Allow globals to reference other globals #1734
Comments
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Relates to #461 |
#461 is unrelated actually. It was a potential evaluation scheme for comptime expressions but does not deal with what kinds of expressions we allow for globals. To provide more of a background on the reasoning why globals aren't allowed to reference other globals currently, if we allowed global MAX_ARGS = 8;
global PUBLIC_INPUTS_LEN = MAX_ARGS + 3;Then it follows that the following would also be possible: global MAX_ARGS = PUBLIC_INPUTS_LEN + 8;
global PUBLIC_INPUTS_LEN = MAX_ARGS + 3;Since globals, like functions are able to be referenced at a global scope before they're defined. We'd have to find a way to prevent circular dependencies like this in general with a good error message. Solving this is not as simple as "allow globals to reference other globals defined beforehand in the same file" since we must also worry about imports from other files and, if we allow function calls as well, functions that capture globals before they're defined such as: global BAD = init_bad();
fn init_bad() -> Field {
BAD + 1
}You can see how this function would clearly be erroneous but this can occur in more subtle ways accidentally as well. E.g. via indirectly called functions. |
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This was my mistake, I mis-remembered and thought we were using that as a potential to evaluate global constants with compile time expressions too |
jfecher
changed the title
# Description ## Problem\* Resolves #1122 ## Summary\* Adds a dependency graph to catch cases where structs will cyclically depend on one other. For example, the program: ```rs struct Foo { bar: Bar, } struct Bar { foo: Foo, } ``` Will now give the following error: ``` error: Dependency cycle found ┌─ /home/user/Code/Noir/noir/short/src/main.nr:6:1 │ 6 │ ╭ struct Bar { 7 │ │ foo: Foo, 8 │ │ } │ ╰─' 'Bar' recursively depends on itself: Bar -> Foo -> Bar │ ``` The error is still issued if these are split across separate modules. ## Additional Context Note that self-referential structs like `struct Foo { foo: Foo }` are not currently caught - we may need a separate check for this. This error is also only currently possible for cyclic struct dependencies, but once this is merged I'm going to expand this to more PRs to allow for globals and type aliases as well. This would implement #1734 as well as a similar feature to allow type aliases to reference other type aliases which is currently disallowed. ## Documentation\* Check one: - [x] No documentation needed. - [ ] Documentation included in this PR. - [ ] **[Exceptional Case]** Documentation to be submitted in a separate PR. # PR Checklist\* - [x] I have tested the changes locally. - [x] I have formatted the changes with [Prettier](https://prettier.io/) and/or `cargo fmt` on default settings. --------- Co-authored-by: kevaundray <[email protected]>
# Description ## Problem\* Resolves #1734 ## Summary\* Allows globals to be defined as any expression using the dependency graph to ensure there are no cycles. Note that globals defined via a function call are allowed: `global FOO = bar();`, although the function will be re-called each time the global is used since globals are just substituted for their definitions where they are used. Example program: ```rs global A = B; global B = foo(); fn foo() -> Field { A } ``` Example error: ``` error: Dependency cycle found ┌─ /Users/user/Code/Noir/noir/short/src/main.nr:2:8 │ 2 │ global B = foo(); │ - 'B' recursively depends on itself: B -> foo -> A -> B │ ``` ## Additional Context This is a somewhat longer PR because it also includes a refactoring to use a new `GlobalId` over `StmtId`. I found this necessary to allow referring to globals in cycles where another global may not be resolved yet. WIP because I still need to: - ~~Track dependencies within functions~~ - ~~Update documentation~~ ## Documentation\* Check one: - [ ] No documentation needed. - [x] Documentation included in this PR. - [ ] **[Exceptional Case]** Documentation to be submitted in a separate PR. # PR Checklist\* - [x] I have tested the changes locally. - [x] I have formatted the changes with [Prettier](https://prettier.io/) and/or `cargo fmt` on default settings. --------- Co-authored-by: José Pedro Sousa <[email protected]>
Problem
When writing modular code It sometimes happens that we have globals that depend on other globals, such as
However, this is not currently supported by the language, so we need to have explanatory comments and do searches to find usage which is quite error prone:
Happy Case
Globals could be the result of compile time arithmetic expressions. Even better if they can be the result of function calls that return comptime values, but just being able to define them with arithmetic expressions would be very helpful.
Alternatives Considered
No response
Additional Context
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Would you like to submit a PR for this Issue?
No
Support Needs
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