add redundant-return diagnostic

Author: Cr4xy

locale/en-us/script.lua

@@ -42,6 +42,7 @@ DIAG_COUNT_DOWN_LOOP = 'Do you mean `{}` ?'
 DIAG_IMPLICIT_ANY = 'Can not infer type.'
 DIAG_DEPRECATED = 'Deprecated.'
 DIAG_DIFFERENT_REQUIRES = 'The same file is required with different names.'
+DIAG_REDUNDANT_RETURN = 'Redundant return.'
 
 DIAG_CIRCLE_DOC_CLASS = 'Circularly inherited classes.'
 DIAG_DOC_FIELD_NO_CLASS = 'The field must be defined after the class.'

locale/zh-cn/script.lua

@@ -42,6 +42,7 @@ DIAG_COUNT_DOWN_LOOP = '你的意思是 `{}` 吗？'
 DIAG_IMPLICIT_ANY = '无法推测出类型。'
 DIAG_DEPRECATED = '已废弃。'
 DIAG_DIFFERENT_REQUIRES = '使用了不同的名字 require 了同一个文件。'
+DIAG_REDUNDANT_RETURN = '冗余返回。'
 
 DIAG_CIRCLE_DOC_CLASS = '循环继承的类。'
 DIAG_DOC_FIELD_NO_CLASS = '字段必须定义在类之后。'

script/core/diagnostics/redundant-return.lua

@@ -0,0 +1,32 @@
+local files = require 'files'
+local guide = require 'parser.guide'
+local lang = require 'language'
+local define = require 'proto.define'
+
+-- reports 'return' or 'return nil' at the end of functions
+return function (uri, callback)
+ local ast = files.getState(uri)
+ if not ast then
+ return
+ end
+
+ guide.eachSourceType(ast.ast, 'return', function (source)
+ if not source.parent or source.parent.type ~= "function" then
+ return
+ end
+ for _, node in ipairs(source) do
+ while node and node.type == "paren" do
+ node = node.exp
+ end
+ if node and (node.type ~= "nil" or #node > 0) then
+ return
+ end
+ end
+ callback {
+ start = source.start,
+ finish = source.finish,
+ tags = { define.DiagnosticTag.Unnecessary },
+ message = lang.script.DIAG_REDUNDANT_RETURN,
+ }
+ end)
+end

script/proto/define.lua

@@ -29,6 +29,7 @@ m.DiagnosticDefaultSeverity = {
  ['newline-call'] = 'Information',
  ['newfield-call'] = 'Warning',
  ['redundant-parameter'] = 'Warning',
+ ['redundant-return'] = 'Warning',
  ['ambiguity-1'] = 'Warning',
  ['lowercase-global'] = 'Information',
  ['undefined-env-child'] = 'Information',
@@ -82,6 +83,7 @@ m.DiagnosticDefaultNeededFileStatus = {
  ['newline-call'] = 'Any',
  ['newfield-call'] = 'Any',
  ['redundant-parameter'] = 'Opened',
+ ['redundant-return'] = 'Opened',
  ['ambiguity-1'] = 'Any',
  ['lowercase-global'] = 'Any',
  ['undefined-env-child'] = 'Any',