Fix an error with LazyVars (FAForever#3725)

A lazy value could not be `false`.

lua/lazyvar.lua

@@ -0,0 +1,119 @@
+--
+-- LazyVar module
+--
+
+
+local EvalContext = nil
+
+local LazyVarMetaTable = { }
+
+LazyVarMetaTable.__index = LazyVarMetaTable
+
+local WeakKeyMeta = { __mode = 'k' }
+
+-- Set this true to get tracebacks in error messages. It slows down lazyvars a lot,
+-- so don't use except when debugging.
+ExtendedErrorMessages = false
+
+function LazyVarMetaTable:__call()
+    if self.compute then
+        if self.busy then
+            error("circular dependency in lazy evaluation for variable " .. (self.trace or ''), 2)
+        end
+        self.busy = true
+        local u
+        for u in self.uses do
+            u.used_by[self] = nil
+        end
+        self.uses = {}
+        local oldContext = EvalContext
+        EvalContext = self
+        local okay, value = pcall(self.compute)
+        EvalContext = oldContext
+        self.busy = nil
+        if okay then
+            self[1] = value
+        else
+            error("error evaluating lazy variable: " .. value .. "\nStack trace from definition: " .. (self.trace or '') .. '\n', 2)
+        end
+    end
+    if EvalContext then
+        EvalContext.uses[self] = true
+        self.used_by[EvalContext] = true
+    end
+    return self[1]
+end
+
+function LazyVarMetaTable:SetDirty(onDirtyList)
+    if self[1]~=nil then
+        if self.OnDirty then
+            table.insert(onDirtyList, self)
+        end
+        self[1] = nil
+        local u for u in self.used_by do 
+            u:SetDirty(onDirtyList)
+        end
+    end
+end 
+
+function LazyVarMetaTable:SetFunction(func)
+    local dirtyList = {}
+    self:SetDirty(dirtyList)
+    self.compute = func
+    if ExtendedErrorMessages then
+        self.trace = debug.traceback('set from:')
+    else
+        self.trace = '[Set lazyvar.ExtendedErrorMessages for extra trace info]'
+    end
+
+    for i,v in ipairs(dirtyList) do
+        v:OnDirty()
+    end
+end
+
+function LazyVarMetaTable:SetValue(value)
+    local dirtyList = {}
+    self:SetDirty(dirtyList)
+    self.compute = nil
+    self.trace = nil
+    self[1] = value
+    -- Now remove us from the used_by lists for any lazy vars we used to use.
+    for u in self.uses do
+        u.used_by[self] = nil
+    end
+    self.uses = {}
+    for i,v in ipairs(dirtyList) do
+        v:OnDirty()
+    end
+end
+
+function LazyVarMetaTable:Set(v)
+    if v == nil then
+        error("You are attempting to set a LazyVar's evaluation function to nil, don't do that!")    
+    end
+    if iscallable(v) then
+        self:SetFunction(v)
+    else
+        self:SetValue(v)
+    end
+end
+
+function LazyVarMetaTable:Destroy()
+    self.OnDirty = nil
+    self.compute = nil
+    self.value = nil
+end
+
+function Create(initial)
+    result = {&1&4}
+    setmetatable(result, LazyVarMetaTable)
+    if initial == nil then 
+        result[1] = 0
+    else
+        result[1] = initial
+    end
+    result.used_by = {}
+    setmetatable(result.used_by, WeakKeyMeta)
+    result.uses = {}
+    return result
+end

run_lua_tests.sh

@@ -20,8 +20,12 @@ check_file() {
 # Some files have spaces in their name so we use this syntax to make sure the
 # output from `find` is split by line.
 while read file; do
-  check_file "$file"
-  (( files_checked++ ))
+
+  # file contains table pre-allocation synax ( {&1&4} ) that is not supported at the moment
+  if [ "$file" != "./lua/lazyvar.lua" ]; then 
+    check_file "$file"
+    (( files_checked++ ))
+  fi
 done < <(find . -type d \( -path ./testmaps -o -path ./engine \) -prune -false -o -name '*.lua' -o -name '*.bp')
 
 echo "Checked $files_checked files"