feat: allow setting empty env var value

conf.v

@@ -17,20 +17,18 @@ pub struct LoadConfig {
 // looks for either `${env.prefix}${field_name.to_upper()}` or
 // `${env.prefix}${field_name.to_upper()}${env.file_suffix}`, returning the
 // contents of the file instead if the latter. If both or neither exist, the
-// function returns an error.
-fn (ld LoadConfig) get_env_var(field_name string) !string {
+// function returns an error. It returns two values, with the first indicating
+// whether the env vars were actually present.
+fn (ld LoadConfig) get_env_var(field_name string) !(bool, string) {
 	env_var_name := '$ld.prefix$field_name.to_upper()'
 	env_file_name := '$ld.prefix$field_name.to_upper()$ld.file_suffix'
-	env_var := ld.env[env_var_name] or { '' }
-	env_file := ld.env[env_file_name] or { '' }
 
-	// If both are missing, we return an empty string
-	if env_var == '' && env_file == '' {
-		return ''
+	if env_var_name !in ld.env && env_file_name !in ld.env {
+		return false, ''
 	}
 
 	// If they're both set, we report a conflict
-	if env_var != '' && env_file != '' {
+	if env_var_name in ld.env && env_file_name in ld.env {
 		return error('Only one of $env_var_name or $env_file_name can be defined.')
 	}
 
@@ -38,12 +36,12 @@ fn (ld LoadConfig) get_env_var(field_name string) !string {
 	// I'm pretty sure this also prevents variable ending in _FILE (e.g.
 	// VIETER_LOG_FILE) from being mistakingely read as an _FILE suffixed env
 	// var.
-	if env_var != '' {
-		return env_var
+	if env_var_name in ld.env {
+		return true, ld.env[env_var_name]
 	}
 
 	// Otherwise, we process the file
-	return os.read_file(env_file) or {
+	return true, os.read_file(ld.env[env_file_name]) or {
 		error('Failed to read file defined in $env_file_name: ${err.msg()}.')
 	}
 }
@@ -86,11 +84,11 @@ pub fn load<T>(ld LoadConfig) !T {
 	}
 
 	$for field in T.fields {
-		env_value := ld.get_env_var(field.name)!
+		env_present, env_value := ld.get_env_var(field.name)!
 
 		// The value of an env var will always take precedence over the toml
 		// file.
-		if env_value != '' {
+		if env_present {
 			$if field.typ is string {
 				res.$(field.name) = env_value
 			} $else $if field.typ is int {

string_test.v

@@ -8,29 +8,47 @@ struct SingleConfDefault {
 	some_string string = 'default'
 }
 
-const env = {
-	'SOME_STRING': 'env'
-}
-
-const prefix_env = {
-	'TEST_SOME_STRING': 'env'
-}
-
 fn test_string_present_no_default() {
 	conf := load<SingleConf>(default_path: 'test/string.toml')!
 	assert conf == SingleConf{
 		some_string: 'hi'
 	}
+
+	conf2 := load<SingleConf>(default_path: 'test/string_empty.toml')!
+	assert conf2 == SingleConf{
+		some_string: ''
+	}
 }
 
 fn test_string_present_no_default_env() {
-	conf := load<SingleConf>(default_path: 'test/string.toml', env: .env)!
+	mut conf := load<SingleConf>(
+		default_path: 'test/string.toml'
+		env: {
+			'SOME_STRING': 'env'
+		}
+	)!
 	assert conf == SingleConf{
 		some_string: 'env'
 	}
 
