refactor: Changed Render_Error from Union to struct.

Also renamed it to `Error`.

mustache/diagnostic.odin

@@ -307,26 +307,17 @@ write_gutter :: proc(sb: ^strings.Builder, width: int, faint: string, reset: str
 	strings.write_byte(sb, '\n')
 }
 
-// format_render_error dispatches on Render_Error variant and produces a
+// format_render_error produces a diagnostic for an Error value using the
-// diagnostic for it. Returns "" for nil errors.
+// template's path and source for context. Returns "" for nil errors.
-format_render_error :: proc(err: Render_Error, tmpl: Template, colorize: bool = false) -> string {
+format_render_error :: proc(err: Error, tmpl: Template, colorize: bool = false) -> string {
 	if err == nil {
 		return ""
 	}
-	switch e in err {
-	case Syntax_Error:
 	path := tmpl.path
 	if path == "" {
 		path = "<input>"
 	}
-		return format_error(path, tmpl.source, e.pos, e.msg, colorize = colorize)
+	b := body(err)
-	case Data_Error:
+	return format_error(path, tmpl.source, b.pos, b.msg, colorize = colorize)
-		path := tmpl.path
-		if path == "" {
-			path = "<input>"
-		}
-		return format_error(path, tmpl.source, e.pos, e.msg, colorize = colorize)
-	}
-	return ""
 }
 

mustache/diagnostic_test.odin

@@ -425,13 +425,11 @@ test_format_render_error_dispatch :: proc(t: ^testing.T) {
 		return
 	}
 
-	#partial switch e in parse_err {
+	b := body(parse_err)
-	case Syntax_Error:
+	out := format_error("test.html", src, b.pos, b.msg, colorize = false)
-		out := format_error("test.html", src, e.pos, e.msg, colorize = false)
 	testing.expect(t, strings.contains(out, "unclosed section"), out)
 	testing.expect(t, strings.contains(out, "test.html:"), out)
 }
-}
 
 @(test)
 test_diagnostic_for_pipe_error :: proc(t: ^testing.T) {
@@ -469,20 +467,18 @@ test_parse_error_expected_got_keeps_double_braces :: proc(t: ^testing.T) {
 	if err == nil {
 		return
 	}
-	#partial switch e in err {
+	b := body(err)
-	case Syntax_Error:
 	testing.expect(
 		t,
-			strings.contains(e.msg, "{{/content}}"),
+		strings.contains(b.msg, "{{/content}}"),
-			fmt.tprintf("msg should contain literal {{/content}}, got %q", e.msg),
+		fmt.tprintf("msg should contain literal {{/content}}, got %q", b.msg),
 	)
 	testing.expect(
 		t,
-			strings.contains(e.msg, "{{/cotent}}"),
+		strings.contains(b.msg, "{{/cotent}}"),
-			fmt.tprintf("msg should contain literal {{/cotent}}, got %q", e.msg),
+		fmt.tprintf("msg should contain literal {{/cotent}}, got %q", b.msg),
 	)
 }
-}
 
 @(test)
 test_parse_error_unclosed_section_keeps_double_braces :: proc(t: ^testing.T) {
@@ -492,15 +488,13 @@ test_parse_error_unclosed_section_keeps_double_braces :: proc(t: ^testing.T) {
 	if err == nil {
 		return
 	}
-	#partial switch e in err {
+	b := body(err)
-	case Syntax_Error:
 	testing.expect(
 		t,
-			strings.contains(e.msg, "{{#content}}"),
+		strings.contains(b.msg, "{{#content}}"),
-			fmt.tprintf("msg should contain literal {{#content}}, got %q", e.msg),
+		fmt.tprintf("msg should contain literal {{#content}}, got %q", b.msg),
 	)
 }
-}
 
