new diagnostic: `need-check-nil`

7 files changed, 86 insertions, 11 deletions

diff --git a/changelog.md b/changelog.md
index eb1aaf78..ff2d2c1e 100644
--- a/changelog.md
+++ b/changelog.md
@@ -26,6 +26,7 @@
 * `NEW` generic: resolve `T[]` by `table<integer, type>` or `---@field [integer] type`
 * `NEW` resolve `class[1]` by `---@field [integer] type`
 * `NEW` diagnostic: `missing-parameter`
+* `NEW` diagnostic: `need-check-nil`
 * `CHG` diagnostic: no longer mark `redundant-parameter` as `Unnecessary`
 * `FIX` diagnostic: `unused-function` does not recognize recursion
 * `FIX` [#1051](https://github.com/sumneko/lua-language-server/issues/1051)
diff --git a/script/core/diagnostics/need-check-nil.lua b/script/core/diagnostics/need-check-nil.lua
new file mode 100644
index 00000000..8654a7a6
--- /dev/null
+++ b/script/core/diagnostics/need-check-nil.lua
@@ -0,0 +1,39 @@
+local files = require 'files'
+local guide = require 'parser.guide'
+local vm    = require 'vm'
+local lang  = require 'language'
+
+return function (uri, callback)
+    local state = files.getState(uri)
+    if not state then
+        return
+    end
+
+    guide.eachSourceType(state.ast, 'getlocal', function (src)
+        local checkNil
+        local nxt = src.next
+        if nxt then
+            if nxt.type == 'getfield'
+            or nxt.type == 'getmethod'
+            or nxt.type == 'getindex'
+            or nxt.type == 'call' then
+                checkNil = true
+            end
+        end
+        local call = src.parent
+        if call and call.type == 'call' and call.node == src then
+            checkNil = true
+        end
+        if not checkNil then
+            return
+        end
+        local node = vm.compileNode(src)
+        if node:hasFalsy() then
+            callback {
+                start   = src.start,
+                finish  = src.finish,
+                message = lang.script('DIAG_MISS_NEED_CHECK_NIL'),
+            }
+        end
+    end)
+end
diff --git a/script/proto/define.lua b/script/proto/define.lua
index 9da67039..fb60c56c 100644
--- a/script/proto/define.lua
+++ b/script/proto/define.lua
@@ -9,10 +9,10 @@ m.DiagnosticSeverity = {
 }
 
 ---@alias DiagnosticDefaultSeverity
----| '"Hint"'
----| '"Information"'
----| '"Warning"'
----| '"Error"'
+---| 'Hint'
+---| 'Information'
+---| 'Warning'
+---| 'Error'
 
 --- 诊断类型与默认等级
 ---@type table<string, DiagnosticDefaultSeverity>
@@ -48,6 +48,7 @@ m.DiagnosticDefaultSeverity = {
     ['await-in-sync']           = 'Warning',
     ['not-yieldable']           = 'Warning',
     ['discard-returns']         = 'Warning',
+    ['need-check-nil']          = 'Warning',
     ['type-check']              = 'Warning',
 
     ['duplicate-doc-alias']     = 'Warning',
@@ -64,9 +65,9 @@ m.DiagnosticDefaultSeverity = {
 }
 
 ---@alias DiagnosticDefaultNeededFileStatus
----| '"Any"'
----| '"Opened"'
----| '"None"'
+---| 'Any'
+---| 'Opened'
+---| 'None'
 
 -- 文件状态
 m.FileStatus = {
@@ -108,6 +109,7 @@ m.DiagnosticDefaultNeededFileStatus = {
     ['await-in-sync']           = 'None',
     ['not-yieldable']           = 'None',
     ['discard-returns']         = 'Opened',
+    ['need-check-nil']          = 'Opened',
     ['type-check']              = 'None',
 
     ['duplicate-doc-alias']     = 'Any',
diff --git a/script/vm/compiler.lua b/script/vm/compiler.lua
index 4917d33a..1f33a784 100644
--- a/script/vm/compiler.lua
+++ b/script/vm/compiler.lua
@@ -1435,9 +1435,8 @@ local compilerSwitch = util.switch()
             elseif r1 == false then
                 vm.setNode(source, node1)
             else
-                vm.getNode(source):merge(node1)
-                vm.getNode(source):setTruly()
                 vm.getNode(source):merge(node2)
+                vm.getNode(source):addOptional()
             end
         end
         if source.op.type == 'or' then
diff --git a/script/vm/node.lua b/script/vm/node.lua
index d52c2a84..06023ca5 100644
--- a/script/vm/node.lua
+++ b/script/vm/node.lua
@@ -80,7 +80,7 @@ function mt:isOptional()
 end
 
 ---@return boolean
-function mt:isFalsy()
+function mt:hasFalsy()
     if self.optional then
         return true
     end
diff --git a/script/vm/sign.lua b/script/vm/sign.lua
index 78d61022..795916fa 100644
--- a/script/vm/sign.lua
+++ b/script/vm/sign.lua
@@ -128,7 +128,7 @@ function mt:resolve(uri, args, removeGeneric)
     local function buildArgNode(argNode, knownTypes)
         local newArgNode = vm.createNode()
         for n in argNode:eachObject() do
-            if argNode:isFalsy() then
+            if argNode:hasFalsy() then
                 goto CONTINUE
             end
             local view = infer.viewObject(n)
diff --git a/test/diagnostics/common.lua b/test/diagnostics/common.lua
index dca826a1..72b2db6c 100644
--- a/test/diagnostics/common.lua
+++ b/test/diagnostics/common.lua
@@ -1460,3 +1460,37 @@ end
 
 <!T:ff!>()
 ]]
+
+TEST [[
+---@type string?
+local x
+
+S = <!x!>:upper()
+]]
+
+TEST [[
+---@type string?
+local x
+
+if x then
+    S = x:upper()
+end
+]]
+
+TEST [[
+---@type string?
+local x
+
+if not x then
+    x = ''
+end
+
+S = x:upper()
+]]
+
+TEST [[
+---@type fun()?
+local x
+
+S = <!x!>()
+]]