# Debugging Revise

## Handling errors

Revise attempts to make error reports mimic Julia's own stacktraces, and as a consequence it has to prevent stacktraces from containing lots of lines pointing to Revise's own code. If you're trying to debug a Revise error, you'd probably prefer to see the entire stacktrace. You can uncomment the obvious commented-out line in Revise.trim_toplevel!.

## The logging framework

If Revise isn't behaving the way you expect it to, it can be useful to examine the decisions it made. Revise supports Julia's Logging framework and can optionally record its decisions in a format suitable for later inspection. What follows is a simple series of steps you can use to turn on logging, capture messages, and then submit them with a bug report. Alternatively, more advanced developers may want to examine the logs themselves to determine the source of Revise's error, and for such users a few tips about interpreting the log messages are also provided below.

### Turning on logging

Currently, the best way to turn on logging is within a running Julia session:

julia> rlogger = Revise.debug_logger()
Revise.ReviseLogger(Revise.LogRecord[], Debug)

You'll use rlogger at the end to retrieve the logs.

Now carry out the series of julia commands and code edits that reproduces the problem.

### Capturing the logs and submitting them with your bug report

Once all the revisions have been triggered and the mistake has been reproduced, it's time to capture the logs. To capture all the logs, use

julia> using Base.CoreLogging: Debug

julia> logs = filter(r->r.level==Debug, rlogger.logs);

You can capture just the changes that Revise made to running code with

julia> logs = Revise.actions(rlogger)

You can either let these print to the console and copy/paste the text output into the issue, or if they are extensive you can save logs to a file:

open("/tmp/revise.logs", "w") do io
println(io, log)
end
end

Then you can upload the logs somewhere (e.g., https://gist.github.com/) and link the url in your bug report. To assist in the resolution of the bug, please also specify additional relevant information such as the name of the function that was misbehaving after revision and/or any error messages that your received.

### Logging by default

If you suspect a bug in Revise but have difficulty isolating it, you can include the lines

    # Turn on logging
Revise.debug_logger()

within the Revise block of your ~/.julia/config/startup.jl file. This will ensure that you always log Revise's actions. Then carry out your normal Julia development. If a Revise-related problem arises, executing these lines

rlogger = Revise.debug_logger()
using Base.CoreLogging: Debug
logs = filter(r->r.level==Debug, rlogger.logs)
open("/tmp/revise.logs", "w") do io
println(io, log)
end
end

within the same session will generate the /tmp/revise.logs file that you can submit with your bug report. (What makes this possible is that a second call to Revise.debug_logger() returns the same logger object created by the first call–it is not necessary to hold on to rlogger.)

### The structure of the logs

For those who want to do a little investigating on their own, it may be helpful to know that Revise's core decisions are captured in the group called "Action," and they come in three flavors:

• log entries with message "Eval" signify a call to eval; for these events, keyword :deltainfo has value (mod, expr) where mod is the module of evaluation and expr is a Revise.RelocatableExpr containing the expression that was evaluated.
• log entries with message "DeleteMethod" signify a method deletion; for these events, keyword :deltainfo has value (sigt, methsummary) where sigt is the signature of the method that Revise intended to delete and methsummary is a MethodSummary of the method that Revise actually found to delete.
• log entries with message "LineOffset" correspond to updates to Revise's own internal estimates of how far a given method has become displaced from the line number it occupied when it was last evaluated. For these events, :deltainfo has value (sigt, newlineno, oldoffset=>newoffset).

If you're debugging mistakes in method creation/deletion, the "LineOffset" events may be distracting; by default Revise.actions excludes these events.

Note that Revise records the time of each revision, which can sometimes be useful in determining which revisions occur in conjunction with which user actions. If you want to make use of this, it can be handy to capture the start time with tstart = time() before commencing on a session.

See Revise.debug_logger for information on groups besides "Action."

### A complete debugging demo

From within Revise's test/ directory, try the following:

julia> rlogger = Revise.debug_logger();

shell> cp revisetest.jl /tmp/

julia> includet("/tmp/revisetest.jl")

