templater: add debugtemplate command This is useful for debugging template parsing. Several tests are ported to this command.

templater: expand list of parsed templates to template node This patch eliminates a nested data structure other than the parsed tree. ('template', [(op, data), ..]) -> ('template', (op, data), ..) New expanded tree can be processed by common parser functions. This change will help implementing template aliases. Because a (template ..) node should have at least one child node, an empty template (template []) is mapped to (string ''). Also a trivial string (template [(string ..)]) node is unwrapped to (string ..) at parsing phase, instead of compiling phase.

templater: relax type of mapped template Now compiled template fragments are packed into a generic type, (func, data), a string can be a valid template. This change allows us to unwrap a trivial string node. See the next patch for details.

templater: lift parsed and compiled templates to generic data types Before this patch, parsed and compiled templates were kept as lists. That was inconvenient for applying transformation such as alias expansion. This patch changes the types of the outermost objects as follows: stage old new -------- -------------- ------------------------------ parsed [(op, ..)] ('template', [(op, ..)]) compiled [(func, data)] (runtemplate, [(func, data)]) New templater.parse() function has the same signature as revset.parse() and fileset.parse().