array filters should not crash on strings

Official Shopidyf Liquid also can run array filters on strings,
considering them to be one element array.

lib/liquid.lua

@@ -2777,33 +2777,52 @@ function FilterSet:find_filter( filter_name )
        return self.filterset[filter_name]
     end
 end
+
+local function is_iterator(o)
+    local mt = getmetatable(o)
+
+    return mt and mt.__ipairs
+end
+
+local function iterator(o)
+    if type(o) == 'table' or is_iterator(o) then
+        return o
+    else
+        return { o }
+    end
+end
+
 --=== array filter begin
 local function join( a, b)
     -- body
-    return Interpreter:safe_concat(a, b)
+    return Interpreter:safe_concat(iterator(a), b or ' ')
 end
 local function first( a )
     -- body
-    return a[1]
+    return iterator(a)[1]
+end
+local function size( a )
+    -- body
+    return(#iterator(a))
 end
 local function last( a )
     -- body
-    return a[#a]
+    return iterator(a)[size(a)]
 end
 local function concat( a, b)
     -- body
     local temp = {}
-    for i,v in ipairs(a) do
+    for i,v in ipairs(iterator(a)) do
         table.insert(temp, v)
     end
-    for i,v in ipairs(b) do
+    for i,v in ipairs(iterator(b)) do
         table.insert(temp, v)
     end
     return temp
 end
 local function index( a, b)
     -- body
-    return a[(b + 1)]
+    return iterator(a)[(b + 1)]
 end
 local function map( a, map_field)
     -- body
@@ -2816,20 +2835,18 @@ end
 local function reverse( a )
     -- body
     local temp = {}
-    local num = #a
+    local it = iterator(a)
+    local num = size(a)
     for k = num, 1, -1 do
-        table.insert(temp, a[k])
+        table.insert(temp, it[k])
     end
     return temp
 end
-local function size( a )
-    -- body
-    return(#a)
-end
+
 local function sort( a, sort_field)
     -- body
     local t = {}
-    for i,v in ipairs(a) do
+    for i,v in ipairs(iterator(a)) do
         table.insert(t, v)
     end
     if not sort_field then
@@ -2845,7 +2862,7 @@ local function uniq( a )
     -- body
     local t = {}
     local result = {}
-    for i,v in ipairs(a) do
+    for i,v in ipairs(iterator(a)) do
         local k = cjson.encode(v)
         if not t[k] then
             t[k] = true

t/array_filters.t

@@ -7,10 +7,11 @@ plan tests => repeat_each() * (3 * blocks());
 
 my $pwd = cwd();
 
-our $HttpConfig = qq{
+our $HttpConfig = qq|
     lua_package_path "$pwd/lib/?.lua;;;";
     lua_package_cpath "/usr/local/openresty/lualib/?.so;;";
-};
+    init_by_lua_block { Liquid = require 'liquid' }
+|;
 
 
 no_long_string();
@@ -264,3 +265,170 @@ GET /t
 --- no_error_log
 [error]
 
+
+
+=== TEST 11: 'join' filter works on strings
+--- http_config eval: $::HttpConfig
+--- config
+    location /t {
+        content_by_lua_block {
+            ngx.say( Liquid.Template:parse([[
+              {{- str | join: ' - ' -}}
+            ]]):render(Liquid.InterpreterContext:new({ str = "string" })) )
+        }
+    }
+--- request
+GET /t
+--- response_body
+string
+--- no_error_log
+[error]
+
+=== TEST 12: 'first' filter works strings
+--- http_config eval: $::HttpConfig
+--- config
+    location /t {
+        content_by_lua_block {
+            ngx.say( Liquid.Template:parse([[
+              {{- str | first -}}
+            ]]):render(Liquid.InterpreterContext:new({ str = "string" })) )
+        }
+    }
+--- request
+GET /t
+--- response_body
+string
+--- no_error_log
+[error]
+
+
+
+=== TEST 13: 'last' filter works on strings
+--- http_config eval: $::HttpConfig
+--- config
+    location /t {
+        content_by_lua_block {
+            ngx.say( Liquid.Template:parse([[
+                {{- str | last -}}
+            ]]):render( Liquid.InterpreterContext:new({ str = "string" })) )
+        }
+    }
+--- request
+GET /t
+--- response_body
+string
+--- no_error_log
+[error]
+
+=== TEST 14: 'concat' filter works on strings
+--- http_config eval: $::HttpConfig
+--- config
+    location /t {
+        content_by_lua_block {
+            ngx.say( Liquid.Template:parse([[
+              {%- assign a = "string" | concat:(1..3) -%}
+              {%- assign b = "string" | concat: "another" -%}
+              {%- for k in a %} {{k}} {%- endfor -%}
+              {%- for k in b %} {{k}} {%- endfor -%}
+            ]]):render())
+        }
+    }
+--- request
+GET /t
+--- response_body
+ string 1 2 3 string another
+--- no_error_log
+[error]
+
+=== TEST 5: 'index' filter works on strings
+--- http_config eval: $::HttpConfig
+--- config
+    location /t {
+        content_by_lua_block {
+            ngx.say( Liquid.Template:parse([[
+              {{- "string"| index: 0 -}}
+            ]]):render() )
+        }
+    }
+--- request
+GET /t
+--- response_body
+string
+--- no_error_log
+[error]
+
+
+=== TEST 16: 'reverse' filter works on strings
+--- http_config eval: $::HttpConfig
+--- config
+    location /t {
+        content_by_lua_block {
+            ngx.say( Liquid.Template:parse([[
+              {{- "string" | reverse | join -}}
+            ]]):render() )
+        }
+    }
+--- request
+GET /t
+--- response_body
+string
+--- no_error_log
+[error]
+
+
+
+=== TEST 17: 'size' filter works on strings
+--- http_config eval: $::HttpConfig
+--- config
+    location /t {
+        content_by_lua_block {
+            ngx.say( Liquid.Template:parse([[
+              {{- "string" | size -}}
+            ]]):render() )
+        }
+    }
+--- request
+GET /t
+--- response_body
+1
+--- no_error_log
+[error]
+
+
+
+=== TEST 18: 'sort' filter works on strings
+--- http_config eval: $::HttpConfig
+--- config
+    location /t {
+        content_by_lua_block {
+            ngx.say( Liquid.Template:parse([[
+              {{- "string" | sort | join -}}
+            ]]):render() )
+        }
+    }
+--- request
+GET /t
+--- response_body
+string
+
+--- no_error_log
+[error]
+
+
+
+=== TEST 19: 'uniq' filter works on strings
+--- http_config eval: $::HttpConfig
+--- config
+    location /t {
+        content_by_lua_block {
+            ngx.say( Liquid.Template:parse([[
+              {{- "string" | uniq | join -}}
+            ]]):render() )
+        }
+    }
+--- request
+GET /t
+--- response_body
+string
+--- no_error_log
+[error]