julia> ReviseTest.cube(3)
81

shell> cp revisetest_revised.jl /tmp/revisetest.jl

julia> ReviseTest.cube(3)
27

julia> rlogger.logs
julia> rlogger.logs
9-element Array{Revise.LogRecord,1}:
Revise.LogRecord(Debug, DeleteMethod, Action, Revise_4ac0f476, "/home/tim/.julia/dev/Revise/src/Revise.jl", 226, (time=1.557996459055345e9, deltainfo=(Tuple{typeof(Main.ReviseTest.cube),Any}, MethodSummary(:cube, :ReviseTest, Symbol("/tmp/revisetest.jl"), 7, Tuple{typeof(Main.ReviseTest.cube),Any}))))
Revise.LogRecord(Debug, DeleteMethod, Action, Revise_4ac0f476, "/home/tim/.julia/dev/Revise/src/Revise.jl", 226, (time=1.557996459167895e9, deltainfo=(Tuple{typeof(Main.ReviseTest.Internal.mult3),Any}, MethodSummary(:mult3, :Internal, Symbol("/tmp/revisetest.jl"), 12, Tuple{typeof(Main.ReviseTest.Internal.mult3),Any}))))
Revise.LogRecord(Debug, DeleteMethod, Action, Revise_4ac0f476, "/home/tim/.julia/dev/Revise/src/Revise.jl", 226, (time=1.557996459167956e9, deltainfo=(Tuple{typeof(Main.ReviseTest.Internal.mult4),Any}, MethodSummary(:mult4, :Internal, Symbol("/tmp/revisetest.jl"), 13, Tuple{typeof(Main.ReviseTest.Internal.mult4),Any}))))
Revise.LogRecord(Debug, Eval, Action, Revise_9147188b, "/home/tim/.julia/dev/Revise/src/Revise.jl", 276, (time=1.557996459259605e9, deltainfo=(Main.ReviseTest, :(cube(x) = begin
#= /tmp/revisetest.jl:7 =#
x ^ 3
end))))
Revise.LogRecord(Debug, Eval, Action, Revise_9147188b, "/home/tim/.julia/dev/Revise/src/Revise.jl", 276, (time=1.557996459330512e9, deltainfo=(Main.ReviseTest, :(fourth(x) = begin
#= /tmp/revisetest.jl:9 =#
x ^ 4
end))))
Revise.LogRecord(Debug, LineOffset, Action, Revise_fb38a7f7, "/home/tim/.julia/dev/Revise/src/Revise.jl", 296, (time=1.557996459331061e9, deltainfo=(Any[Tuple{typeof(mult2),Any}], :(#= /tmp/revisetest.jl:11 =#) => :(#= /tmp/revisetest.jl:13 =#))))
Revise.LogRecord(Debug, Eval, Action, Revise_9147188b, "/home/tim/.julia/dev/Revise/src/Revise.jl", 276, (time=1.557996459391182e9, deltainfo=(Main.ReviseTest.Internal, :(mult3(x) = begin
#= /tmp/revisetest.jl:14 =#
3x
end))))
Revise.LogRecord(Debug, LineOffset, Action, Revise_fb38a7f7, "/home/tim/.julia/dev/Revise/src/Revise.jl", 296, (time=1.557996459391642e9, deltainfo=(Any[Tuple{typeof(unchanged),Any}], :(#= /tmp/revisetest.jl:18 =#) => :(#= /tmp/revisetest.jl:19 =#))))
Revise.LogRecord(Debug, LineOffset, Action, Revise_fb38a7f7, "/home/tim/.julia/dev/Revise/src/Revise.jl", 296, (time=1.557996459391695e9, deltainfo=(Any[Tuple{typeof(unchanged2),Any}], :(#= /tmp/revisetest.jl:20 =#) => :(#= /tmp/revisetest.jl:21 =#))))

You can see that Revise started by deleting three methods, followed by evaluating three new versions of those methods. Interspersed are various changes to the line numbering.

In rare cases it might be helpful to independently record the sequence of edits to the file. You can make copies cp editedfile.jl > /tmp/version1.jl, edit code, cp editedfile.jl > /tmp/version2.jl, etc. diff version1.jl version2.jl can be used to capture a compact summary of the changes and pasted into the bug report.

## Debugging problems with paths

During certain types of usage you might receive messages like

Warning: /some/system/path/stdlib/v1.0/SHA/src is not an existing directory, Revise is not watching

Unless you've just deleted that directory, this indicates that some of Revise's functionality is broken.

In the majority of cases, failures come down to Revise having trouble locating source code on your drive. This problem should be fixable, because Revise includes functionality to update its links to source files, as long as it knows what to do.

One of the best approaches is to run Revise's own tests via pkg> test Revise. Here are some possible test warnings and errors, and steps you might take to fix them:

• Base & stdlib file paths: Test Failed at /some/path... Expression: isfile(Revise.basesrccache) This failure is quite serious, and indicates that you will be unable to access code in Base. To fix this, look for a file called "base.cache" somewhere in your Julia install or build directory (for the author, it is at /home/tim/src/julia-1.0/usr/share/julia/base.cache). Now compare this with the value of Revise.basesrccache. (If you're getting this failure, presumably they are different.) An important "top level" directory is Sys.BINDIR; if they differ already at this level, consider adding a symbolic link from the location pointed at by Sys.BINDIR to the corresponding top-level directory in your actual Julia installation. You'll know you've succeeded in specifying it correctly when, after restarting Julia, Revise.basesrccache points to the correct file and Revise.juliadir points to the directory that contains base/. If this workaround is not possible or does not succeed, please file an issue with a description of why you can't use it and/or
• details from versioninfo and information about how you obtained your Julia installation;
• the values of Revise.basesrccache and Revise.juliadir, and the actual paths to base.cache and the directory containing the running Julia's base/;
• what you attempted when trying to fix the problem;
• if possible, your best understanding of why this failed to fix it.
• skipping Core.Compiler tests due to lack of git repo: this likely indicates that you downloaded a Julia binary rather than building Julia from source. While Revise should be able to access the code in Base and standard libraries, at the current time it is not possible for Revise to access julia's Core.Compiler module unless you clone Julia's repository and build it from source.
• skipping git tests because Revise is not under development: this warning should be harmless. Revise has built-in functionality for extracting source code using git, and it uses itself (i.e., its own git repository) for testing purposes. These tests run only if you have checked out Revise for development (pkg> dev Revise) or on the continuous integration servers (Travis and Appveyor).