 @(test)
 test_parse_error_unexpected_close_keeps_double_braces :: proc(t: ^testing.T) {
@@ -510,15 +504,13 @@ test_parse_error_unexpected_close_keeps_double_braces :: proc(t: ^testing.T) {
 	if err == nil {
 		return
 	}
-	#partial switch e in err {
+	b := body(err)
-	case Syntax_Error:
 	testing.expect(
 		t,
-			strings.contains(e.msg, "{{/content}}"),
+		strings.contains(b.msg, "{{/content}}"),
-			fmt.tprintf("msg should contain literal {{/content}}, got %q", e.msg),
+		fmt.tprintf("msg should contain literal {{/content}}, got %q", b.msg),
 	)
 }
-}
 
 @(test)
 test_parse_error_pipe_in_close_tag_keeps_double_braces :: proc(t: ^testing.T) {
@@ -528,15 +520,13 @@ test_parse_error_pipe_in_close_tag_keeps_double_braces :: proc(t: ^testing.T) {
 	if err == nil {
 		return
 	}
-	#partial switch e in err {
+	b := body(err)
-	case Syntax_Error:
 	testing.expect(
 		t,
-			strings.contains(e.msg, "{{/"),
+		strings.contains(b.msg, "{{/"),
-			fmt.tprintf("msg should contain literal '{{/', got %q", e.msg),
+		fmt.tprintf("msg should contain literal '{{/', got %q", b.msg),
 	)
 }
-}
 
 @(test)
 test_parse_error_pipe_parse_in_section_keeps_double_braces :: proc(t: ^testing.T) {
@@ -546,15 +536,13 @@ test_parse_error_pipe_parse_in_section_keeps_double_braces :: proc(t: ^testing.T
 	if err == nil {
 		return
 	}
-	#partial switch e in err {
+	b := body(err)
-	case Syntax_Error:
 	testing.expect(
 		t,
-			strings.contains(e.msg, "{{#"),
+		strings.contains(b.msg, "{{#"),
-			fmt.tprintf("msg should contain literal '{{#', got %q", e.msg),
+		fmt.tprintf("msg should contain literal '{{#', got %q", b.msg),
 	)
 }
-}
 
 @(test)
 test_parse_error_pipe_parse_in_inverted_keeps_double_braces :: proc(t: ^testing.T) {
@@ -564,13 +552,11 @@ test_parse_error_pipe_parse_in_inverted_keeps_double_braces :: proc(t: ^testing.
 	if err == nil {
 		return
 	}
-	#partial switch e in err {
+	b := body(err)
-	case Syntax_Error:
 	testing.expect(
 		t,
-			strings.contains(e.msg, "{{^"),
+		strings.contains(b.msg, "{{^"),
-			fmt.tprintf("msg should contain literal '{{^', got %q", e.msg),
+		fmt.tprintf("msg should contain literal '{{^', got %q", b.msg),
 	)
 }
-}
 

mustache/mustache.odin

@@ -8,20 +8,27 @@ import "core:strings"
 // Error types
 // ---------------------------------------------------------------------------
 
-// TODO: I don't think this is the best way to do our errors.
+Error_Kind :: enum {
-Syntax_Error :: struct {
+	Syntax, // parse-time: malformed template
-	msg: string,
+	Data,   // render-time: template fine, data wrong (e.g. filter misuse)
-	pos: int,
 }
 
-Data_Error :: struct {
+Error_Body :: struct {
 	msg:  string,
 	pos:  int,
+	kind: Error_Kind,
 }
 
-Render_Error :: union {
+// Error is nil when no error occurred.
-	Syntax_Error,
+Error :: union { Error_Body }
-	Data_Error,
+
+// body unwraps the Error_Body from a non-nil Error.
+// Precondition: err != nil.
+body :: proc(err: Error) -> Error_Body {
+	switch e in err {
+	case Error_Body: return e
+	case: return {}
+	}
 }
 
