Add debug symbols #87
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code review ack 88d15d3 CI failure looks real (I'll wait til it's green to run my local CI). Super cool concept! |
Introduce a helper method for each step of the analysis. Analyze each call variant in terms of the steps. This refactor makes the code easier to read.
I find it much easier to read hex arrays than long decimal strings.
A Simfony function call f(x) is usually compiled as the following Simplicity expression, where [x] is the compilation of x, and so on. comp [x] [f] However, we can write a different Simplicity target expression that has the same semantics. The input is paired with a false bit. This is piped into an assertion that checks if the bit is false. The assertion always succeeds. comp (pair false [x]) (assertl (drop [f]) CMR) The lower expression is a more convoluted way of writing the upper expression. The benefit of the lower expression is that it includes a CMR that we can use to inject arbitrary data. We use the hash of the position of the call inside the original Simfony source code as CMR. This is the debug symbol. For now, I insert debug symbols into every call that is fallible. Any failure on the Simplicity Bit Machine can be associated with a Simfony call expression via the CMR. Currently, debug symbols are inserted into every compiled program. We don't want programs bloated with debug symbols on the blockchain. It is easy to add a "release" mode next to a "debug" mode to the Simfony compiler. For brevity, I chose to leave this for later. Note that I had to compile unwraps with slightly more combinators in order to fit the shape comp [function args] [function body]. I plan to revert this change in the "release" mod of the Simfony compiler.
We want to use debug symbols to produce helpful error messages on the Bit Machine. The debug symbols cover all cases where the Simplicity target code may fail (assertl, assertr, fail). We want to produce error messages of the following kind: Assertion failed: false Called `unwrap()` on a `None` value Called `unwrap_left()` on a `Right` value: 1 Called `unwrap_right()` on a `Left` value: 1 Some errors display the input value (unwrap_left, unwrap_right); some errors are always the same (assert, unwrap). TrackedCallName includes type information to reconstruct the input value at runtime from the Bit Machine. FallibleCallName includes the reconstructed value. TrackedCall and FallibleCall include the Simfony text of the call expression, so we can print it alongside the error. We might choose to include the span, too, in the future, depending on where we want to go with this design.
Return a plain-old-data type that wraps the Simplicity target code and its debug symbols. When we add a "release" mode to the Simfony compiler, we won't return debug symbols.
dbg!(x) behaves in Simfony like in Rust: It is a NOP that prints its input value as a side effect. The Simfony compiler adds a debug symbol for this purpose. I split FallibleCall from DebugValue in the debug symbol API because FallibleCall is supposed to be used in error messages, while DebugValue is used for logging on the side. I don't want to handle dbg! as a case in an error message, even though dbg! is infallible.
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Fixed CI. Also made sure that |
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Track fallible Simfony expressions via debug symbols that are included in the Simplicity target code (more details are in the commit message).
Add public methods to convert debug symbols into helpful error messages by providing the values that the Bit Machine sees at runtime. Debug symbols cover all failure cases, so the Bit Machine should always be able to display a helpful Simfony error.
Add
dbg!expressions that can be used print their input value at runtime.