diagnostic `missing-return-value`

4 files changed, 78 insertions, 13 deletions

diff --git a/script/core/diagnostics/missing-return-value.lua b/script/core/diagnostics/missing-return-value.lua
new file mode 100644
index 00000000..491475c7
--- /dev/null
+++ b/script/core/diagnostics/missing-return-value.lua
@@ -0,0 +1,62 @@
+local files  = require 'files'
+local guide  = require 'parser.guide'
+local vm     = require 'vm'
+local lang   = require 'language'
+
+local function hasDocReturn(func)
+    if not func.bindDocs then
+        return false
+    end
+    for _, doc in ipairs(func.bindDocs) do
+        if doc.type == 'doc.return' then
+            return true
+        end
+    end
+    return false
+end
+
+return function (uri, callback)
+    local state = files.getState(uri)
+    if not state then
+        return
+    end
+
+    guide.eachSourceType(state.ast, 'function', function (source)
+        if not hasDocReturn(source) then
+            return
+        end
+        local min = vm.countReturnsOfFunction(source)
+        if min == 0 then
+            return
+        end
+        local returns = source.returns
+        if not returns then
+            return
+        end
+        for _, ret in ipairs(returns) do
+            local rmin, rmax = vm.countList(ret)
+            if rmax < min then
+                if rmin == rmax then
+                    callback {
+                        start   = ret.start,
+                        finish  = ret.start + #'return',
+                        message = lang.script('DIAG_MISSING_RETURN_VALUE', {
+                            min  = min,
+                            rmax = rmax,
+                        }),
+                    }
+                else
+                    callback {
+                        start   = ret.start,
+                        finish  = ret.start + #'return',
+                        message = lang.script('DIAG_MISSING_RETURN_VALUE', {
+                            min  = min,
+                            rmin = rmin,
+                            rmax = rmax,
+                        }),
+                    }
+                end
+            end
+        end
+    end)
+end
diff --git a/script/parser/guide.lua b/script/parser/guide.lua
index 56239fb1..a91a6f68 100644
--- a/script/parser/guide.lua
+++ b/script/parser/guide.lua
@@ -12,7 +12,7 @@ local type         = type
 ---@field tag                   string
 ---@field args                  { [integer]: parser.object, start: integer, finish: integer }
 ---@field locals                parser.object[]
----@field returns               parser.object[]
+---@field returns?              parser.object[]
 ---@field exps                  parser.object[]
 ---@field keys                  parser.object[]
 ---@field uri                   uri
diff --git a/script/proto/diagnostic.lua b/script/proto/diagnostic.lua
index 59f33693..5972150c 100644
--- a/script/proto/diagnostic.lua
+++ b/script/proto/diagnostic.lua
@@ -58,6 +58,7 @@ m.register {
     'unbalanced-assignments',
     'redundant-parameter',
     'missing-parameter',
+    'missing-return-value',
 } {
     group    = 'unbalanced',
     severity = 'Warning',
diff --git a/script/vm/function.lua b/script/vm/function.lua
index f992845f..8e3662e2 100644
--- a/script/vm/function.lua
+++ b/script/vm/function.lua
@@ -86,24 +86,15 @@ end
 function vm.countReturnsOfFunction(func, mark)
     if func.type == 'function' then
         local min, max
-        if func.returns then
-            for _, ret in ipairs(func.returns) do
-                local rmin, rmax = vm.countList(ret, mark)
-                if not min or rmin < min then
-                    min = rmin
-                end
-                if not max or rmax > max then
-                    max = rmax
-                end
-            end
-        end
+        local hasDocReturn
         if func.bindDocs then
             local lastReturn
             local n = 0
             local dmin, dmax
             for _, doc in ipairs(func.bindDocs) do
                 if doc.type == 'doc.return' then
-                    for _, ret in ipairs(doc) do
+                    hasDocReturn = true
+                    for _, ret in ipairs(doc.returns) do
                         n = n + 1
                         lastReturn = ret
                         dmax = n
@@ -128,6 +119,17 @@ function vm.countReturnsOfFunction(func, mark)
                 max = dmax
             end
         end
+        if not hasDocReturn and func.returns then
+            for _, ret in ipairs(func.returns) do
+                local rmin, rmax = vm.countList(ret, mark)
+                if not min or rmin < min then
+                    min = rmin
+                end
+                if not max or rmax > max then
+                    max = rmax
+                end
+            end
+        end
         return min or 0, max or math.huge
     end
     if func.type == 'doc.type.function' then