 // ---------------------------------------------------------------------------
@@ -101,7 +108,7 @@ parse :: proc(
 	tokens_allocator := context.temp_allocator,
 ) -> (
 	tmpl: Template,
-	err: Render_Error,
+	err: Error,
 ) {
 	tokens, terr := tokenize(source, tokens_allocator)
 	if terr != nil {
@@ -126,7 +133,7 @@ render :: proc(
 	allocator := context.allocator,
 ) -> (
 	result: string,
-	err: Render_Error,
+	err: Error,
 ) {
 	builder: strings.Builder
 	strings.builder_init(&builder, allocator)
@@ -158,7 +165,7 @@ parse_tokens :: proc(
 	allocator := context.allocator,
 ) -> (
 	nodes: [dynamic]Node,
-	err: Render_Error,
+	err: Error,
 ) {
 	nodes = make([dynamic]Node, 0, len(tokens), allocator)
 	pos := 0
@@ -174,7 +181,7 @@ parse_section :: proc(
 	source: string,
 	allocator := context.allocator,
 	open_pos: int = 0,
-) -> Render_Error {
+) -> Error {
 	for pos^ < len(tokens) {
 		tok := tokens[pos^]
 
@@ -188,9 +195,10 @@ parse_section :: proc(
 			append(nodes, Node{kind = .Variable, first_child = -1})
 			pipe_key, perr := parse_pipeline(tok.value, &nodes[idx].filters, tok.pos)
 			if perr != nil {
-				return Syntax_Error {
+				return Error_Body {
 					msg = fmt.tprintf("pipe parse error in '{{{{%s}}}}': %v", tok.value, perr),
 					pos = tok.pos,
+					kind = .Syntax,
 				}
 			}
 			nodes[idx].key = pipe_key
@@ -201,9 +209,10 @@ parse_section :: proc(
 			append(nodes, Node{kind = .Unescaped, first_child = -1})
 			pipe_key, perr := parse_pipeline(tok.value, &nodes[idx].filters, tok.pos)
 			if perr != nil {
-				return Syntax_Error {
+				return Error_Body {
 					msg = fmt.tprintf("pipe parse error in '{{{{&%s}}}}': %v", tok.value, perr),
 					pos = tok.pos,
+					kind = .Syntax,
 				}
 			}
 			nodes[idx].key = pipe_key
@@ -220,9 +229,10 @@ parse_section :: proc(
 			append(nodes, Node{kind = .Section, first_child = -1, pos = tok.pos})
 			pipe_key, perr := parse_pipeline(tok.value, &nodes[idx].filters, tok.pos)
 			if perr != nil {
-				return Syntax_Error {
+				return Error_Body {
 					msg = fmt.tprintf("pipe parse error in '{{{{#%s}}}}': %v", tok.value, perr),
 					pos = tok.pos,
+					kind = .Syntax,
 				}
 			}
 			nodes[idx].key = pipe_key
@@ -241,9 +251,10 @@ parse_section :: proc(
 			append(nodes, Node{kind = .Inverted, first_child = -1, pos = tok.pos})
 			pipe_key, perr := parse_pipeline(tok.value, &nodes[idx].filters, tok.pos)
 			if perr != nil {
-				return Syntax_Error {
+				return Error_Body {
 					msg = fmt.tprintf("pipe parse error in '{{{{^%s}}}}': %v", tok.value, perr),
 					pos = tok.pos,
+					kind = .Syntax,
 				}
 			}
 			nodes[idx].key = pipe_key
@@ -256,12 +267,13 @@ parse_section :: proc(
 
 		case .Section_Close:
 			if strings.contains(tok.value, "|") {
-				return Syntax_Error {
+			return Error_Body {
 				msg = fmt.tprintf(
 					"pipe expression not allowed in close tag '{{{{/%s}}}}' — use the bare key",
 					tok.value,
 				),
 				pos = tok.pos,
+				kind = .Syntax,
 			}
 			}
 			if end_tag != "" && tok.value == end_tag {
@@ -269,14 +281,16 @@ parse_section :: proc(
 				return nil
 			}
 			if end_tag == "" {
-				return Syntax_Error {
+				return Error_Body {
 					msg = fmt.tprintf("unexpected {{{{/%s}}}}", tok.value),
 					pos = tok.pos,
+					kind = .Syntax,
 				}
 			}
-			return Syntax_Error {
+			return Error_Body {
 				msg = fmt.tprintf("expected {{{{/%s}}}}, got {{{{/%s}}}}", end_tag, tok.value),
 				pos = tok.pos,
+				kind = .Syntax,
 			}
 
