Implement tern template support

internal/compiler/compile.go

@@ -38,6 +38,11 @@ func (c *Compiler) parseCatalog(schemas []string) error {
 			continue
 		}
 		contents := migrations.RemoveRollbackStatements(string(blob))
+		contents, err = migrations.TransformStatements(filepath.Dir(filename), contents)
+		if err != nil {
+			merr.Add(filename, contents, 0, err)
+			continue
+		}
 		c.schema = append(c.schema, contents)
 		stmts, err := c.parser.Parse(strings.NewReader(contents))
 		if err != nil {

internal/migrations/migrations.go

@@ -2,6 +2,11 @@ package migrations
 
 import (
 	"bufio"
+	"errors"
+	"fmt"
+	"os"
+	"path"
+	"regexp"
 	"strings"
 )
 
@@ -37,3 +42,38 @@ func IsDown(filename string) bool {
 	// Remove golang-migrate rollback files.
 	return strings.HasSuffix(filename, ".down.sql")
 }
+
+var ternTemplateRegex *regexp.Regexp
+
+// tern: {{ template "filepath" . }}
+func TransformStatements(pwd, content string) (string, error) {
+	if !strings.Contains(content, "{{ template \"") {
+		return content, nil
+	}
+
+	var err error
+	var processed string
+
+	if ternTemplateRegex == nil {
+		defer func() {
+			if r := recover(); r != nil {
+				fmt.Printf("failed to compile regexp: %v\n", r)
+			}
+			// It is tested, just recovering for it's technically possible to panic
+		}()
+		ternTemplateRegex = regexp.MustCompile(`\{\{ template \"(.+)\" \. \}\}`)
+	}
+
+	processed = ternTemplateRegex.ReplaceAllStringFunc(content, func(match string) string {
+		filePath := ternTemplateRegex.FindStringSubmatch(match)[1]
+		filePath = path.Join(pwd, filePath)
+		read, err := os.ReadFile(filePath)
+		if err != nil {
+			err = errors.Join(err, fmt.Errorf("error reading file %s: %w", filePath, err))
+			return match
+		}
+		return string(read)
+	})
+
+	return processed, err
+}