Pass back explicit errors in load_rules()

Instead of relying on lua errors to pass back parse errors, pass back an
explicit true + required engine version or false + error message.

Also clean up the error message to display info + context on the
error. When the error related to yaml parsing, use the row number passed
back in lyaml's error string to print the specific line with the error.

When parsing rules/macros/lists, print the object being parsed alongside
the error.

Signed-off-by: Mark Stemm <mark.stemm@gmail.com>

userspace/engine/lua/compiler.lua

@@ -62,12 +62,12 @@ function expand_macros(ast, defs, changed)
    elseif ast.type == "Filter" then
       if (ast.value.type == "Macro") then
          if (defs[ast.value.value] == nil) then
-            error("Undefined macro '".. ast.value.value .. "' used in filter.")
+	    return false, "Undefined macro '".. ast.value.value .. "' used in filter."
          end
 	 defs[ast.value.value].used = true
          ast.value = copy_ast_obj(defs[ast.value.value].ast)
          changed = true
-	 return changed
+	 return true, changed
       end
       return expand_macros(ast.value, defs, changed)
 
@@ -75,7 +75,7 @@ function expand_macros(ast, defs, changed)
 
       if (ast.left.type == "Macro") then
          if (defs[ast.left.value] == nil) then
-            error("Undefined macro '".. ast.left.value .. "' used in filter.")
+	    return false, "Undefined macro '".. ast.left.value .. "' used in filter."
          end
 	 defs[ast.left.value].used = true
          ast.left = copy_ast_obj(defs[ast.left.value].ast)
@@ -84,21 +84,27 @@ function expand_macros(ast, defs, changed)
 
       if (ast.right.type == "Macro") then
          if (defs[ast.right.value] == nil) then
-            error("Undefined macro ".. ast.right.value .. " used in filter.")
+	    return false, "Undefined macro ".. ast.right.value .. " used in filter."
          end
 	 defs[ast.right.value].used = true
          ast.right = copy_ast_obj(defs[ast.right.value].ast)
          changed = true
       end
 
-      local changed_left = expand_macros(ast.left, defs, false)
-      local changed_right = expand_macros(ast.right, defs, false)
-      return changed or changed_left or changed_right
+      local status, changed_left = expand_macros(ast.left, defs, false)
+      if status == false then
+	 return false, changed_left
+      end
+      local status, changed_right = expand_macros(ast.right, defs, false)
+      if status == false then
+	 return false, changed_right
+      end
+      return true, changed or changed_left or changed_right
 
    elseif ast.type == "UnaryBoolOp" then
       if (ast.argument.type == "Macro") then
          if (defs[ast.argument.value] == nil) then
-            error("Undefined macro ".. ast.argument.value .. " used in filter.")
+	    return false, "Undefined macro ".. ast.argument.value .. " used in filter."
          end
 	 defs[ast.argument.value].used = true
          ast.argument = copy_ast_obj(defs[ast.argument.value].ast)
@@ -106,7 +112,7 @@ function expand_macros(ast, defs, changed)
       end
       return expand_macros(ast.argument, defs, changed)
    end
-   return changed
+   return true, changed
 end
 
 function get_macros(ast, set)
@@ -195,7 +201,7 @@ function compiler.compile_macro(line, macro_defs, list_defs)
 
    if (error_msg) then
       msg = "Compilation error when compiling \""..line.."\": ".. error_msg
-      error(msg)
+      return false, msg
    end
 
    -- Simply as a validation step, try to expand all macros in this
@@ -206,14 +212,18 @@ function compiler.compile_macro(line, macro_defs, list_defs)
    if (ast.type == "Rule") then
       -- Line is a filter, so expand macro references
       repeat
-	 expanded  = expand_macros(ast_copy, macro_defs, false)
+	 status, expanded = expand_macros(ast_copy, macro_defs, false)
+	 if status == false then
+	    msg = "Compilation error when compiling \""..line.."\": ".. expanded
+	    return false, msg
+	 end
       until expanded == false
 
    else
-      error("Unexpected top-level AST type: "..ast.type)
+      return false, "Unexpected top-level AST type: "..ast.type
    end
 
-   return ast
+   return true, ast
 end
 
 --[[
@@ -227,22 +237,25 @@ function compiler.compile_filter(name, source, macro_defs, list_defs)
 
    if (error_msg) then
       msg = "Compilation error when compiling \""..source.."\": "..error_msg
-      error(msg)
+      return false, msg
    end
 
    if (ast.type == "Rule") then
       -- Line is a filter, so expand macro references
       repeat
-	 expanded  = expand_macros(ast, macro_defs, false)
+	 status, expanded  = expand_macros(ast, macro_defs, false)
+	 if status == false then
+	    return false, expanded
+	 end
       until expanded == false
 
    else
-      error("Unexpected top-level AST type: "..ast.type)
+      return false, "Unexpected top-level AST type: "..ast.type
    end
 
    filters = get_filters(ast)
 
-   return ast, filters
+   return true, ast, filters
 end