escape table keys that map to lua keywords (#59)

inspect.lua

@@ -87,8 +87,35 @@ local function escape(str)
    "%c", shortControlCharEscapes))
 end
 
+local luaKeywords = {
+   ['and'] = true,
+   ['break'] = true,
+   ['do'] = true,
+   ['else'] = true,
+   ['elseif'] = true,
+   ['end'] = true,
+   ['false'] = true,
+   ['for'] = true,
+   ['function'] = true,
+   ['goto'] = true,
+   ['if'] = true,
+   ['in'] = true,
+   ['local'] = true,
+   ['nil'] = true,
+   ['not'] = true,
+   ['or'] = true,
+   ['repeat'] = true,
+   ['return'] = true,
+   ['then'] = true,
+   ['true'] = true,
+   ['until'] = true,
+   ['while'] = true,
+}
+
 local function isIdentifier(str)
-   return type(str) == "string" and not not str:match("^[_%a][_%a%d]*$")
+   return type(str) == "string" and
+   not not str:match("^[_%a][_%a%d]*$") and
+   not luaKeywords[str]
 end
 
 local flr = math.floor

inspect.tl

@@ -87,8 +87,35 @@ local function escape(str: string): string
       "%c", shortControlCharEscapes))
 end
 
+local luaKeywords: {string:boolean} = {
+  ['and'] = true,
+  ['break'] = true,
+  ['do'] = true,
+  ['else'] = true,
+  ['elseif'] = true,
+  ['end'] = true,
+  ['false'] = true,
+  ['for'] = true,
+  ['function'] = true,
+  ['goto'] = true,
+  ['if'] = true,
+  ['in'] = true,
+  ['local'] = true,
+  ['nil'] = true,
+  ['not'] = true,
+  ['or'] = true,
+  ['repeat'] = true,
+  ['return'] = true,
+  ['then'] = true,
+  ['true'] = true,
+  ['until'] = true,
+  ['while'] = true,
+}
+
 local function isIdentifier(str: any): boolean
-   return str is string and not not str:match("^[_%a][_%a%d]*$")
+   return str is string
+    and not not str:match("^[_%a][_%a%d]*$")
+    and not luaKeywords[str]
 end
 
 local flr = math.floor

spec/inspect_spec.lua

@@ -111,6 +111,13 @@ describe( 'inspect', function()
       end)
     end
 
+    it('escapes string keys that are not valid identifiers', function()
+      assert.equals(unindent([[{
+        ["if"] = true,
+        ["key with spaces"] = true
+      }]]), inspect({['if'] = true, ['key with spaces'] = true}))
+    end)
+
     it('works with simple dictionary tables', function()
       assert.equals("{\n  a = 1,\n  b = 2\n}", inspect({a = 1, b = 2}))
     end)