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libexpr: Support structured error classes

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While preparing PRs like #9753, I've had to change error messages in
dozens of code paths. It would be nice if instead of

    EvalError("expected 'boolean' but found '%1%'", showType(v))

we could write

    TypeError(v, "boolean")

or similar. Then, changing the error message could be a mechanical
refactor with the compiler pointing out places the constructor needs to
be changed, rather than the error-prone process of grepping through the
codebase. Structured errors would also help prevent the "same" error
from having multiple slightly different messages, and could be a first
step towards error codes / an error index.

This PR reworks the exception infrastructure in `libexpr` to
support exception types with different constructor signatures than
`BaseError`. Actually refactoring the exceptions to use structured data
will come in a future PR (this one is big enough already, as it has to
touch every exception in `libexpr`).

The core design is in `eval-error.hh`. Generally, errors like this:

    state.error("'%s' is not a string", getAttrPathStr())
      .debugThrow<TypeError>()

are transformed like this:

    state.error<TypeError>("'%s' is not a string", getAttrPathStr())
      .debugThrow()

The type annotation has moved from `ErrorBuilder::debugThrow` to
`EvalState::error`.
This commit is contained in:
Rebecca Turner 2024-01-22 17:08:29 -08:00
parent c62c21e29a
commit c6a89c1a16
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40 changed files with 653 additions and 545 deletions
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4
tests/functional/fetchGit.sh
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@ -67,7 +67,7 @@ path2=$(nix eval --raw --expr "(builtins.fetchGit { url = file://$repo; rev = \"
[[ $(nix eval --raw --expr "builtins.readFile (fetchGit { url = file://$repo; rev = \"$rev2\"; } + \"/hello\")") = world ]]
# But without a hash, it fails
expectStderr 1 nix eval --expr 'builtins.fetchGit "file:///foo"' | grepQuiet "'fetchGit' requires a locked input"
expectStderr 1 nix eval --expr 'builtins.fetchGit "file:///foo"' | grepQuiet "fetchGit requires a locked input"
# Fetch again. This should be cached.
mv $repo ${repo}-tmp
@ -208,7 +208,7 @@ path6=$(nix eval --impure --raw --expr "(builtins.fetchTree { type = \"git\"; ur
[[ $path3 = $path6 ]]
[[ $(nix eval --impure --expr "(builtins.fetchTree { type = \"git\"; url = \"file://$TEST_ROOT/shallow\"; ref = \"dev\"; shallow = true; }).revCount or 123") == 123 ]]
expectStderr 1 nix eval --expr 'builtins.fetchTree { type = "git"; url = "file:///foo"; }' | grepQuiet "'fetchTree' requires a locked input"
expectStderr 1 nix eval --expr 'builtins.fetchTree { type = "git"; url = "file:///foo"; }' | grepQuiet "fetchTree requires a locked input"
# Explicit ref = "HEAD" should work, and produce the same outPath as without ref
path7=$(nix eval --impure --raw --expr "(builtins.fetchGit { url = \"file://$repo\"; ref = \"HEAD\"; }).outPath")