2 files changed, 69 insertions, 0 deletions
diff --git a/script/core/diagnostics/unreachable-code.lua b/script/core/diagnostics/unreachable-code.lua
new file mode 100644
index 00000000..28aee6ea
--- /dev/null
+++ b/script/core/diagnostics/unreachable-code.lua
@@ -0,0 +1,68 @@
+local files  = require 'files'
+local guide  = require 'parser.guide'
+local vm     = require 'vm'
+local lang   = require 'language'
+local await  = require 'await'
+
+---@param block parser.object
+---@return boolean
+local function hasReturn(block)
+    if block.hasReturn or block.hasError then
+        return true
+    end
+    if block.type == 'if' then
+        local hasElse
+        for _, subBlock in ipairs(block) do
+            if not hasReturn(subBlock) then
+                return false
+            end
+            if subBlock.type == 'elseblock' then
+                hasElse = true
+            end
+        end
+        return hasElse == true
+    else
+        if block.type == 'while' then
+            if vm.testCondition(block.filter) then
+                return true
+            end
+        end
+        for _, action in ipairs(block) do
+            if guide.isBlockType(action) then
+                if hasReturn(action) then
+                    return true
+                end
+            end
+        end
+    end
+    return false
+end
+
+---@async
+return function (uri, callback)
+    local state = files.getState(uri)
+    if not state then
+        return
+    end
+
+    ---@async
+    guide.eachSourceTypes(state.ast, {'main', 'function'}, function (source)
+        await.delay()
+        if not source.returns then
+            return
+        end
+        for i, action in ipairs(source) do
+            if  guide.isBlockType(action)
+            and hasReturn(action) then
+                if i < #source then
+                    callback {
+                        start = source[i+1].start,
+                        finish = source[#source].finish,
+                        message = lang.script('DIAG_UNREACHABLE_CODE'),
+                    }
+                end
+                return
+            end
+        end
+    end)
+end
diff --git a/script/proto/diagnostic.lua b/script/proto/diagnostic.lua
index d8312dfe..dc550fac 100644
--- a/script/proto/diagnostic.lua
+++ b/script/proto/diagnostic.lua
@@ -47,6 +47,7 @@ m.register {
     'redundant-return',
     'empty-block',
     'code-after-break',
+    'unreachable-code',
 } {
     group    = 'unused',
     severity = 'Hint',