fix: auto-detect schema from dump file header for plan/apply (#296)

cmd/apply/apply.go

@@ -265,14 +265,23 @@ func RunApply(cmd *cobra.Command, args []string) error {
 		}
 	}
 
+	// Auto-detect schema from dump file if --schema was not explicitly set
+	effectiveSchema := applySchema
+	if !cmd.Flags().Changed("schema") && applyFile != "" {
+		if detected, err := util.DetectSchemaFromFile(applyFile); err == nil && detected != "" {
+			effectiveSchema = detected
+			fmt.Fprintf(os.Stderr, "Auto-detected schema '%s' from dump file\n", detected)
+		}
+	}
+
 	// Build configuration
 	config := &ApplyConfig{
 		Host:            applyHost,
 		Port:            applyPort,
 		DB:              applyDB,
 		User:            applyUser,
 		Password:        finalPassword,
-		Schema:          applySchema,
+		Schema:          effectiveSchema,
 		AutoApprove:     applyAutoApprove,
 		NoColor:         applyNoColor,
 		LockTimeout:     applyLockTimeout,

cmd/dump/dump_integration_test.go

@@ -356,16 +356,17 @@ func runTenantSchemaTest(t *testing.T, testDataDir string) {
 	}
 }
 
-// normalizeSchemaOutput removes version-specific lines for comparison.
-// This allows comparing dumps across different PostgreSQL versions.
+// normalizeSchemaOutput removes version-specific and metadata lines for comparison.
+// This allows comparing dumps across different PostgreSQL versions and schema contexts.
 func normalizeSchemaOutput(output string) string {
 	lines := strings.Split(output, "\n")
 	var normalizedLines []string
 
 	for _, line := range lines {
-		// Skip version-related lines
+		// Skip version-related and metadata lines
 		if strings.Contains(line, "-- Dumped by pgschema version") ||
-			strings.Contains(line, "-- Dumped from database version") {
+			strings.Contains(line, "-- Dumped from database version") ||
+			strings.Contains(line, "-- Dumped from schema:") {
 			continue
 		}
 		normalizedLines = append(normalizedLines, line)

cmd/plan/plan.go

@@ -101,14 +101,23 @@ func runPlan(cmd *cobra.Command, args []string) error {
 		}
 	}
 
+	// Auto-detect schema from dump file if --schema was not explicitly set
+	effectiveSchema := planSchema
+	if !cmd.Flags().Changed("schema") && planFile != "" {
+		if detected, err := util.DetectSchemaFromFile(planFile); err == nil && detected != "" {
+			effectiveSchema = detected
+			fmt.Fprintf(os.Stderr, "Auto-detected schema '%s' from dump file\n", detected)
+		}
+	}
+
 	// Create plan configuration
 	config := &PlanConfig{
 		Host:            planHost,
 		Port:            planPort,
 		DB:              planDB,
 		User:            planUser,
 		Password:        finalPassword,
-		Schema:          planSchema,
+		Schema:          effectiveSchema,
 		File:            planFile,
 		ApplicationName: "pgschema",
 		// Plan database configuration

cmd/util/schema_detect.go

@@ -0,0 +1,36 @@
+package util
+
+import (
+	"bufio"
+	"io"
+	"os"
+	"strings"
+)
+
+const schemaHeaderPrefix = "-- Dumped from schema: "
+
+// DetectSchemaFromFile reads the header of a SQL dump file and extracts the
+// schema name from the "-- Dumped from schema: <name>" metadata line.
+// Returns empty string if the header is not found.
+func DetectSchemaFromFile(filePath string) (string, error) {
+	f, err := os.Open(filePath)
+	if err != nil {
+		return "", err
+	}
+	defer f.Close()
+
+	return detectSchemaFromReader(f)
+}
+
+// detectSchemaFromReader reads from an io.Reader and extracts the schema name
+// from the pgschema dump header. Only scans the first 20 lines (header area).
+func detectSchemaFromReader(r io.Reader) (string, error) {
+	scanner := bufio.NewScanner(r)
+	for i := 0; i < 20 && scanner.Scan(); i++ {
+		line := scanner.Text()
+		if strings.HasPrefix(line, schemaHeaderPrefix) {
+			return strings.TrimSpace(line[len(schemaHeaderPrefix):]), nil
+		}
+	}
+	return "", scanner.Err()
+}

cmd/util/schema_detect_test.go

@@ -0,0 +1,87 @@
+package util
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestDetectSchemaFromReader(t *testing.T) {
+	tests := []struct {
+		name     string
+		content  string
+		expected string
+	}{
+		{
+			name: "public schema",
+			content: `--
+-- pgschema database dump
+--
+
+-- Dumped from database version PostgreSQL 17.7
+-- Dumped by pgschema version 1.7.1
+-- Dumped from schema: public
+
+`,
+			expected: "public",
+		},
+		{
+			name: "non-public schema",
+			content: `--
+-- pgschema database dump
+--
+
+-- Dumped from database version PostgreSQL 17.7
+-- Dumped by pgschema version 1.7.1
+-- Dumped from schema: vehicle
+
+`,
+			expected: "vehicle",
+		},
+		{
+			name: "quoted schema name",
+			content: `--
+-- pgschema database dump
+--
+
+-- Dumped from database version PostgreSQL 17.7
+-- Dumped by pgschema version 1.7.1
+-- Dumped from schema: my_schema
+
+`,
+			expected: "my_schema",
+		},
+		{
+			name: "no schema header (old dump format)",
+			content: `--
+-- pgschema database dump
+--
+
+-- Dumped from database version PostgreSQL 17.7
+-- Dumped by pgschema version 1.7.1
+
+
+CREATE TABLE IF NOT EXISTS users (
+    id integer NOT NULL
+);
+`,
+			expected: "",
+		},
+		{
+			name:     "empty file",
+			content:  "",
+			expected: "",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result, err := detectSchemaFromReader(strings.NewReader(tt.content))
+			if err != nil {
+				t.Fatalf("unexpected error: %v", err)
+			}
+			if result != tt.expected {
+				t.Errorf("got %q, want %q", result, tt.expected)
+			}
+		})
+	}
+}

internal/diff/header.go

@@ -1,25 +1 @@
 package diff
-
-import (
-	"fmt"
-	"strings"
-
-	"github.com/pgplex/pgschema/internal/version"
-	"github.com/pgplex/pgschema/ir"
-)
-
-// GenerateDumpHeader generates the header for database dumps with metadata
-func GenerateDumpHeader(schemaIR *ir.IR) string {
-	var header strings.Builder
-
-	header.WriteString("--\n")
-	header.WriteString("-- pgschema database dump\n")
-	header.WriteString("--\n")
-	header.WriteString("\n")
-
-	header.WriteString(fmt.Sprintf("-- Dumped from database version %s\n", schemaIR.Metadata.DatabaseVersion))
-	header.WriteString(fmt.Sprintf("-- Dumped by pgschema version %s\n", version.App()))
-	header.WriteString("\n")
-	header.WriteString("\n")
-	return header.String()
-}

internal/dump/formatter.go

@@ -179,6 +179,7 @@ func (f *DumpFormatter) generateDumpHeader() string {
 
 	header.WriteString(fmt.Sprintf("-- Dumped from database version %s\n", f.dbVersion))
 	header.WriteString(fmt.Sprintf("-- Dumped by pgschema version %s\n", version.App()))
+	header.WriteString(fmt.Sprintf("-- Dumped from schema: %s\n", f.targetSchema))
 	header.WriteString("\n")
 	header.WriteString("\n")
 	return header.String()