Optionally transform Extend fields to add items one by one
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -1,4 +1,4 @@ | ||
| use proc_macro2::{Span, TokenStream}; | ||
| use quote::quote; | ||
| use syn::parse::Error; | ||
| use syn::spanned::Spanned; | ||
|
|
@@ -87,9 +87,22 @@ pub struct SetterSettings { | |
| pub doc: Option<syn::Expr>, | ||
| pub skip: bool, | ||
| pub auto_into: bool, | ||
| pub strip_collection: Option<StripCollection>, | ||
| pub strip_option: bool, | ||
| } | ||
|
|
||
| #[derive(Debug, Clone)] | ||
| pub struct StripCollection { | ||
| pub keyword_span: Span, | ||
| pub from_first: Option<FromFirst>, | ||
| } | ||
|
|
||
| #[derive(Debug, Clone)] | ||
| pub struct FromFirst { | ||
| pub keyword_span: Span, | ||
| pub closure: syn::ExprClosure, | ||
| } | ||
|
|
||
| impl FieldBuilderAttr { | ||
| pub fn with(mut self, attrs: &[syn::Attribute]) -> Result<Self, Error> { | ||
| let mut skip_tokens = None; | ||
|
|
@@ -232,6 +245,58 @@ impl SetterSettings { | |
| _ => Err(Error::new_spanned(&assign, format!("Unknown parameter {:?}", name))), | ||
| } | ||
| } | ||
| syn::Expr::Call(call) => { | ||
| let name = | ||
| expr_to_single_string(&call.func).ok_or_else(|| Error::new_spanned(&call.func, "Expected identifier"))?; | ||
| match name.as_str() { | ||
| "strip_collection" => { | ||
| if self.strip_collection.is_some() { | ||
| Err(Error::new( | ||
| call.span(), | ||
| "Illegal setting - field is already calling extend(...) with the argument", | ||
| )) | ||
| } else if let Some(attr) = call.attrs.first() { | ||
| Err(Error::new_spanned(attr, "Unexpected attribute")) | ||
| } else { | ||
| let mut strip_collection = StripCollection { | ||
| keyword_span: name.span(), | ||
| from_first: None, | ||
| }; | ||
| for arg in call.args { | ||
| match arg { | ||
| syn::Expr::Assign(assign) => { | ||
| let name = expr_to_single_string(&assign.left) | ||
| .ok_or_else(|| Error::new_spanned(&assign.left, "Expected identifier"))?; | ||
| match name.as_str() { | ||
| "from_first" => match *assign.right { | ||
| syn::Expr::Closure(closure) => { | ||
| strip_collection.from_first = Some(FromFirst { | ||
| keyword_span: assign.left.span(), | ||
| closure, | ||
| }) | ||
| } | ||
| other => { | ||
| return Err(Error::new_spanned(other, "Expected closure (|first| <...>)")) | ||
| } | ||
| }, | ||
| _ => { | ||
| return Err(Error::new_spanned( | ||
| &assign.left, | ||
| format!("Unknown parameter {:?}", name), | ||
| )) | ||
| } | ||
| } | ||
| } | ||
| _ => return Err(Error::new_spanned(arg, "Expected (<...>=<...>)")), | ||
| } | ||
| } | ||
| self.strip_collection = Some(strip_collection); | ||
| Ok(()) | ||
| } | ||
| } | ||
| _ => Err(Error::new_spanned(&call.func, format!("Unknown parameter {:?}", name))), | ||
| } | ||
| } | ||
| syn::Expr::Path(path) => { | ||
| let name = path_to_single_string(&path.path).ok_or_else(|| Error::new_spanned(&path, "Expected identifier"))?; | ||
| macro_rules! handle_fields { | ||
|
|
@@ -247,6 +312,17 @@ impl SetterSettings { | |
| } | ||
| } | ||
| )* | ||
| "strip_collection" => { | ||
| if self.strip_collection.is_some() { | ||
| Err(Error::new(path.span(), "Illegal setting - field is already calling extend(...) with the argument")) | ||
| } else { | ||
| self.strip_collection = Some(StripCollection{ | ||
| keyword_span: name.span(), | ||
| from_first: None | ||
| }); | ||
| Ok(()) | ||
| } | ||
| } | ||
| _ => Err(Error::new_spanned( | ||
| &path, | ||
| format!("Unknown setter parameter {:?}", name), | ||
|
|
@@ -281,6 +357,10 @@ impl SetterSettings { | |
| self.auto_into = false; | ||
| Ok(()) | ||
| } | ||
| "strip_collection" => { | ||
| self.strip_collection = None; | ||
| Ok(()) | ||
| } | ||
| "strip_option" => { | ||
| self.strip_option = false; | ||
| Ok(()) | ||
|
|
@@ -291,7 +371,7 @@ impl SetterSettings { | |
| Err(Error::new_spanned(expr, "Expected simple identifier".to_owned())) | ||
| } | ||
| } | ||
| _ => Err(Error::new_spanned(expr, "Expected (<...>=<...>) or (<...>(<...>))")), | ||
|
There was a problem hiding this comment. I wasn't sure about the placeholder syntax here, but I think I got "assignment or call" right. There was a problem hiding this comment. Maybe using Lookahead1 would make sense here, since that can generate a similar error message automatically. The syntax isn't as clean as the match statement here, though. |
||
| } | ||
| } | ||
| } | ||
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I think
from_firstis more clear thaninitializerhere, and will nicely pair withfrom_iteronce added.I'm concerned about what to default to if just one of the parameters is present, or with empty parentheses.
My current hunch is that initialisers missing from explicit parentheses shouldn't be generated at all, but also to accept
from_firstandfrom_iterwithout assignment to generate the default each. This would mirror howdefaultworks asbuilder(…)parameter.I could also add support for
!from_firstand!from_iterto delete them again once set, but that feels a bit odd to me.Is there a specific reason this is supported on the fields? The application I can think of is for overrides when combined with a macro, but I'm just guessing here 🤔
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Is
from_firstwithout arguments even meaningful? What would be the default?As for
from_iter- I think maybe it should be the default - as in, without an argument you won't even need to specify it. Instead of keeping the actual target collection we can keepI: Iterator, and each time we extend with the builder, we can make anstd::iter::Chain. We can still specifyfrom_iter = |it| ...ifFromIteratoris not available for that collection or if for whatever reason we need custom behavior.