Namespaced functions #639
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Namespaced functions #639
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In the modern Go Modules-based toolchain we can avoid the need to globally install this tool first by running it this way. As a bonus, the toolchain will also install the version of the module we have specified in go.mod, thereby locking us in to a particular version until we intentionally upgrade. The other third-party generator tools we use here aren't written in Go and so we can't do the same for those right now, but maybe we'll find a nicer way to handle those later too.
This introduces a new syntax which allows function names to have namespace prefixes, with the different name parts separated by a double-colon "::" as is common in various other C-derived languages which need to distinguish between scope resolution and attribute/field traversal. Because HCL has separate namespaces for functions and variables, we need to use different punctuation for each to avoid creating parsing ambiguity that could be resolved only with infinite lookahead. We cannot retroactively change the representation of function names to be a slice of names without breaking the existing API, and so we instead adopt a convention of packing the multi-part names into single strings which the parser guarantees will always be a series of valid identifiers separated by the literal "::" sequence. That means that applications will make namespaced functions available in the EvalContext by naming them in a way that matches this convention. This is still a subtle compatibility break for any implementation of the syntax-agnostic HCL API against another syntax, because it may now encounter function names in the function table that are not entirely valid identifiers. However, that's okay in practice because a calling application is always in full control of both which syntaxes it supports and which functions it places in the function table, and so an application using some other syntax can simply avoid using namespaced functions until that syntax is updated to understand the new convention. This initial commit only includes the basic functionality and does not yet update the specification or specification test suite. It also has only minimal unit tests of the parser and evaluator. Before finalizing this in a release we would need to complete that work to make sure everything is consistent and that we have sufficient regression tests for this new capability.
Add a locals blocks to the terraformlike tests, with normal and scoped function calls.
apparentlymart
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Nov 2, 2023
radeksimko
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Nov 3, 2023
dbanck
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This introduces a new syntax which allows function names to have namespace prefixes, with the different name parts separated by a double-colon
::as is common in various other C-derived languages which need to distinguish between scope resolution and attribute/field traversal. (For example: C++, Rust, Ruby, and Perl.)Because HCL has separate namespaces for functions and variables, we need to use different punctuation for each to avoid creating parsing ambiguity that could be resolved only with infinite lookahead.
We cannot retroactively change the internal representation of function names to be a slice of names without breaking the existing API, and so we instead adopt a convention of packing the multi-part names into single strings which the parser guarantees will always be a series of valid identifiers separated by the literal
::sequence. That means that applications will make namespaced functions available in the EvalContext by naming them in a way that matches this convention.This addition should change nothing for any existing applications that only place single-identifier names in the EvalContext function table, but allows applications to begin defining such functions when they are ready, with whichever namespaces they deem appropriate.