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refactor(cheddar): Extract code block highlighting into function

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Since I am going down the path of adding additional Markdown
extensions it makes sense to avoid letting `format_markdown` turn into
a giant beast of a function.

Therefore this commit extracts the logic for rendering code blocks via
syntect and changes the innards of `format_markdown` to instead
provide arbitrary AST value replacements.
This commit is contained in:
Vincent Ambo 2020-01-11 02:17:19 +00:00
parent 97f069db9e
commit d4e469508f
1 changed files with 47 additions and 37 deletions
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84
tools/cheddar/src/main.rs
View file

@ -1,4 +1,4 @@
use comrak::nodes::{AstNode, NodeValue, NodeHtmlBlock};
use comrak::nodes::{Ast, AstNode, NodeValue, NodeCodeBlock, NodeHtmlBlock};
use comrak::{Arena, parse_document, format_html, ComrakOptions};
use lazy_static::lazy_static;
use std::env;
@ -80,9 +80,48 @@ fn iter_nodes<'a, F>(node: &'a AstNode<'a>, f: &F) where F : Fn(&'a AstNode<'a>)
// Instead, try finding a syntax match by comparing case insensitively (for
// ASCII characters, anyways).
fn find_syntax_case_insensitive(info: &str) -> Option<&'static SyntaxReference> {
// TODO(tazjin): memoize this lookup
SYNTAXES.syntaxes().iter().rev().find(|&s| info.eq_ignore_ascii_case(&s.name))
}
// Replaces code-block inside of a Markdown AST with HTML blocks rendered by
// syntect. This enables static (i.e. no JavaScript) syntax highlighting, even
// of complex languages.
fn highlight_code_block(code_block: &NodeCodeBlock) -> NodeValue {
let theme = &THEMES.themes["InspiredGitHub"];
let info = String::from_utf8_lossy(&code_block.info);
let syntax = find_syntax_case_insensitive(&info)
.or_else(|| SYNTAXES.find_syntax_by_extension(&info))
.unwrap_or_else(|| SYNTAXES.find_syntax_plain_text());
let code = String::from_utf8_lossy(&code_block.literal);
let rendered = {
// Write the block preamble manually to get exactly the
// desired layout:
let mut hl = HighlightLines::new(syntax, theme);
let mut buf = BLOCK_PRE.to_string();
for line in LinesWithEndings::from(&code) {
let regions = hl.highlight(line, &SYNTAXES);
append_highlighted_html_for_styled_line(
&regions[..], IncludeBackground::No, &mut buf,
);
}
buf.push_str("</pre>");
buf
};
let block = NodeHtmlBlock {
block_type: 1, // It's unclear what behaviour is toggled by this
literal: rendered.into_bytes(),
};
NodeValue::HtmlBlock(block)
}
fn format_markdown() {
let document = {
let mut buffer = String::new();
@ -99,43 +138,14 @@ fn format_markdown() {
// replacing all code blocks with HTML blocks rendered by syntect.
iter_nodes(root, &|node| {
let mut ast = node.data.borrow_mut();
match &ast.value {
NodeValue::CodeBlock(code_block) => {
let theme = &THEMES.themes["InspiredGitHub"];
let info = String::from_utf8_lossy(&code_block.info);
let syntax = find_syntax_case_insensitive(&info)
.or_else(|| SYNTAXES.find_syntax_by_extension(&info))
.unwrap_or_else(|| SYNTAXES.find_syntax_plain_text());
let code = String::from_utf8_lossy(&code_block.literal);
let rendered = {
// Write the block preamble manually to get exactly the
// desired layout:
let mut hl = HighlightLines::new(syntax, theme);
let mut buf = BLOCK_PRE.to_string();
for line in LinesWithEndings::from(&code) {
let regions = hl.highlight(line, &SYNTAXES);
append_highlighted_html_for_styled_line(
&regions[..], IncludeBackground::No, &mut buf,
);
}
buf.push_str("</pre>");
buf
};
let block = NodeHtmlBlock {
block_type: 1, // It's unclear what behaviour is toggled by this
literal: rendered.into_bytes(),
};
ast.value = NodeValue::HtmlBlock(block);
},
_ => (),
let new = match &ast.value {
NodeValue::CodeBlock(code) => Some(highlight_code_block(code)),
_ => None,
};
if let Some(new_value) = new {
ast.value = new_value
}
});
format_html(root, &MD_OPTS, &mut io::stdout())