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libcmd/repl: allow :st argument to be relative to current stack index

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See [lix-project/lix#1156], but basically currently the `:st <n>`
debugger command doesn't allow any negative indices, and putting a plus
sign in front of the arg doesn't change anything; thus, we can exploit
that "design space" to allow users to move between different stack
frames easily, by simply prepending their arg with a +/- sign.

The actual behavior is little more nuanced when you account for errors:
as suggested by @pennae (thanks! :), when the user inputs an offset that
would result in an invalid frame index, the debugger instead clamps it
to the closest bound (i.e. 0 for negative offsets, $maxFrame for
positive ones) and just prints a warning.

Fixes #1156

[lix-project/lix#1156]: https://git.lix.systems/lix-project/lix/issues/1156

Change-Id: I02a0cdb6aaebbdb0515308880a3bf9c0d2fcd25e
This commit is contained in:
blokyk
2026-03-20 18:22:24 +01:00
parent 774f957599
commit daadfed9ae
6 changed files with 217 additions and 37 deletions
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tests/functional/repl_characterization/data/stacktrace_oob.test
+45 -12
View File
@@ -40,21 +40,11 @@ frames from 0 up to 4 work fine
Env level 2
abort baseNameOf break builtins derivation derivationStrict dirOf false fetchGit fetchMercurial fetchTarball fetchTree fromTOML import isNull map null placeholder removeAttrs scopedImport throw toString true
negative frames print an error
nix-repl> :st -1
error: stack index must be between 0 and 4, but was -1
nix-repl> :st -100
error: stack index must be between 0 and 4, but was -100
positives frames out of bounds also print an error
absolute frames out of bounds print an error
nix-repl> :st 5
error: stack index must be between 0 and 4, but was 5
nix-repl> :st 100
error: stack index must be between 0 and 4, but was 100
argument-less :st is still at the same after oob
argument-less :st is still at the same after absolute oob
nix-repl> :st
4: while evaluating a 'let' expression
@@ -72,6 +62,49 @@ argument-less :st is still at the same after oob
Env level 2
abort baseNameOf break builtins derivation derivationStrict dirOf false fetchGit fetchMercurial fetchTarball fetchTree fromTOML import isNull map null placeholder removeAttrs scopedImport throw toString true
positive relative frames oob clamp to upper bound and print a warning
nix-repl> :st +5
4: while evaluating a 'let' expression
«string»:1:1
1| let f = _: throw "x_x"; x = f 5; in x
| ^
Env level 0
static: f x
Env level 1
static:
Env level 2
abort baseNameOf break builtins derivation derivationStrict dirOf false fetchGit fetchMercurial fetchTarball fetchTree fromTOML import isNull map null placeholder removeAttrs scopedImport throw toString true
warning: stopped at stack frame 4, cannot go any higher
negative relative frames oob clamp to lower bound and print a warning
nix-repl> :st -5
0: error: x_x
«string»:1:12
1| let f = _: throw "x_x"; x = f 5; in x
| ^
Env level 0
static: _
Env level 1
static: f x
Env level 2
static:
Env level 3
abort baseNameOf break builtins derivation derivationStrict dirOf false fetchGit fetchMercurial fetchTarball fetchTree fromTOML import isNull map null placeholder removeAttrs scopedImport throw toString true
warning: stopped at stack frame 0, cannot go any deeper
quit
nix-repl> :quit
error: x_x