-	conf2 := load<SingleConf>(default_path: 'test/string.toml', env: .prefix_env, prefix: 'TEST_')!
-	assert conf2 == SingleConf{
+	conf = load<SingleConf>(
+		default_path: 'test/string.toml'
+		env: {
+			'SOME_STRING': ''
+		}
+	)!
+	assert conf == SingleConf{
+		some_string: ''
+	}
+
+	conf = load<SingleConf>(
+		default_path: 'test/string.toml'
+		env: {
+			'TEST_SOME_STRING': 'env'
+		}
+		prefix: 'TEST_'
+	)!
+	assert conf == SingleConf{
 		some_string: 'env'
 	}
 }
@@ -41,13 +59,34 @@ fn test_string_absent_no_default() {
 }
 
 fn test_string_absent_no_default_env() {
-	conf := load<SingleConf>(default_path: 'test/string.toml', env: .env)!
+	mut conf := load<SingleConf>(
+		default_path: 'test/string.toml'
+		env: {
+			'SOME_STRING': 'env'
+		}
+	)!
 	assert conf == SingleConf{
 		some_string: 'env'
 	}
 
-	conf2 := load<SingleConf>(default_path: 'test/string.toml', env: .prefix_env, prefix: 'TEST_')!
-	assert conf2 == SingleConf{
+	conf = load<SingleConf>(
+		default_path: 'test/string.toml'
+		env: {
+			'SOME_STRING': ''
+		}
+	)!
+	assert conf == SingleConf{
+		some_string: ''
+	}
+
+	conf = load<SingleConf>(
+		default_path: 'test/string.toml'
+		env: {
+			'TEST_SOME_STRING': 'env'
+		}
+		prefix: 'TEST_'
+	)!
+	assert conf == SingleConf{
 		some_string: 'env'
 	}
 }
@@ -60,17 +99,34 @@ fn test_string_present_default() {
 }
 
 fn test_string_present_default_env() {
-	conf := load<SingleConfDefault>(default_path: 'test/string.toml', env: .env)!
+	mut conf := load<SingleConfDefault>(
+		default_path: 'test/string.toml'
+		env: {
+			'SOME_STRING': 'env'
+		}
+	)!
 	assert conf == SingleConfDefault{
 		some_string: 'env'
 	}
 
-	conf2 := load<SingleConfDefault>(
+	conf = load<SingleConfDefault>(
 		default_path: 'test/string.toml'
-		env: .prefix_env
+		env: {
+			'SOME_STRING': ''
+		}
+	)!
+	assert conf == SingleConfDefault{
+		some_string: ''
+	}
+
+	conf = load<SingleConfDefault>(
+		default_path: 'test/string.toml'
+		env: {
+			'TEST_SOME_STRING': 'env'
+		}
 		prefix: 'TEST_'
 	)!
-	assert conf2 == SingleConfDefault{
+	assert conf == SingleConfDefault{
 		some_string: 'env'
 	}
 }
@@ -83,17 +139,34 @@ fn test_string_absent_default() {
 }
 
 fn test_string_absent_default_env() {
-	conf := load<SingleConfDefault>(default_path: 'test/empty.toml', env: .env)!
+	mut conf := load<SingleConfDefault>(
+		default_path: 'test/empty.toml'
+		env: {
+			'SOME_STRING': 'env'
+		}
+	)!
 	assert conf == SingleConfDefault{
 		some_string: 'env'
 	}
 
-	conf2 := load<SingleConfDefault>(
+	conf = load<SingleConfDefault>(
 		default_path: 'test/empty.toml'
-		env: .prefix_env
+		env: {
+			'SOME_STRING': ''
+		}
+	)!
+	assert conf == SingleConfDefault{
+		some_string: ''
+	}
+
+	conf = load<SingleConfDefault>(
+		default_path: 'test/empty.toml'
+		env: {
+			'TEST_SOME_STRING': 'env'
+		}
 		prefix: 'TEST_'
 	)!
-	assert conf2 == SingleConfDefault{
+	assert conf == SingleConfDefault{
 		some_string: 'env'
 	}
 }

test/int.toml

@@ -0,0 +1 @@
+some_int = "hi"

test/string_empty.toml

@@ -0,0 +1 @@
+some_string = ""