fix: order SQL functions after relation creation

internal/migration_acceptance_tests/function_cases_test.go

@@ -72,6 +72,20 @@ var functionAcceptanceTestCases = []acceptanceTestCase{
 			`,
 		},
 	},
+	{
+		name:         "Create sql function after table referenced by body",
+		oldSchemaDDL: nil,
+		newSchemaDDL: []string{
+			`
+			CREATE SCHEMA app;
+			CREATE TABLE app.dead_letter(id int);
+			CREATE FUNCTION app.record_dead_letter()
+			RETURNS void
+			LANGUAGE sql
+			AS $$ INSERT INTO app.dead_letter(id) VALUES (1) $$;
+			`,
+		},
+	},
 	{
 		name:         "Create functions with quoted names (with conflicting names)",
 		oldSchemaDDL: nil,

pkg/diff/function_sql_vertex_generator.go

@@ -11,11 +11,13 @@ type functionSQLVertexGenerator struct {
 	// functionsInNewSchemaByName is a map of function name to functions in the new schema.
 	// These functions are not necessarily new
 	functionsInNewSchemaByName map[string]schema.Function
+	newSchema                  schema.Schema
 }
 
-func newFunctionSqlVertexGenerator(functionsInNewSchemaByName map[string]schema.Function) sqlVertexGenerator[schema.Function, functionDiff] {
+func newFunctionSqlVertexGenerator(functionsInNewSchemaByName map[string]schema.Function, newSchema schema.Schema) sqlVertexGenerator[schema.Function, functionDiff] {
 	return legacyToNewSqlVertexGenerator[schema.Function, functionDiff](&functionSQLVertexGenerator{
 		functionsInNewSchemaByName: functionsInNewSchemaByName,
+		newSchema:                  newSchema,
 	})
 }
 
@@ -86,6 +88,9 @@ func (f *functionSQLVertexGenerator) GetAddAlterDependencies(newFunction, oldFun
 	for _, depFunction := range newFunction.DependsOnFunctions {
 		deps = append(deps, mustRun(f.GetSQLVertexId(newFunction, diffTypeAddAlter)).after(buildFunctionVertexId(depFunction, diffTypeAddAlter)))
 	}
+	if canFunctionDependenciesBeTracked(newFunction) {
+		deps = append(deps, f.getRelationAddAlterDependencies(newFunction)...)
+	}
 
 	if !cmp.Equal(oldFunction, schema.Function{}) {
 		// If the function is being altered:
@@ -106,3 +111,20 @@ func (f *functionSQLVertexGenerator) GetDeleteDependencies(function schema.Funct
 	}
 	return deps, nil
 }
+
+func (f *functionSQLVertexGenerator) getRelationAddAlterDependencies(function schema.Function) []dependency {
+	var deps []dependency
+
+	// SQL functions validate table and sequence references in their body at
+	// CREATE time, but PostgreSQL does not expose those body relation references
+	// as pg_proc -> pg_class dependencies in pg_depend. Keep this deliberately
+	// broad, mirroring the procedure generator's best-effort relation ordering.
+	for _, table := range f.newSchema.Tables {
+		deps = append(deps, mustRun(f.GetSQLVertexId(function, diffTypeAddAlter)).after(buildTableVertexId(table.SchemaQualifiedName, diffTypeAddAlter)))
+	}
+	for _, seq := range f.newSchema.Sequences {
+		deps = append(deps, mustRun(f.GetSQLVertexId(function, diffTypeAddAlter)).after(buildSequenceVertexId(seq.SchemaQualifiedName, diffTypeAddAlter)))
+	}
+
+	return deps
+}

pkg/diff/sql_generator.go

@@ -653,7 +653,7 @@ func (s schemaSQLGenerator) Alter(diff schemaDiff) ([]Statement, error) {
 	}
 	partialGraph = concatPartialGraphs(partialGraph, sequenceOwnershipsPartialGraph)
 
-	functionGenerator := newFunctionSqlVertexGenerator(functionsInNewSchemaByName)
+	functionGenerator := newFunctionSqlVertexGenerator(functionsInNewSchemaByName, diff.new)
 	functionsPartialGraph, err := generatePartialGraph(functionGenerator, diff.functionDiffs)
 	if err != nil {
 		return nil, fmt.Errorf("resolving function diff: %w", err)