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16.8 Which File Defined a Certain Symbol

Function: symbol-file symbol &optional type native-p ¶

This function returns the name of the file that defined symbol. If type is nil, then any kind of definition is acceptable. If type is defun, defvar, or defface, that specifies function definition, variable definition, or face definition only.

The value is normally an absolute file name. It can also be nil, if the definition is not associated with any file. If symbol specifies an autoloaded function, the value can be a relative file name without extension.

If the optional third argument native-p is non-nil, and Emacs was built with native compilation support (see Compilation of Lisp to Native Code), this function will try to find the .eln file that defined symbol, instead of the .elc or .el file. If such a .eln file is found and is not outdated, the function will return its absolute file name; otherwise it will report the name of either the source or the byte-compiled file.

The basis for symbol-file is the data in the variable load-history.

Variable: load-history ¶

The value of this variable is an alist that associates the names of loaded library files with the names of the functions and variables they defined, as well as the features they provided or required.

Each element in this alist describes one loaded library (including libraries that are preloaded at startup). It is a list whose CAR is the absolute file name of the library (a string). The rest of the list elements have these forms:

var

The symbol var was defined as a variable.

(defun . fun)

The function fun was defined. (defun . fun), which represents defining fun as a function.

(defface . face)

The face face was defined.

(require . feature)

The feature feature was required.

(provide . feature)

The feature feature was provided.

(cl-defmethod method specializers)

The named method was defined by using cl-defmethod, with specializers as its specializers.

(define-type . type)

The type type was defined.

The value of load-history may have one element whose CAR is nil. This element describes definitions made with eval-buffer on a buffer that is not visiting a file.

The command eval-region updates load-history, but does so by adding the symbols defined to the element for the file being visited, rather than replacing that element. See Eval.

In addition to load-history, every function keeps track of its own history in the symbol property function-history. The reason why functions are treated specially in this respect is that it is common for functions to be defined in two steps in two different files (typically, one of them is an autoload), so in order to be able to properly unload a file, we need to know more precisely what that file did to the function definition.

The symbol property function-history holds a list of the form (file1 def2 file2 def3 ...), where file1 is the last file that changed the definition and def2 was the definition before file1, set by file2, etc. Logically this list should end with the name of the first file that defined this function, but to save space this last element is usually omitted.