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//! This crate provides the `duplicate` attribute macro for //! code duplication with substitution. //! //! # Usage //! //! Say you have a trait with a method `is_max` that should return `true` if the //! value of the object is the maximum allowed and `false` otherwise: //! ``` //! trait IsMax { //! fn is_max(&self) -> bool; //! } //! ``` //! You would like to implement this trait for the three integer types `u8`, //! `u16`, and `u32`: //! //! ``` //! # trait IsMax {fn is_max(&self) -> bool;} //! impl IsMax for u8 { //! fn is_max(&self) -> bool { //! *self == 255 //! } //! } //! impl IsMax for u16 { //! fn is_max(&self) -> bool { //! *self == 65_535 //! } //! } //! impl IsMax for u32 { //! fn is_max(&self) -> bool { //! *self == 4_294_967_295 //! } //! } //! ``` //! This is a lot of repetition. Only the type and the maximum value are //! actually different between the three implementations. This might not be much //! in our case, but imagine doing this for all the integer types (10, as of the //! last count.) We can use the `duplicate` attribute to avoid repeating //! ourselves: //! //! ``` //! # trait IsMax {fn is_max(&self) -> bool;} //! use duplicate::duplicate; //! #[duplicate( //! int_type [ u8 ] [ u16 ] [ u32 ] //! max_value [ 255 ] [ 65_535 ] [ 4_294_967_295 ] //! )] //! impl IsMax for int_type { //! fn is_max(&self) -> bool { //! *self == max_value //! } //! } //! //! assert!(!42u8.is_max()); //! assert!(!42u16.is_max()); //! assert!(!42u32.is_max()); //! ``` //! The above code will expand to the three implementations before it. //! The attribute invocation specifies that the following item should be //! substituted by three duplicates of itself. Additionally, each occurrence of //! the identifier `int_type` in the first duplicate should be replaced by `u8`, //! in the second duplicate by `u16`, and in the last by `u32`. Likewise, each //! occurrence of `max_value` should be replaced by `255`, `65_535`, and //! `4_294_967_295` in the first, second, and third duplicates respectively. //! //! `int_type` and `max_value` are called _substitution identifiers_, while `[ //! u8 ]`, `[ u16 ]`, and `[ u32 ]` are each _substitutions_ for `int_type`. The //! number of duplicates made is equal to the number of substitutions the //! substitution identifiers have---all identifiers must have the same number of //! substitutions. Substitution identifiers must be valid Rust identifiers. //! //! The code inside substitutions can be arbitrary, as long as the expanded code //! is valid. Additionally, any "bracket" type is valid; we could have used `()` //! or `{}` anywhere `[]` is used in these examples. //! //! ## Verbose Syntax //! //! The syntax used in the previous examples is the _short syntax_. //! `duplicate` also accepts a _verbose syntax_ that is less concise, but more //! powerful. Using the verbose syntax, the above usage looks like this: //! ``` //! # trait IsMax {fn is_max(&self) -> bool;} //! use duplicate::duplicate; //! #[duplicate( //! [ //! int_type [ u8 ] //! max_value [ 255 ] //! ] //! [ //! int_type [ u16 ] //! max_value [ 65_535 ] //! ] //! [ //! int_type [ u32 ] //! max_value [ 4_294_967_295 ] //! ] //! )] //! impl IsMax for int_type { //! fn is_max(&self) -> bool { //! *self == max_value //! } //! } //! //! # assert!(!42u8.is_max()); //! # assert!(!42u16.is_max()); //! # assert!(!42u32.is_max()); //! ``` //! The verbose syntax is centered around the _substitution group_, which then //! includes a set of identifier and substitution pairs. Here is an annotated //! version of the same code: //! ``` //! # trait IsMax {fn is_max(&self) -> bool;} //! # use duplicate::duplicate; //! #[duplicate( //! [ //-+ //! int_type [ u8 ] // | Substitution group 1 //! max_value [ 255 ] // | //! // ^^^^^^^^^ ^^^^^^^ substitution | //! // | | //! // substitution identifier | //! ] //-+ //! [ //-+ //! int_type [ u16 ] // | Substitution group 2 //! max_value [ 65_535 ] // | //! ] //-+ //! [ //-+ //! max_value [ 4_294_967_295 ] // | Substitution group 3 //! int_type [ u32 ] // | //! ] //-+ //! )] //! # impl IsMax for int_type { //! # fn is_max(&self) -> bool { //! # *self == max_value //! # } //! # } //! # //! # assert!(!42u8.is_max()); //! # assert!(!42u16.is_max()); //! # assert!