Name the setting and value when a size does not parse (closes #429)

A size setting such as chunk_size: banana failed with "invalid size
format: strconv.ParseFloat: parsing "": invalid syntax", naming neither
the setting nor the value. The size decoder now quotes the value, and
Parse checks every size setting after ${...} references are filled in,
so the error reads chunk_size: "banana" is not a size; use a number of
bytes or a unit such as 10MB. This covers chunk_size, blob_size_limit
and s3.part_size, and config set.

Model: opus-5-5

internal/cli/config_test.go

@@ -252,7 +252,7 @@ func TestConfigSetKeepsFileThatWouldNotLoad(t *testing.T) {
 		{configWithoutRecipients, "snapshots.home.paths", "/srv",
 			"into []string"},
 		{configWithoutRecipients, "chunk_size", "fast",
-			"invalid size format"},
+			`chunk_size: "fast" is not a size`},
 		// Values of the right type that fail validation.
 		{configWithoutRecipients, "compression_level", "99",
 			"compression_level must be between 1 and 19"},

internal/config/config.go

@@ -287,7 +287,8 @@ func Load(path string) (*Config, error) {
 }
 
 // Parse reads YAML config data as Load does, without validating it. It
-// refuses a key that no setting has, applies default values for optional
+// refuses a key that no setting has and a size setting whose value is not a
+// size, naming the setting. It applies default values for optional
 // fields, fills in ${...} references using smartconfig, and expands ~ in
 // paths.
 func Parse(data []byte) (*Config, error) {
@@ -312,8 +313,9 @@ func Parse(data []byte) (*Config, error) {
 		return nil, fmt.Errorf("failed to load config file: %w", err)
 	}
 
-	// A ${...} reference can bring in keys that are not in the file.
+	// A ${...} reference can bring in keys that are not in the file, and
-	err = checkFilledKeys(sc.Data())
+	// is the value of a size setting only once it is filled in.
+	err = checkFilledConfig(sc.Data())
 	if err != nil {
 		return nil, err
 	}

internal/config/keys.go

@@ -129,10 +129,11 @@ func checkKeys(node *yaml.Node, typ reflect.Type, path string,
 	return nil
 }
 
-// checkFilledKeys is checkKeys for data, the config after smartconfig has
+// checkFilledConfig checks data, the config after smartconfig has filled in
-// filled in its ${...} references. A key that a reference brings in is not
+// its ${...} references: its keys with checkKeys, then its size settings
-// in the file, and the copy that Encode makes has no line numbers.
+// with checkSizes. A key that a reference brings in is not in the file, and
-func checkFilledKeys(data map[string]any) error {
+// the copy that Encode makes has no line numbers.
+func checkFilledConfig(data map[string]any) error {
 	var filled yaml.Node
 
 	err := filled.Encode(data)
@@ -140,8 +141,13 @@ func checkFilledKeys(data map[string]any) error {
 		return fmt.Errorf("failed to marshal config data: %w", err)
 	}
 
-	return checkKeys(&filled, reflect.TypeFor[Config](), "",
+	err = checkKeys(&filled, reflect.TypeFor[Config](), "",
 		map[*yaml.Node]bool{}, map[nodeAndType]bool{})
+	if err != nil {
+		return err
+	}
+
+	return checkSizes(&filled, nil)
 }
 
 // checkMappingKeys is checkKeys for a map.

internal/config/size.go

@@ -4,13 +4,20 @@ import (
 	"errors"
 	"fmt"
 	"math"
+	"reflect"
+	"slices"
+	"strconv"
+	"strings"
 
 	"github.com/dustin/go-humanize"
+	"gopkg.in/yaml.v3"
 )
 
 var (
 	errSizeType     = errors.New("size must be a number or string")
 	errSizeTooLarge = errors.New("size exceeds maximum supported value")
+	errNotASize     = errors.New(
+		"is not a size; use a number of bytes or a unit such as 10MB")
 )
 
 // Size represents a byte size that can be specified in configuration files.
@@ -40,17 +47,64 @@ func (s *Size) UnmarshalYAML(unmarshal func(any) error) error {
 		return errSizeType
 	}
 
-	// Parse the string using go-humanize
+	size, err := ParseSize(strVal)
-	bytes, err := humanize.ParseBytes(strVal)
 	if err != nil {
-		return fmt.Errorf("invalid size format: %w", err)
+		return err
 	}
 
-	if bytes > math.MaxInt64 {
+	*s = size
-		return fmt.Errorf("%w: %s", errSizeTooLarge, strVal)
+
+	return nil
+}
+
+// checkSizes returns an error naming the first size setting in node whose
+// value is not a size. node is the config, or the part of it at the dotted
+// keys, after smartconfig has filled in its ${...} references.
+func checkSizes(node *yaml.Node, keys []string) error {
+	typ, err := SettingType(keys)
+	if err != nil {
+		// Unknown keys are refused before this check, so this is the env
+		// section, which holds no settings.
+		return nil //nolint:nilerr // not an error here
 	}
 
