Module alias_input_frames 

alias_input_frames submodule — per-thread record of popped alias input-stack frames, restoring the reachability C’s manually-indexed instack gives input_hasalias. Per-thread record of alias input-stack frames that have already been popped.

zshrs-original infrastructure — no Src/*.c counterpart. It exists because zshrs’s input stack is a Vec and C’s is a manually-indexed array.

Src/input.c:831 input_hasalias() answers “is the text currently being lexed coming out of an alias expansion, and if so which alias?” It does that by walking DOWN instack from instacktop while the flags carry INP_CONT, remembering every frame that has an alias set (Src/input.c:837-846). Src/parse.c:1840 captures the answer at the head of par_simple and Src/parse.c:2061 compares it against a fresh call to decide whether name() { … } is being defined out of an alias body (the ALIAS_FUNC_DEF diagnostic).

The subtlety is that by the time the parser sees the () the alias body has been fully lexed and its frame ALREADY POPPED. C survives that because inpoptop (Src/input.c:757-763) only decrements instacktop — the frame’s storage is untouched — and inungetc walks BACK UP over exhausted alias continuations whenever the lexer pushes the terminator back at a segment start:

if (inbufptr == inbufpush && (inbufflags & (INP_ALCONT|INP_HISTCONT))) {
    do {
        if (instacktop->alias) instacktop->alias->inuse = 1;
        instacktop++;
    } while ((instacktop->flags & (INP_ALCONT|INP_HISTCONT)) && !instacktop->bufleft);
    ...
}

(Src/input.c:587-605)

zshrs’s instack is a Vec<instacks> whose pop() DESTROYS the frame, so that walk-up cannot be reconstructed. This module records the alias name of each frame inpoptop restores that carries INP_ALCONT, in push order, so input_hasalias can report the OUTERMOST one — the same answer C’s downward walk produces for a nested expansion (secondalias → firstalias → body reports secondalias, Test/A02alias.ztst:127-131).

The record is bounded to ONE zshlex call (Src/lex.c:268), which is the whole gettok/exalias chain that produces a single token — so a nested expansion still records every alias in the chain, while a chain that finished during an earlier token cannot answer for a later one. inpoptop additionally clears it when a pop lands on flags without INP_ALCONT.

Functions

clear

Drop the whole record — the alias chain it described has ended.

outermost

The outermost recorded alias name, i.e. what C’s downward instack walk would have settled on.

push

Record the alias name of a just-popped INP_ALCONT frame.