(!42u32.is_max()); //! ``` //! Note that in each substitution group every identifier must have exactly one //! substitution. Any number of groups can be given with each translating to one //! duplicate. All the groups must have the exact same identifiers, though the //! order in which they arrive in each group is not important. For example, in //! the annotated example, the third group has the `max_value` identifier before //! `int_type` without having any effect on the expanded code. //! //! The short syntax's substitution grouping is based on the order of the //! substitutions for each identifier. We can annotate the short version of our //! example to highlight this: //! ``` //! # trait IsMax {fn is_max(&self) -> bool;} //! # use duplicate::duplicate; //! #[duplicate(// vvvvvvv Group 1 vvvvvvvvvvvvvvvvv Group3 //! integer_type [ u8 ] [ u16 ] [ u32 ] //! max_value [ 255 ] [ 65_535 ] [ 4_294_967_295 ] //! )]// ^^^^^^^^^^ Group 2 //! # impl IsMax for integer_type { //! # fn is_max(&self) -> bool { //! # *self == max_value //! # } //! # } //! # //! # assert!(!42u8.is_max()); //! # assert!(!42u16.is_max()); //! # assert!(!42u32.is_max()); //! ``` //! The verbose syntax is not very concise but it has various advantages over //! the shorter syntax: //! //! * Individual substitution groups can be commented out easily for debugging //! or other purposes. //! * Because it grows horizontally, the short syntax becomes unwieldy for large //! numbers of //! duplicates, easily overflowing the 100 character line bound convension that //! the Rust community strives for. When this happens, either the //! substitutions must be aligned vertically, making it difficult to identify //! substitution groups, or it must be converted to the verbose //! to ensure line bounds are respected. //! * Along the same lines, if the contents of a substitution are long, the //! short syntax again //! suffers the same problems. //! * And lastly, the verbose syntax offers something the short doesn't: nested //! invocation. //! //! ### Nested Invocation //! //! Imagine we have the following trait with the method `is_negative` that //! should return `true` if the value of the object is negative and `false` //! otherwise: //! ``` //! trait IsNegative { //! fn is_negative(&self) -> bool; //! } //! ``` //! We want to implement this for the six integer types `u8`, `u16`, `u32`, //! `i8`, `i16`, and `i32`. For the first three types, which are all unsigned, //! the implementation of this trait should trivially return `false` as they //! can't be negative. However, for the remaining, signed types their //! implementations is identical (checking whether they are less than `0`), but, //! of course, different from the first three: //! ``` //! # trait IsNegative { fn is_negative(&self) -> bool;} //! impl IsNegative for u8 { //! fn is_negative(&self) -> bool { //! false //! } //! } //! impl IsNegative for u16 { //! fn is_negative(&self) -> bool { //! false //! } //! } //! impl IsNegative for u32 { //! fn is_negative(&self) -> bool { //! false //! } //! } //! impl IsNegative for i8 { //! fn is_negative(&self) -> bool { //! *self < 0 //! } //! } //! impl IsNegative for i16 { //! fn is_negative(&self) -> bool { //! *self < 0 //! } //! } //! impl IsNegative for i32 { //! fn is_negative(&self) -> bool { //! *self < 0 //! } //! } //! # assert!(!42u8.is_negative()); //! # assert!(!42u16.is_negative()); //! # assert!(!42u32.is_negative()); //! # assert!(!42i8.is_negative()); //! # assert!(!42i16.is_negative()); //! # assert!(!42i32.is_negative()); //! ``` //! Notice how the code repetition is split over 2 axes: 1) They all implement //! the same trait 2) the method implementations of the first 3 are identical to //! each other but different to the next 3, which are also mutually identical. //! To implement this using only the syntax we have already seen, we could do //! something like this: //! ``` //! # trait IsNegative { fn is_negative(&self) -> bool;} //! # use duplicate::duplicate; //! #[duplicate( //! [ //! int_type [ u8 ] //! implementation [ false ] //! ] //! [ //! int_type [ u16 ] //! implementation [ false ] //! ] //! [ //! int_type [ u32 ] //! implementation [ false ] //! ] //! [ //! int_type [ i8 ] //! implementation [ *self < 0 ] //! ] //! [ //! int_type [ i16 ] //! implementation [ *self < 0 ] //! ] //! [ //! int_type [ i32 ] //! implementation [ *self < 0 ] //! ] //! )] //! impl IsNegative for int_type { //! fn is_negative(&self) -> bool { //! implementation //! } //! } //! //! assert!