This feature is marked as third degree (³), ie.: an innovative feature that’s very rare in other editors, because I’ve haven’t seen anything like this, ie. eg.: no Vim plugin exists that allows to complete from TAGS file.

Completing The Tags

It’s now possible to complete not only from buffer’s words, but also from symbols in a CTags index file (which is named “TAGS” and is placed in project’s root) – e.g.: for an index that covers /usr/include/glib-2.0, you could complete all GLib functions and types, like so:

Regular completion is bound to Alt-/ by default, while the TAGS completion is Shift-Tab.

This feature allows to have an IDE-like experience – by easy completing of all libraries’ and project’s own functions and types.

Note, that by limiting the completion candidates to project’s symbols a new and robust, and also a very well responsive completion mechanism has been set up.

Hint: Complete Library Symbols

To have not only the source of the project, but also headers of a library used by it indexed by CTags. you could simply link its includes into project’s root, like so (an example):

Then also a ctags invocation with –c-kinds=+p option used is being needed too, so that also function declarations (i.e.: not only definitions) are being indexed, too. Here’s an example Makefile rule/target that executes such a ctags command – after copying, issue make tags-emacs to run it:

tags-emacs:
    @if type ctags >/dev/null 2>&1; then \
        if ctags --version | grep >/dev/null 2>&1 "Universal Ctags"; then \
            ctags -e -R --languages=C --langmap=C:.h.c --c-kinds=+px \
                    --extras=-{anonymous} --extras=+r \
                    --fields=+S --fields-c=+{macrodef} \
                    --pattern-length-limit=250; \
        else \
            ctags -e -R --languages=C --langmap=C:.h.c --c-kinds=+px \
                    --fields=+S .; \
        fi; \
        printf "Created the Emacs \`TAGS\` file.\\n"; \
    else \
       printf 'Error: Missing Ctags (e.g.: either Exuberant or Universal fork) utility first.\n'; \
    fi

The Makefile rule detects if Universal CTags or Exuberant CTags is being installed and runs the appropriate, either a more rich (for Universal …) or more concise (for Exuberant CTags) command. When copying rule’s text into your Makefile (… .am, etc.) make sure that it’s indented with «TABS», not with spaces.