-	*s = Size(bytes)
+	if typ == reflect.TypeFor[Size]() {
+		var size Size
+
+		err = node.Decode(&size)
+		if err != nil {
+			return fmt.Errorf("%s: %w", strings.Join(keys, "."), err)
+		}
+
+		return nil
+	}
+
+	switch node.Kind {
+	case yaml.DocumentNode:
+		for _, child := range node.Content {
+			err = checkSizes(child, keys)
+			if err != nil {
+				return err
+			}
+		}
+	case yaml.MappingNode:
+		for i := 0; i+1 < len(node.Content); i += 2 {
+			err = checkSizes(node.Content[i+1],
+				slices.Concat(keys, []string{node.Content[i].Value}))
+			if err != nil {
+				return err
+			}
+		}
+	case yaml.SequenceNode:
+		for i, child := range node.Content {
+			err = checkSizes(child, slices.Concat(keys, []string{strconv.Itoa(i)}))
+			if err != nil {
+				return err
+			}
+		}
+	case yaml.ScalarNode, yaml.AliasNode:
+		// A scalar holds no settings, and the filled config has no aliases.
+	}
 
 	return nil
 }
@@ -70,11 +124,12 @@ func (s Size) String() string {
 	return humanize.Bytes(uint64(s))
 }
 
-// ParseSize parses a size string into a Size value
+// ParseSize parses a size string, such as "10MB", into a Size value. An
+// error quotes s.
 func ParseSize(s string) (Size, error) {
 	bytes, err := humanize.ParseBytes(s)
 	if err != nil {
-		return 0, fmt.Errorf("invalid size format: %w", err)
+		return 0, fmt.Errorf("%q %w", s, errNotASize)
 	}
 
 	if bytes > math.MaxInt64 {

internal/config/size_test.go

@@ -0,0 +1,89 @@
+package config //nolint:testpackage // checks the unexported errNotASize
+
+import (
+	"errors"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+// TestParseRefusesValueThatIsNotASize checks that a size setting whose
+// value is not a size fails the parse with an error naming the setting and
+// quoting the value, also when a ${...} reference fills the value in.
+func TestParseRefusesValueThatIsNotASize(t *testing.T) {
+	t.Parallel()
+
+	sizePath := filepath.Join(t.TempDir(), "size")
+
+	err := os.WriteFile(sizePath, []byte("lots"), 0o600)
+	if err != nil {
+		t.Fatalf("write size: %v", err)
+	}
+
+	tests := []struct {
+		name string
+		yaml string
+		want string
+	}{
+		{"chunk_size", keysTestConfig + "chunk_size: banana\n",
+			`chunk_size: "banana" is not a size; ` +
+				"use a number of bytes or a unit such as 10MB"},
+		{"blob_size_limit", keysTestConfig + "blob_size_limit: 10XB\n",
+			`blob_size_limit: "10XB" is not a size; ` +
+				"use a number of bytes or a unit such as 10MB"},
+		{"s3.part_size", strings.Replace(keysTestConfig, "  region:",
+			"  part_size: big\n  region:", 1),
+			`s3.part_size: "big" is not a size; ` +
+				"use a number of bytes or a unit such as 10MB"},
+		{"from a reference",
+			keysTestConfig + "chunk_size: ${FILE:" + sizePath + "}\n",
+			`chunk_size: "lots" is not a size; ` +
+				"use a number of bytes or a unit such as 10MB"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			_, err := Parse([]byte(tt.yaml))
+			if !errors.Is(err, errNotASize) {
+				t.Fatalf("Parse() error = %v, want errNotASize", err)
+			}
+
+			if err.Error() != tt.want {
+				t.Errorf("Parse() error = %q, want %q", err.Error(), tt.want)
+			}
+		})
+	}
+}
+
+// TestParseAcceptsSizes checks that size settings given as a number of
+// bytes, as a unit, and through a ${...} reference still parse.
+func TestParseAcceptsSizes(t *testing.T) {
+	t.Parallel()
+
+	sizePath := filepath.Join(t.TempDir(), "size")
+
+	err := os.WriteFile(sizePath, []byte("20MB"), 0o600)
+	if err != nil {
+		t.Fatalf("write size: %v", err)
+	}
+
+	data := strings.Replace(keysTestConfig, "  region:",
+		"  part_size: 6000000\n  region:", 1) +
+		"chunk_size: ${FILE:" + sizePath + "}\n" +
+		"blob_size_limit: 1GB\n"
+
+	cfg, err := Parse([]byte(data))
+	if err != nil {
+		t.Fatalf("Parse() unexpected error: %v", err)
+	}
+
+	if cfg.ChunkSize != 20_000_000 || cfg.BlobSizeLimit != 1_000_000_000 ||
+		cfg.S3.PartSize != 6_000_000 {
+		t.Errorf("chunk_size, blob_size_limit, s3.part_size = %d, %d, %d, "+
+			"want 20000000, 1000000000, 6000000",
+			cfg.ChunkSize, cfg.BlobSizeLimit, cfg.S3.PartSize)
+	}
+}