(!42u8.is_negative()); //! assert!(!42u16.is_negative()); //! assert!(!42u32.is_negative()); //! assert!(!42i8.is_negative()); //! assert!(!42i16.is_negative()); //! assert!(!42i32.is_negative()); //! ``` //! However ironically, we here had to repeat ourselves in the macro invocation //! instead of the code: we needed to repeat the implementations `[ false ]` and //! `[ *self < 0 ]` three times each. Using verbose syntax we can utilize //! _nested invocation_ to remove the last bit of repetition: //! //! ``` //! # trait IsNegative { fn is_negative(&self) -> bool;} //! # use duplicate::duplicate; //! #[duplicate( //! #[ //! int_type_nested [u8] [u16] [u32] //! ][ //! [ //! int_type [ int_type_nested ] //! implementation [ false ] //! ] //! ] //! #[ //! int_type_nested [i8] [i16] [i32] //! ][ //! [ //! int_type [ int_type_nested ] //! implementation [ *self < 0 ] //! ] //! ] //! )] //! impl IsNegative for int_type { //! fn is_negative(&self) -> bool { //! implementation //! } //! } //! //! assert!(!42u8.is_negative()); //! assert!(!42u16.is_negative()); //! assert!(!42u32.is_negative()); //! assert!(!42i8.is_negative()); //! assert!(!42i16.is_negative()); //! assert!(!42i32.is_negative()); //! ``` //! //! We use `#` to invoke the macro inside itself, producing duplicates //! of the code inside the following `[]`, `{}`, or `()`. //! In our example, we have 2 invocations that each produce 3 groups, inserting //! the correct `implementation` for their signed or unsigned types. //! The above nested invocation is equivalent to the previous, non-nested //! invocation, and actually expands to it as an intermediate step before //! expanding the outer-most invocation. //! //! It's important to notice that the nested invocation doesn't know it //! isn't the outer-most invocation and therefore doesn't discriminate between //! identifiers. We had to use a different identifier in the nested invocations //! (`int_type_nested`) than in the code (`int_type`), because otherwise the //! nested invocation would substitute the substitution identifier, too, instead //! of only substituting in the nested invocation's substitute. //! //! Nested invocation is only possible when using verbose syntax. //! Additionally, the nested invocations must produce verbose syntax of their //! parent invocation. However, each nested invocation's private syntax is free //! to use the short version. Notice in our above example, the nested //! invocations use short syntax but produce verbose syntax for the outer-most //! invocation. //! //! There is no limit on the depth of nesting, however, as might be clear from //! our example, it can get complicated to read. Additionally, the syntax used //! in any invocation that includes a nested invocation must be verbose. //! //! Lastly, we should note that we can have nested invocations interleaved with //! normal substution groups. For example, say we want to implement `IsNegative` //! for `i8`, but don't want the same for `i16` and `i32`. We could do the //! following: //! //! ``` //! # trait IsNegative { fn is_negative(&self) -> bool;} //! # use duplicate::duplicate; //! #[duplicate( //! #[ // -+ //! int_type_nested [u8] [u16] [u32] // | //! ][ // | //! [ // | Nested invocation producing 3 //! int_type [ int_type_nested ] // | substitution groups //! implementation [ false ] // | //! ] // | //! ] // -+ //! [ // -+ //! int_type [ i8 ] // | Substitution group 4 //! implementation [ *self < 0 ] // | //! ] // -+ //! )] //! impl IsNegative for int_type { //! fn is_negative(&self) -> bool { //! implementation //! } //! } //! //! # assert!(!42u8.is_negative()); //! # assert!(!42u16.is_negative()); //! # assert!(!42u32.is_negative()); //! # assert!