4945f046c7
In f6d25d7878 (api docs: document that BUG() emits a trace2 error event,
2021-04-13), a link to the plain text version of api-trace2 was added in
`technical/api-error-handling.txt`.
All of our other `link:`s point to the html versions. Do the same here.
Signed-off-by: Todd Zullinger <tmz@pobox.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
104 lines
3.7 KiB
Plaintext
104 lines
3.7 KiB
Plaintext
Error reporting in git
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======================
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`BUG`, `bug`, `die`, `usage`, `error`, and `warning` report errors of
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various kinds.
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- `BUG` is for failed internal assertions that should never happen,
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i.e. a bug in git itself.
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- `bug` (lower-case, not `BUG`) is supposed to be used like `BUG` but
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prints a "BUG" message instead of calling `abort()`.
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+
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A call to `bug()` will then result in a "real" call to the `BUG()`
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function, either explicitly by invoking `BUG_if_bug()` after call(s)
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to `bug()`, or implicitly at `exit()` time where we'll check if we
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encountered any outstanding `bug()` invocations.
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+
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If there were no prior calls to `bug()` before invoking `BUG_if_bug()`
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the latter is a NOOP. The `BUG_if_bug()` function takes the same
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arguments as `BUG()` itself. Calling `BUG_if_bug()` explicitly isn't
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necessary, but ensures that we die as soon as possible.
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+
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If you know you had prior calls to `bug()` then calling `BUG()` itself
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is equivalent to calling `BUG_if_bug()`, the latter being a wrapper
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calling `BUG()` if we've set a flag indicating that we've called
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`bug()`.
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+
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This is for the convenience of APIs who'd like to potentially report
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more than one "bug", such as the optbug() validation in
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parse-options.c.
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- `die` is for fatal application errors. It prints a message to
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the user and exits with status 128.
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- `usage` is for errors in command line usage. After printing its
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message, it exits with status 129. (See also `usage_with_options`
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in the link:api-parse-options.html[parse-options API].)
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- `error` is for non-fatal library errors. It prints a message
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to the user and returns -1 for convenience in signaling the error
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to the caller.
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- `warning` is for reporting situations that probably should not
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occur but which the user (and Git) can continue to work around
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without running into too many problems. Like `error`, it
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returns -1 after reporting the situation to the caller.
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These reports will be logged via the trace2 facility. See the "error"
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event in link:api-trace2.html[trace2 API].
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Customizable error handlers
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---------------------------
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The default behavior of `die` and `error` is to write a message to
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stderr and then exit or return as appropriate. This behavior can be
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overridden using `set_die_routine` and `set_error_routine`. For
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example, "git daemon" uses set_die_routine to write the reason `die`
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was called to syslog before exiting.
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Library errors
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--------------
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Functions return a negative integer on error. Details beyond that
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vary from function to function:
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- Some functions return -1 for all errors. Others return a more
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specific value depending on how the caller might want to react
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to the error.
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- Some functions report the error to stderr with `error`,
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while others leave that for the caller to do.
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- errno is not meaningful on return from most functions (except
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for thin wrappers for system calls).
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Check the function's API documentation to be sure.
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Caller-handled errors
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---------------------
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An increasing number of functions take a parameter 'struct strbuf *err'.
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On error, such functions append a message about what went wrong to the
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'err' strbuf. The message is meant to be complete enough to be passed
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to `die` or `error` as-is. For example:
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if (ref_transaction_commit(transaction, &err))
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die("%s", err.buf);
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The 'err' parameter will be untouched if no error occurred, so multiple
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function calls can be chained:
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t = ref_transaction_begin(&err);
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if (!t ||
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ref_transaction_update(t, "HEAD", ..., &err) ||
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ret_transaction_commit(t, &err))
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die("%s", err.buf);
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The 'err' parameter must be a pointer to a valid strbuf. To silence
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a message, pass a strbuf that is explicitly ignored:
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if (thing_that_can_fail_in_an_ignorable_way(..., &err))
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/* This failure is okay. */
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strbuf_reset(&err);
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