 		case .Partial:
@@ -330,9 +344,10 @@ parse_section :: proc(
 	}
 
 	if end_tag != "" {
-		return Syntax_Error {
+		return Error_Body {
 			msg = fmt.tprintf("unclosed section '{{{{#%s}}}}'", end_tag),
 			pos = open_pos,
+			kind = .Syntax,
 		}
 	}
 	return nil
@@ -495,7 +510,7 @@ render_template :: proc(
 	b: ^strings.Builder,
 	blocks: map[string]Block_Override,
 	indent: string,
-) -> Render_Error {
+) -> Error {
 	if len(indent) > 0 && len(pt.source) > 0 {
 		// Per Mustache spec: the partial's source is indented before rendering,
 		// not its output. This is necessary so that data-injected newlines
@@ -525,7 +540,7 @@ render_nodes :: proc(
 	partials: map[string]Template,
 	b: ^strings.Builder,
 	blocks: map[string]Block_Override = nil,
-) -> Render_Error {
+) -> Error {
 	i := 0
 	for i < len(nodes) {
 		node := nodes[i]

mustache/pipes.odin

@@ -30,7 +30,7 @@ parse_pipeline :: proc(
 	pos: int,
 ) -> (
 	key: string,
-	err: Render_Error,
+	err: Error,
 ) {
 	if !strings.contains(content, "|") {
 		key = strings.trim_space(content)
@@ -41,19 +41,20 @@ parse_pipeline :: proc(
 
 	filter_count := len(segments) - 1
 	if filter_count > MAX_PIPES {
-		return "", Syntax_Error {
+		return "", Error_Body {
 			msg = fmt.tprintf(
 				"pipe expression has %d filters, max is %d",
 				filter_count,
 				MAX_PIPES,
 			),
 			pos = pos,
+			kind = .Syntax,
 		}
 	}
 
 	key = strings.trim_space(segments[0])
 	if len(key) == 0 {
-		return "", Syntax_Error{msg = "pipe expression missing key", pos = pos}
+		return "", Error_Body{msg = "pipe expression missing key", pos = pos, kind = .Syntax}
 	}
 
 	if filter_count == 0 {
@@ -63,17 +64,17 @@ parse_pipeline :: proc(
 	for i in 0 ..< filter_count {
 		seg := strings.trim_space(segments[i + 1])
 		if len(seg) == 0 {
-			return "", Syntax_Error{msg = "empty filter", pos = pos}
+			return "", Error_Body{msg = "empty filter", pos = pos, kind = .Syntax}
 		}
 
 		tokens := strings.fields(seg)
 		if len(tokens) == 0 {
-			return "", Syntax_Error{msg = "filter missing op name", pos = pos}
+			return "", Error_Body{msg = "filter missing op name", pos = pos, kind = .Syntax}
 		}
 
 		arg_count := len(tokens) - 1
 		if arg_count > MAX_PIPE_ARGS {
-			return "", Syntax_Error {
+			return "", Error_Body {
 				msg = fmt.tprintf(
 					"filter '%s' has %d args, max is %d",
 					tokens[0],
@@ -81,6 +82,7 @@ parse_pipeline :: proc(
 					MAX_PIPE_ARGS,
 				),
 				pos = pos,
+				kind = .Syntax,
 			}
 		}
 
@@ -97,7 +99,7 @@ parse_pipeline :: proc(
 	return key, nil
 }
 
-apply_pipeline :: proc(value: any, filters: []Pipe_Filter, pos: int) -> (any, Render_Error) {
+apply_pipeline :: proc(value: any, filters: []Pipe_Filter, pos: int) -> (any, Error) {
 	current := value
 	for &filter in filters {
 		result, err := apply_filter(current, &filter, pos)
@@ -109,28 +111,33 @@ apply_pipeline :: proc(value: any, filters: []Pipe_Filter, pos: int) -> (any, Re
 	return current, nil
 }
 