(!42i8.is_negative()); //! ``` //! //! # Disclaimer //! //! This crate does not try to justify or condone the usage of code duplication //! instead of proper abstractions. //! This macro should only be used where it is not possible to reduce code //! duplication through other means, or where it simply is not worth it. //! //! As an example, libraries that have two or more structs/traits with similar //! APIs might use this macro to test them without having to copy-paste test //! cases and manually make the needed edits. use proc_macro::{token_stream::IntoIter, Delimiter, Group, Span, TokenStream, TokenTree}; use proc_macro_error::{ proc_macro::{Punct, Spacing}, *, }; use std::collections::{HashMap, HashSet}; /// Duplicates and substitutes given identifiers for different code in each /// duplicate. /// /// _Substitution identifiers_ can be inserted into the code, which will be /// substituted with the different given code in each duplicate version of the /// original code. /// /// # Short Syntax /// ``` /// use duplicate::duplicate; /// trait IsMax { /// fn is_max(&self) -> bool; /// } /// /// #[duplicate( /// int_type [ u8 ] [ u16 ] [ u32 ] /// max_value [ 255 ] [ 65_535 ] [ 4_294_967_295 ] /// )] /// impl IsMax for int_type { /// fn is_max(&self) -> bool { /// *self == max_value /// } /// } /// /// assert!(!42u8.is_max()); /// assert!(!42u16.is_max()); /// assert!(!42u32.is_max()); /// ``` /// The implementation of `IsMax` is duplicated 3 times: /// /// 1. For the type `u8` and the its maximum value `255`. /// 2. For the type `u16` and the its maximum value `65_535 `. /// 3. For the type `u32` and the its maximum value `4_294_967_295 `. /// /// This syntax must start with an identifier and then provice a set of /// substitutions for it. The substitutions must be enclosed in `[]`, `{}`, or /// `()`, but are otherwise free. Then another substituion identifier with the /// same number of substitutions as the previous identifier. Repeat as many as /// necessary. /// /// # Verbose Syntax /// /// ``` /// use duplicate::duplicate; /// trait IsMax { /// fn is_max(&self) -> bool; /// } /// /// #[duplicate( /// [ /// int_type [ u8 ] /// max_value [ 255 ] /// ] /// [ /// int_type [ u16 ] /// max_value [ 65_535 ] /// ] /// [ /// max_value [ 4_294_967_295 ] /// int_type [ u32 ] /// ] /// )] /// impl IsMax for int_type { /// fn is_max(&self) -> bool { /// *self == max_value /// } /// } /// /// assert!(!42u8.is_max()); /// assert!(!42u16.is_max()); /// assert!(!42u32.is_max()); /// ``` /// Has the same functionality as the previous short-syntax example. /// /// For each duplicate needed, a _substitution group_ must be given enclosed in /// `[]`, `{}`, or `()`. A substitution group is a set of identifiers and /// substitution pairs, like in the short syntax, but there can only be one /// substitution per identifier. All substitution groups must have the same /// identifiers, however their order is unimportant, as can be seen from the /// last substitution group above, where `max_value` comes before `int_type`. /// /// # Nested Invocation /// ``` /// use duplicate::duplicate; /// trait IsNegative { /// fn is_negative(&self) -> bool; /// } /// /// #[duplicate( /// #[ // -+ /// int_type_nested [u8] [u16] [u32] // | /// ][ // | /// [ // | Nested invocation producing 3 /// int_type [ int_type_nested ] // | substitution groups /// implementation [ false ] // | /// ] // | /// ] // -+ /// [ // -+ /// int_type [ i8 ] // | Substitution group 4 /// implementation [ *self < 0 ] // | /// ] // -+ /// )] /// impl IsNegative for int_type { /// fn is_negative(&self) -> bool { /// implementation /// } /// } /// /// assert!(!42u8.is_negative()); /// assert!(!42u16.is_negative()); /// assert!(!42u32.is_negative()); /// assert!(!42i8.is_negative()); /// ``` /// /// This implements `IsNegative` 4 times: /// /// 1. For the type `u8` with the implementation of the method simply returning /// `false`. 2. For the type `u16` the same way as `u8`. /// 3. For the type `u32` the same way as `u8` and `u16`. /// 4. For `i8` with the implementation of the method checking whether it's less /// than `0`. /// /// We used `#` to start a _nested invocation_ of the macro. In it, we use the /// identifier `int_type_nested` to substitute the 3 unsigned integer types into /// the body of the nested invocation, which is a substitution group for the /// outer macro invocation. This therefore produces the three substitution /// groups that makes the outer macro make the duplicates for the unsigned /// integers. /// /// This code is identical to the following, which doesn't use nested /// invocation: /// /// ``` /// # use duplicate::duplicate; /// # trait IsNegative { /// # fn is_negative(&self) -> bool; /// # } /// #[duplicate( /// [ /// int_type [ u8 ] /// implementation [ false ] /// ] /// [ /// int_type [ u16 ] /// implementation [ false ] /// ] /// [ /// int_type [ u32 ] /// implementation [ false ] /// ] /// [ /// int_type [ i8 ] /// implementation [ *self < 0 ] /// ] /// )] /// impl IsNegative for int_type { /// fn is_negative(&self) -> bool { /// implementation /// } /// } /// # assert!