),
+// which is how a float of a million or more prints (design 42 §3).
+func mibWhole(text string) (uint64, error) {
+	if n, err := strconv.ParseUint(text, 10, 64); err == nil {
+		return n, nil
+	}
+	f, err := strconv.ParseFloat(text, 64)
+	if err != nil || f < 0 || f != math.Trunc(f) || f > 1<<44 {
+		return 0, fmt.Errorf("not a whole number of MiB")
+	}
+	return uint64(f), nil
+}
+
 // declaredConfig is the keys a module's manifest declares under `config`.
 func declaredConfig(m mcat.Manifest) []string {
 	keys := make([]string, 0, len(m.Settings))

internal/compose/resolution/setting_into_test.go

@@ -54,6 +54,14 @@ func TestAConfigValueReachesAResourceAndDecidesWhetherItIsDeclared(t *testing.T)
 			[]string{"${setting:domain}", "settings set mail", "set today: other"}},
 		{"config-lines: a list of two writes two lines in order", values(map[string]any{"k": []any{"a", "b"}}),
 			filled("h\n${config-lines:k:options zfs x=}\nt\n"), "h\noptions zfs x=a\noptions zfs x=b\nt\n", nil},
+		{"config-lines: mib-bytes writes a million MiB as a whole number", values(map[string]any{"k": float64(1000000)}),
+			filled("${config-lines:k:zfs_arc_max=:mib-bytes}\n"), "zfs_arc_max=1048576000000\n", nil},
+		{"config-lines: mib-bytes writes a million MiB given as text as a whole number", values(map[string]any{"k": "1000000"}),
+			filled("${config-lines:k:zfs_arc_max=:mib-bytes}\n"), "zfs_arc_max=1048576000000\n", nil},
+		{"config-lines: mib-bytes writes a size printed in exponent form as a whole number", values(map[string]any{"k": "1e+06"}),
+			filled("${config-lines:k:zfs_arc_max=:mib-bytes}\n"), "zfs_arc_max=1048576000000\n", nil},
+		{"config-lines: mib-bytes refuses a fraction", values(map[string]any{"k": "1.5"}),
+			filled("${config-lines:k:zfs_arc_max=:mib-bytes}\n"), "${config-lines:k:zfs_arc_max=:mib-bytes}\n", []string{"mib-bytes"}},
 		{"config-lines: an empty list writes nothing", values(map[string]any{"k": []any{}}),
 			filled("h\n${config-lines:k:p=}\nt\n"), "h\nt\n", nil},
 		{"config-lines: an unset value writes nothing", nil, filled("h\n${config-lines:k:p=}\nt\n"), "h\nt\n", nil},