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|
// Copyright 2014-2017 The html5ever Project Developers. See the
// COPYRIGHT file at the top-level directory of this distribution.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
/*!
Implements the `match_token!()` macro for use by the HTML tree builder
in `src/tree_builder/rules.rs`.
## Example
```rust
match_token!(token {
CommentToken(text) => 1,
tag @ <base> <link> <meta> => 2,
</head> => 3,
</body> </html> </br> => else,
tag @ </_> => 4,
token => 5,
})
```
## Syntax
Because of the simplistic parser, the macro invocation must
start with exactly `match_token!(token {` (with whitespace as specified)
and end with exactly `})`.
The left-hand side of each match arm is an optional `name @` binding, followed by
- an ordinary Rust pattern that starts with an identifier or an underscore, or
- a sequence of HTML tag names as identifiers, each inside "<...>" or "</...>"
to match an open or close tag respectively, or
- a "wildcard tag" "<_>" or "</_>" to match all open tags or all close tags
respectively.
The right-hand side is either an expression or the keyword `else`.
Note that this syntax does not support guards or pattern alternation like
`Foo | Bar`. This is not a fundamental limitation; it's done for implementation
simplicity.
## Semantics
Ordinary Rust patterns match as usual. If present, the `name @` binding has
the usual meaning.
A sequence of named tags matches any of those tags. A single sequence can
contain both open and close tags. If present, the `name @` binding binds (by
move) the `Tag` struct, not the outer `Token`. That is, a match arm like
```rust
tag @ <html> <head> => ...
```
expands to something like
```rust
TagToken(tag @ Tag { name: local_name!("html"), kind: StartTag })
| TagToken(tag @ Tag { name: local_name!("head"), kind: StartTag }) => ...
```
A wildcard tag matches any tag of the appropriate kind, *unless* it was
previously matched with an `else` right-hand side (more on this below).
The expansion of this macro reorders code somewhat, to satisfy various
restrictions arising from moves. However it provides the semantics of in-order
matching, by enforcing the following restrictions on its input:
- The last pattern must be a variable or the wildcard "_". In other words
it must match everything.
- Otherwise, ordinary Rust patterns and specific-tag patterns cannot appear
after wildcard tag patterns.
- No tag name may appear more than once.
- A wildcard tag pattern may not occur in the same arm as any other tag.
"<_> <html> => ..." and "<_> </_> => ..." are both forbidden.
- The right-hand side "else" may only appear with specific-tag patterns.
It means that these specific tags should be handled by the last,
catch-all case arm, rather than by any wildcard tag arm. This situation
is common in the HTML5 syntax.
*/
use quote::quote;
use syn::{braced, parse_quote, Token};
use proc_macro2::TokenStream;
use quote::ToTokens;
use std::collections::HashSet;
use std::fs::File;
use std::io::{Read, Write};
use std::path::Path;
use syn::ext::IdentExt;
use syn::fold::Fold;
use syn::parse::{Parse, ParseStream, Result};
pub fn expand(from: &Path, to: &Path) {
let mut source = String::new();
File::open(from)
.unwrap()
.read_to_string(&mut source)
.unwrap();
let ast = syn::parse_file(&source).expect("Parsing rules.rs module");
let mut m = MatchTokenParser {};
let ast = m.fold_file(ast);
let code = ast
.into_token_stream()
.to_string()
.replace("{ ", "{\n")
.replace(" }", "\n}");
File::create(to)
.unwrap()
.write_all(code.as_bytes())
.unwrap();
}
struct MatchTokenParser {}
struct MatchToken {
ident: syn::Ident,
arms: Vec<MatchTokenArm>,
}
struct MatchTokenArm {
binding: Option<syn::Ident>,
lhs: Lhs,
rhs: Rhs,
}
enum Lhs {
Tags(Vec<Tag>),
Pattern(syn::Pat),
}
enum Rhs {
Expression(syn::Expr),
Else,