(!42u8.is_negative()); /// # assert!(!42u16.is_negative()); /// # assert!(!42u32.is_negative()); /// # assert!(!42i8.is_negative()); /// ``` #[proc_macro_attribute] #[proc_macro_error] pub fn duplicate(attr: TokenStream, item: TokenStream) -> TokenStream { match duplicate_impl(attr, item, false) { Ok(result) => result, Err(err) => abort!(err.0, err.1), } } /// Implements the macro. /// /// `allow_short`: If true, accepts short syntax fn duplicate_impl( attr: TokenStream, item: TokenStream, disallow_short: bool, ) -> Result<TokenStream, (Span, String)> { let subs = parse_attr(attr, Span::call_site(), disallow_short)?; let result = substitute(item, subs); Ok(result) } fn parse_attr( attr: TokenStream, stream_span: Span, disallow_short: bool, ) -> Result<Vec<HashMap<String, TokenStream>>, (Span, String)> { if identify_syntax(attr.clone(), stream_span, disallow_short)? { validate_verbose_attr(attr) } else { let valid = validate_short_attr(attr)?; let mut reorder = Vec::new(); let substitutions = valid; for _ in 0..substitutions[0].1.len() { reorder.push(HashMap::new()); } for (ident, subs) in substitutions { for (idx, sub) in subs.into_iter().enumerate() { reorder[idx].insert(ident.clone(), sub); } } Ok(reorder) } } /// True is verbose, false is short fn identify_syntax( attr: TokenStream, stream_span: Span, disallow_short: bool, ) -> Result<bool, (Span, String)> { if let Some(token) = attr.into_iter().next() { match token { TokenTree::Group(group) => { check_delimiter(group)?; Ok(true) }, TokenTree::Ident(_) if !disallow_short => Ok(false), TokenTree::Punct(p) if is_nested_invocation(&p) => Ok(true), _ if disallow_short => { Err(( token.span(), "Expected substitution group (Short syntax is disallowed at this level). \ Received neither." .into(), )) }, _ => { Err(( token.span(), "Expected substitution identifier or group. Received neither.".into(), )) }, } } else { Err((stream_span, "No substitutions found.".into())) } } fn validate_verbose_attr( attr: TokenStream, ) -> Result<Vec<HashMap<String, TokenStream>>, (Span, String)> { if attr.is_empty() { return Err((Span::call_site(), "No substitutions found.".into())); } let mut sub_groups = Vec::new(); let mut iter = attr.into_iter(); let mut substitution_ids = None; loop { if let Some(tree) = iter.next() { match tree { TokenTree::Punct(p) if is_nested_invocation(&p) => { let hints = "Hint: '#' is a nested invocation of the macro and must therefore \ be followed by a group containing the \ invocation.\nExample:\n#[\n\tidentifier [ substitute1 ] [ \ substitute2 ]\n][\n\tCode to be substituted whenever \ 'identifier' occurs \n]"; let nested_attr = parse_group(&mut iter, p.span(), hints)?; let nested_subs = parse_attr(nested_attr.stream(), nested_attr.span(), false)?; let nested_item = parse_group(&mut iter, nested_attr.span(), hints)?; let nested_duplicated = substitute(nested_item.stream(), nested_subs); let subs = validate_verbose_attr(nested_duplicated)?; sub_groups.extend(subs.into_iter()); }, _ => { sub_groups.push(extract_verbose_substitutions(tree, &substitution_ids)?); if None == substitution_ids { substitution_ids = Some(sub_groups[0].keys().cloned().collect()) } }, } } else { break; } } Ok(sub_groups) } fn is_nested_invocation(p: &Punct) -> bool { p.as_char() == '#' && p.spacing() == Spacing::Alone } fn extract_verbose_substitutions( tree: TokenTree, existing: &Option<HashSet<String>>, ) -> Result<HashMap<String, TokenStream>, (Span, String)> { // Must get span now, before it's corrupted. let tree_span = tree.span(); let group = check_group( tree, "Hint: When using verbose syntax, a substitutions must be enclosed in a \ group.\nExample:\n..