4d7818a76a
This commit enhances AstGen to introduce a form of error resilience which allows valid ZIR to be emitted even when AstGen errors occur. When a non-fatal AstGen error (e.g. `appendErrorNode`) occurs, ZIR generation is not affected; the error is added to `astgen.errors` and ultimately to the errors stored in `extra`, but that doesn't stop us getting valid ZIR. Fatal AstGen errors (e.g. `failNode`) are a bit trickier. These errors return `error.AnalysisFail`, which is propagated up the stack. In theory, any parent expression can catch this error and handle it, continuing ZIR generation whilst throwing away whatever was lost. For now, we only do this in one place: when creating declarations. If a call to `fnDecl`, `comptimeDecl`, `globalVarDecl`, etc, returns `error.AnalysisFail`, the `declaration` instruction is still created, but its body simply contains the new `extended(astgen_error())` instruction, which instructs Sema to terminate semantic analysis with a transitive error. This means that a fatal AstGen error causes the innermost declaration containing the error to fail, but the rest of the file remains intact. If a source file contains parse errors, or an `error.AnalysisFail` happens when lowering the top-level struct (e.g. there is an error in one of its fields, or a name has multiple declarations), then lowering for the entire file fails. Alongside the existing `Zir.hasCompileErrors` query, this commit introduces `Zir.loweringFailed`, which returns `true` only in this case. The end result here is that files with AstGen failures will almost always still emit valid ZIR, and hence can undergo semantic analysis on the parts of the file which are (from AstGen's perspective) valid. This is a noteworthy improvement to UX, but the main motivation here is actually incremental compilation. Previously, AstGen failures caused lots of semantic analysis work to be thrown out, because all `AnalUnit`s in the file required re-analysis so as to trigger necessary transitive failures and remove stored compile errors which would no longer make sense (because a fresh compilation of this code would not emit those errors, as the units those errors applied to would fail sooner due to referencing a failed file). Now, this case only applies when a file has severe top-level errors, which is far less common than something like having an unused variable. Lastly, this commit changes a few errors in `AstGen` to become fatal when they were previously non-fatal and vice versa. If there is still a reasonable way to continue AstGen and lower to ZIR after an error, it is non-fatal; otherwise, it is fatal. For instance, `comptime const`, while redundant syntax, has a clear meaning we can lower; on the other hand, using an undeclared identifer has no sane lowering, so must trigger a fatal error.
A general-purpose programming language and toolchain for maintaining robust, optimal, and reusable software.
Documentation
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Building from Source
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Building from Source without LLVM
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Contributing
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One of the best ways you can contribute to Zig is to start using it for an open-source personal project.
This leads to discovering bugs and helps flesh out use cases, which lead to further design iterations of Zig. Importantly, each issue found this way comes with real world motivations, making it straightforward to explain the reasoning behind proposals and feature requests.
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The issue label Contributor Friendly exists to help you find issues that are limited in scope and/or knowledge of Zig internals.
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