}
#[derive(PartialEq, Eq, Hash, Clone)]
enum TagKind {
StartTag,
EndTag,
}
// Option is None if wildcard
#[derive(PartialEq, Eq, Hash, Clone)]
pub struct Tag {
kind: TagKind,
name: Option<syn::Ident>,
}
impl Parse for Tag {
fn parse(input: ParseStream) -> Result<Self> {
input.parse::<Token![<]>()?;
let closing: Option<Token![/]> = input.parse()?;
let name = match input.call(syn::Ident::parse_any)? {
ref wildcard if wildcard == "_" => None,
other => Some(other),
};
input.parse::<Token![>]>()?;
Ok(Tag {
kind: if closing.is_some() {
TagKind::EndTag
} else {
TagKind::StartTag
},
name,
})
}
}
impl Parse for Lhs {
fn parse(input: ParseStream) -> Result<Self> {
if input.peek(Token![<]) {
let mut tags = Vec::new();
while !input.peek(Token![=>]) {
tags.push(input.parse()?);
}
Ok(Lhs::Tags(tags))
} else {
let p = input.call(syn::Pat::parse_single)?;
Ok(Lhs::Pattern(p))
}
}
}
impl Parse for MatchTokenArm {
fn parse(input: ParseStream) -> Result<Self> {
let binding = if input.peek2(Token![@]) {
let binding = input.parse::<syn::Ident>()?;
input.parse::<Token![@]>()?;
Some(binding)
} else {
None
};
let lhs = input.parse::<Lhs>()?;
input.parse::<Token![=>]>()?;
let rhs = if input.peek(syn::token::Brace) {
let block = input.parse::<syn::Block>().unwrap();
let block = syn::ExprBlock {
attrs: vec![],
label: None,
block,
};
input.parse::<Option<Token![,]>>()?;
Rhs::Expression(syn::Expr::Block(block))
} else if input.peek(Token![else]) {
input.parse::<Token![else]>()?;
input.parse::<Token![,]>()?;
Rhs::Else
} else {
let expr = input.parse::<syn::Expr>().unwrap();
input.parse::<Option<Token![,]>>()?;
Rhs::Expression(expr)
};
Ok(MatchTokenArm { binding, lhs, rhs })
}
}
impl Parse for MatchToken {
fn parse(input: ParseStream) -> Result<Self> {
let ident = input.parse::<syn::Ident>()?;
let content;
braced!(content in input);
let mut arms = vec![];
while !content.is_empty() {
arms.push(content.parse()?);
}
Ok(MatchToken { ident, arms })
}
}
pub fn expand_match_token(body: &TokenStream) -> syn::Expr {
let match_token = syn::parse2::<MatchToken>(body.clone());
let ast = expand_match_token_macro(match_token.unwrap());
syn::parse2(ast).unwrap()
}
fn expand_match_token_macro(match_token: MatchToken) -> TokenStream {
let mut arms = match_token.arms;
let to_be_matched = match_token.ident;
// Handle the last arm specially at the end.
let last_arm = arms.pop().unwrap();
// Tags we've seen, used for detecting duplicates.
let mut seen_tags: HashSet<Tag> = HashSet::new();
// Case arms for wildcard matching. We collect these and
// emit them later.
let mut wildcards_patterns: Vec<TokenStream> = Vec::new();
let mut wildcards_expressions: Vec<syn::Expr> = Vec::new();
// Tags excluded (by an 'else' RHS) from wildcard matching.
let mut wild_excluded_patterns: Vec<TokenStream> = Vec::new();
let mut arms_code = Vec::new();
for MatchTokenArm { binding, lhs, rhs } in arms {
// Build Rust syntax for the `name @` binding, if any.
let binding = match binding {
Some(ident) => quote!(#ident @),
None => quote!(),
};
match (lhs, rhs) {
(Lhs::Pattern(_), Rhs::Else) => {
panic!("'else' may not appear with an ordinary pattern")
},
// ordinary pattern => expression
(Lhs::Pattern(pat), Rhs::Expression(expr)) => {
if !wildcards_patterns.is_empty() {
panic!(
"ordinary patterns may not appear after wildcard tags {:?} {:?}",
pat, expr
);
}
arms_code.push(quote!(#binding #pat => #expr,))
},
// <tag> <tag> ... => else
(Lhs::Tags(tags), Rhs::Else) => {
for tag in tags {
if !seen_tags.insert(tag.clone()) {
panic!("duplicate tag");
}
if tag.name.is_none() {
panic!("'else' may not appear with a wildcard tag");
}
wild_excluded_patterns.push(make_tag_pattern(&TokenStream::new(), tag));
}
},
// <_> => expression
// <tag> <tag> ... => expression
(Lhs::Tags(tags), Rhs::Expression(expr)) => {
// Is this arm a tag wildcard?