-apply_filter :: proc(value: any, filter: ^Pipe_Filter, pos: int) -> (any, Render_Error) {
+apply_filter :: proc(value: any, filter: ^Pipe_Filter, pos: int) -> (any, Error) {
 	switch filter.op {
 	case "group_by":
 		return apply_group_by(value, filter.args[:], pos)
 	case "format":
 		str, ok := reflect.as_string(value)
 		if !ok {
-			return value, Data_Error{msg = "format may only be used on dates", pos = pos}
+			return value, Error_Body{
+				msg = "format may only be used on dates",
+				pos = pos,
+				kind = .Data,
+			}
 		} else {
 			return apply_format(str, filter.args[:], pos)
 		}
 	case:
-		return nil, Data_Error{
+		return nil, Error_Body{
 			msg = fmt.tprintf("unknown pipe op '%s'", filter.op),
 			pos = pos,
+			kind = .Data,
 		}
 	}
 }
 
 // apply_format formats an ISO 8601 date string as a display string
 // (e.g. "2026-03-15T08:49:54-04:00" → "15 Mar 2026"). Invalid input
-// (empty, too-short, or unparseable) returns a `Data_Error`. Templates
+// (empty, too-short, or unparseable) returns a Data-kind `Error`. Templates
 // that need to skip dateless pages should gate with a section:
 //   {{#date}}<time datetime="{{.}}">{{. | format}}</time>{{/date}}
 // The section's truthiness check catches empty before the filter runs.
@@ -144,9 +151,13 @@ apply_filter :: proc(value: any, filter: ^Pipe_Filter, pos: int) -> (any, Render
 //   2023-10-15T13:18:50Z
 //   2023-10-15T13:18:50
 //   2023-10-15
-apply_format :: proc(iso: string, args: []string, pos: int) -> (result: any, err: Render_Error) {
+apply_format :: proc(iso: string, args: []string, pos: int) -> (result: any, err: Error) {
 	if len(iso) < 10 {
-		return nil, Data_Error{msg = "format may only be used on dates", pos = pos}
+		return nil, Error_Body{
+			msg = "format may only be used on dates",
+			pos = pos,
+			kind = .Data,
+		}
 	}
 
 	year := iso[:4]
@@ -154,7 +165,11 @@ apply_format :: proc(iso: string, args: []string, pos: int) -> (result: any, err
 	day_num := (int(iso[8]) - 0x30) * 10 + (int(iso[9]) - 0x30)
 
 	if month_num < 1 || month_num > 12 {
-		return nil, Data_Error{msg = fmt.tprintf("invalid date: \"%s\"", iso), pos = pos}
+		return nil, Error_Body{
+			msg = fmt.tprintf("invalid date: \"%s\"", iso),
+			pos = pos,
+			kind = .Data,
+		}
 	}
 
 	month := fmt.tprintf("%s", time.Month(month_num))[:3]
@@ -162,20 +177,22 @@ apply_format :: proc(iso: string, args: []string, pos: int) -> (result: any, err
 }
 
 // Groups preserve first-appearance order from the input list.
-apply_group_by :: proc(value: any, args: []string, pos: int) -> (result: any, err: Render_Error) {
+apply_group_by :: proc(value: any, args: []string, pos: int) -> (result: any, err: Error) {
 	if len(args) != 1 {
-		return nil, Data_Error{
+		return nil, Error_Body{
 			msg = fmt.tprintf("group_by expects 1 argument, got %d", len(args)),
 			pos = pos,
+			kind = .Data,
 		}
 	}
 	field := args[0]
 
 	elem_info, count, data := list_info(value)
 	if elem_info == nil {
-		return nil, Data_Error{
+		return nil, Error_Body{
 			msg = "group_by expects a list",
 			pos = pos,
+			kind = .Data,
 		}
 	}
 