\n[\n\tidentifier1 [ substitution1 ]\n\tidentifier2 [ substitution2 \ ]\n]", )?; if group.stream().into_iter().count() == 0 { return Err((group.span(), "No substitution groups found.".into())); } let mut substitutions = HashMap::new(); let mut stream = group.stream().into_iter(); loop { if let Some(ident) = stream.next() { if let TokenTree::Ident(ident) = ident { let sub = parse_group( &mut stream, ident.span(), "Hint: A substitution identifier should be followed by a group containing the \ code to be inserted instead of any occurrence of the identifier.", )?; let ident_string = ident.to_string(); // Check have found the same as existing if let Some(idents) = existing { if !idents.contains(&ident_string) { return Err(( ident.span(), "Unfamiliar substitution identifier. '{}' is not present in previous \ substitution groups." .into(), )); } } substitutions.insert(ident_string, sub.stream()); } else { return Err(( ident.span(), "Expected substitution identifier, got something else.".into(), )); } } else { // Check no substitution idents are missing. if let Some(idents) = existing { let sub_idents = substitutions.keys().cloned().collect(); let diff: Vec<_> = idents.difference(&sub_idents).collect(); if diff.len() > 0 { let mut msg: String = "Missing substitutions. Previous substitutions groups \ had the following identifiers not present in this \ group: " .into(); for ident in diff { msg.push_str("'"); msg.push_str(&ident.to_string()); msg.push_str("' "); } return Err((tree_span, msg)); } } break; } } Ok(substitutions) } fn validate_short_attr(attr: TokenStream) -> Result<Vec<(String, Vec<TokenStream>)>, (Span, String)> { if attr.is_empty() { return Err((Span::call_site(), "No substitutions found.".into())); } let mut result: Vec<(String, Vec<TokenStream>)> = Vec::new(); let mut iter = attr.into_iter(); let mut next_token = iter.next(); loop { if let Some(ident) = next_token { next_token = iter.next(); if let TokenTree::Ident(ident) = ident { let mut substitutions = Vec::new(); loop { if let Some(TokenTree::Group(group)) = next_token { next_token = iter.next(); let group = check_delimiter(group)?; substitutions.push(group.stream()); } else { break; } } if substitutions.len() == 0 { return Err(( ident.span(), "Expected substitution identifier to be followed by at least one \ substitution." .into(), )); } if !result.is_empty() && (result[0].1.len() != substitutions.len()) { return Err(( ident.span(), format!( "Unexpected number of substitutions for identifier. Expected {}, was \ {}.", result[0].1.len(), substitutions.len() ), )); } result.push((ident.to_string(), substitutions)); } else { return Err((ident.span(), "Expected substitution identifier.".into())); } } else { break; } } Ok(result) } fn substitute(item: TokenStream, groups: Vec<HashMap<String, TokenStream>>) -> TokenStream { let mut result = TokenStream::new(); for substitutions in groups { for token in item.clone().into_iter() { result.extend(substitute_token_tree(token, &substitutions)) } } result } fn substitute_token_tree( tree: TokenTree, subtitutions: &HashMap<String, TokenStream>, ) -> TokenStream { let mut result = TokenStream::new(); match tree { TokenTree::Ident(ident) => { if let Some(stream) = subtitutions.get(&ident.to_string()) { result.extend(stream.clone().into_iter()); } else { result.extend(TokenStream::from(TokenTree::Ident(ident)).into_iter()); } }, TokenTree::Group(group) => { let mut substituted = TokenStream::new(); for token in group.stream().into_iter() { substituted.extend(substitute_token_tree(token, subtitutions)) } result.extend( TokenStream::from(TokenTree::Group(Group::new(group.delimiter(), substituted))) .into_iter(), ); }, _ => result.extend(TokenStream::from(tree).into_iter()), } result } fn parse_group(iter: &mut IntoIter, parent_span: Span, hints: &str) -> Result<Group, (Span, String)> { if let Some(tree) = iter.next() { check_group(tree, hints) } else { return Err(( parent_span, "Unexpected end of macro invocation. Expected '[', '{', or '('.\n".to_string() + hints, )); } } fn check_group(tree: TokenTree, hints: &str) -> Result<Group, (Span, String)> { if let TokenTree::Group(group) = tree { check_delimiter(group) } else { return Err(( tree.span(), "Unexpected token. Expected '[', '{', or '('.\n".to_string() + hints, )); } } fn check_delimiter(group: Group) -> Result<Group, (Span, String)> { if group.delimiter() == Delimiter::None { return Err(( group.span(), "Unexpected delimiter for group. Expected '[]','{}', or '()' but received non.".into(), )); } Ok(group) }