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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
No known key found for this signature in database
40 changed files with 653 additions and 545 deletions
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20
tests/unit/libexpr/error_traces.cc
View file

@ -12,33 +12,33 @@ namespace nix {
TEST_F(ErrorTraceTest, TraceBuilder) {
ASSERT_THROW(
state.error("Not much").debugThrow<EvalError>(),
state.error<EvalError>("puppy").debugThrow(),
EvalError
);
ASSERT_THROW(
state.error("Not much").withTrace(noPos, "No more").debugThrow<EvalError>(),
state.error<EvalError>("puppy").withTrace(noPos, "doggy").debugThrow(),
EvalError
);
ASSERT_THROW(
try {
try {
state.error("Not much").withTrace(noPos, "No more").debugThrow<EvalError>();
state.error<EvalError>("puppy").withTrace(noPos, "doggy").debugThrow();
} catch (Error & e) {
e.addTrace(state.positions[noPos], "Something", "");
e.addTrace(state.positions[noPos], "beans", "");
throw;
}
} catch (BaseError & e) {
ASSERT_EQ(PrintToString(e.info().msg),
PrintToString(hintfmt("Not much")));
PrintToString(hintfmt("puppy")));
auto trace = e.info().traces.rbegin();
ASSERT_EQ(e.info().traces.size(), 2);
ASSERT_EQ(PrintToString(trace->hint),
PrintToString(hintfmt("No more")));
PrintToString(hintfmt("doggy")));
trace++;
ASSERT_EQ(PrintToString(trace->hint),
PrintToString(hintfmt("Something")));
PrintToString(hintfmt("beans")));
throw;
}
, EvalError
@ -47,12 +47,12 @@ namespace nix {
TEST_F(ErrorTraceTest, NestedThrows) {
try {
state.error("Not much").withTrace(noPos, "No more").debugThrow<EvalError>();
state.error<EvalError>("puppy").withTrace(noPos, "doggy").debugThrow();
} catch (BaseError & e) {
try {
state.error("Not much more").debugThrow<EvalError>();
state.error<EvalError>("beans").debugThrow();
} catch (Error & e2) {
e.addTrace(state.positions[noPos], "Something", "");
e.addTrace(state.positions[noPos], "beans2", "");
//e2.addTrace(state.positions[noPos], "Something", "");
ASSERT_TRUE(e.info().traces.size() == 2);
ASSERT_TRUE(e2.info().traces.size() == 0);