@@ -189,16 +206,18 @@ apply_group_by :: proc(value: any, args: []string, pos: int) -> (result: any, er
 
 		key_val, found := lookup_in(elem, field)
 		if !found {
-			return nil, Data_Error {
+			return nil, Error_Body {
 				msg = fmt.tprintf("group_by: element missing field '%s'", field),
 				pos = pos,
+				kind = .Data,
 			}
 		}
 		key_str := any_to_string(key_val)
 		if len(key_str) == 0 {
-			return nil, Data_Error{
+			return nil, Error_Body{
 				msg = fmt.tprintf("group_by: field '%s' is empty", field),
 				pos = pos,
+				kind = .Data,
 			}
 		}
 

mustache/pipes_test.odin

@@ -66,13 +66,9 @@ test_pipe_group_by_missing_field_fails :: proc(t: ^testing.T) {
 	defer delete_template(&tpl)
 	_, err := render(tpl, data)
 	testing.expect(t, err != nil, "missing field should error")
-
+	b := body(err)
-	is_data_err := false
+	testing.expect(t, b.kind == .Data, "error should be Data kind")
-	#partial switch e in err {
+	testing.expect(t, len(b.msg) > 0, "error should have non-empty msg")
-	case Data_Error:
-		is_data_err = len(e.msg) > 0
-	}
-	testing.expect(t, is_data_err, "error should be Data_Error")
 }
 
 @(test)

mustache/tokenizer.odin

@@ -28,7 +28,7 @@ tokenize :: proc(
 	allocator := context.allocator,
 ) -> (
 	tokens: [dynamic]Token,
-	err: Render_Error,
+	err: Error,
 ) {
 	tokens = make([dynamic]Token, 0, 8, allocator)
 
@@ -47,9 +47,10 @@ tokenize :: proc(
 				content_start := i + 3
 				idx := strings.index(src[content_start:], "}}}")
 				if idx < 0 {
-					return tokens, Syntax_Error {
+					return tokens, Error_Body {
 						msg = "unclosed triple mustache '{{{'",
 						pos = tag_pos,
+						kind = .Syntax,
 					}
 				}
 				close := content_start + idx
@@ -90,7 +91,11 @@ tokenize :: proc(
 
 				close_idx := strings.index(src[key_start:], "}}")
 			if close_idx < 0 {
-					return tokens, Syntax_Error{msg = "unclosed tag '{{'", pos = tag_pos}
+				return tokens, Error_Body {
+					msg = "unclosed tag '{{'",
+					pos = tag_pos,
+					kind = .Syntax,
+				}
 			}
 				close := key_start + close_idx
 

render.odin

@@ -63,31 +63,17 @@ load_template :: proc(vfs: ^VFS, virtual_path: string) -> mustache.Template {
 	source := string(data)
 	tpl, err := mustache.parse(source, entry.fs_path)
 	if err != nil {
-		switch e in err {
+		b := mustache.body(err)
-		// TODO: Find a way to merge these branches.
-		case mustache.Syntax_Error:
 		log.errorf(
 			"%s",
 			mustache.format_error(
 				entry.fs_path,
 				source,
-					e.pos,
+				b.pos,
-					e.msg,
+				b.msg,
 				colorize = mustache.should_colorize(),
 			),
 		)
-		case mustache.Data_Error:
-			log.errorf(
-				"%s",
-				mustache.format_error(
-					entry.fs_path,
-					source,
-					e.pos,
-					e.msg,
-					colorize = mustache.should_colorize(),
-				),
-			)
-		}
 		os.exit(1)
 	}
 	return tpl
@@ -375,31 +361,17 @@ load_partials :: proc(vfs: ^VFS) -> map[string]mustache.Template {
 		source := string(data)
 		tpl, err := mustache.parse(source, entry.fs_path)
 		if err != nil {
-			// TODO: Find a way to merge these branches.
+			b := mustache.body(err)
-			switch e in err {
-			case mustache.Syntax_Error:
 			log.errorf(
 				"%s",
 				mustache.format_error(
 					entry.fs_path,
 					source,
-						e.pos,
+					b.pos,
-						e.msg,
+					b.msg,
 					colorize = mustache.should_colorize(),
 				),
 			)
-			case mustache.Data_Error:
-				log.errorf(
-					"%s",
-					mustache.format_error(
-						entry.fs_path,
-						source,
-						e.pos,
-						e.msg,
-						colorize = mustache.should_colorize(),
-					),
-				)
-			}
 			os.exit(1)
 		}
 		partials[key] = tpl