// `None` if we haven't processed the first tag yet.
let mut wildcard = None;
for tag in tags {
if !seen_tags.insert(tag.clone()) {
panic!("duplicate tag");
}
match tag.name {
// <tag>
Some(_) => {
if !wildcards_patterns.is_empty() {
panic!("specific tags may not appear after wildcard tags");
}
if wildcard == Some(true) {
panic!("wildcard tags must appear alone");
}
if wildcard.is_some() {
// Push the delimiter `|` if it's not the first tag.
arms_code.push(quote!( | ))
}
arms_code.push(make_tag_pattern(&binding, tag));
wildcard = Some(false);
},
// <_>
None => {
if wildcard.is_some() {
panic!("wildcard tags must appear alone");
}
wildcard = Some(true);
wildcards_patterns.push(make_tag_pattern(&binding, tag));
wildcards_expressions.push(expr.clone());
},
}
}
match wildcard {
None => panic!("[internal macro error] tag arm with no tags"),
Some(false) => arms_code.push(quote!( => #expr,)),
Some(true) => {}, // codegen for wildcards is deferred
}
},
}
}
// Time to process the last, catch-all arm. We will generate something like
//
// last_arm_token => {
// let enable_wildcards = match last_arm_token {
// TagToken(Tag { kind: EndTag, name: local_name!("body"), .. }) => false,
// TagToken(Tag { kind: EndTag, name: local_name!("html"), .. }) => false,
// // ...
// _ => true,
// };
//
// match (enable_wildcards, last_arm_token) {
// (true, TagToken(name @ Tag { kind: StartTag, .. }))
// => ..., // wildcard action for start tags
//
// (true, TagToken(name @ Tag { kind: EndTag, .. }))
// => ..., // wildcard action for end tags
//
// (_, token) => ... // using the pattern from that last arm
// }
// }
let MatchTokenArm { binding, lhs, rhs } = last_arm;
let (last_pat, last_expr) = match (binding, lhs, rhs) {
(Some(_), _, _) => panic!("the last arm cannot have an @-binding"),
(None, Lhs::Tags(_), _) => panic!("the last arm cannot have tag patterns"),
(None, _, Rhs::Else) => panic!("the last arm cannot use 'else'"),
(None, Lhs::Pattern(p), Rhs::Expression(e)) => (p, e),
};
quote! {
match #to_be_matched {
#(
#arms_code
)*
last_arm_token => {
let enable_wildcards = match last_arm_token {
#(
#wild_excluded_patterns => false,
)*
_ => true,
};
match (enable_wildcards, last_arm_token) {
#(
(true, #wildcards_patterns) => #wildcards_expressions,
)*
(_, #last_pat) => #last_expr,
}
}
}
}
}
impl Fold for MatchTokenParser {
fn fold_stmt(&mut self, stmt: syn::Stmt) -> syn::Stmt {
if let syn::Stmt::Item(syn::Item::Macro(syn::ItemMacro { ref mac, .. })) = stmt {
if mac.path == parse_quote!(match_token) {
return syn::fold::fold_stmt(
self,
syn::Stmt::Expr(expand_match_token(&mac.tokens), None),
);
}
}
syn::fold::fold_stmt(self, stmt)
}
fn fold_expr(&mut self, expr: syn::Expr) -> syn::Expr {
if let syn::Expr::Macro(syn::ExprMacro { ref mac, .. }) = expr {
if mac.path == parse_quote!(match_token) {
return syn::fold::fold_expr(self, expand_match_token(&mac.tokens));
}
}
syn::fold::fold_expr(self, expr)
}
}
fn make_tag_pattern(binding: &TokenStream, tag: Tag) -> TokenStream {
let kind = match tag.kind {
TagKind::StartTag => quote!(crate::tokenizer::StartTag),
TagKind::EndTag => quote!(crate::tokenizer::EndTag),
};
let name_field = if let Some(name) = tag.name {
let name = name.to_string();
quote!(name: local_name!(#name),)
} else {
quote!()
};
quote! {
crate::tree_builder::types::TagToken(#binding crate::tokenizer::Tag { kind: #kind, #name_field .. })
}
}
|
