From ac65d482c4bae8a98feb0d74e2cbe797b61c1d84 Mon Sep 17 00:00:00 2001
From: Lars Wirzenius <liw@liw.fi>
Date: Sat, 3 Sep 2022 11:39:03 +0300
Subject: refactor: AST only parses Markdown, YAML is extracted outside it

Sponsored-by: author
---
 src/ast.rs | 31 ++++++++-----------------------
 src/doc.rs |  4 ++--
 2 files changed, 10 insertions(+), 25 deletions(-)

diff --git a/src/ast.rs b/src/ast.rs
index afa8b3b..f02fdd1 100644
--- a/src/ast.rs
+++ b/src/ast.rs
@@ -29,10 +29,9 @@ pub struct AbstractSyntaxTree {
 }
 
 impl AbstractSyntaxTree {
-    // Create a new AST.
-    //
-    // Note that this is not public.
-    fn new(meta: YamlMetadata, blocks: Vec<Block>) -> Self {
+    /// Create a new AST.
+    pub fn new(meta: YamlMetadata, markdown: &str) -> Self {
+        let blocks = parse_blocks(markdown);
         Self { blocks, meta }
     }
 
@@ -46,20 +45,6 @@ impl AbstractSyntaxTree {
     }
 }
 
-impl std::str::FromStr for AbstractSyntaxTree {
-    type Err = Error;
-
-    /// Create an abstract syntax tree from a string.
-    fn from_str(markdown: &str) -> Result<Self, Self::Err> {
-        trace!("Parsing markdown into AST");
-        let (meta, markdown) = extract_metadata(markdown)?;
-        let blocks = parse_blocks(markdown);
-        let ast = AbstractSyntaxTree::new(meta, blocks);
-        trace!("Parsing markdown: OK");
-        Ok(ast)
-    }
-}
-
 /// Extract YAML metadata from a Markdown document.
 pub fn extract_metadata(markdown: &str) -> Result<(YamlMetadata, &str), Error> {
     trace!("Extracting YAML from Markdown");
@@ -382,10 +367,8 @@ fn meta_path_bufs(v: &[PathBuf]) -> MetaValue {
 
 #[cfg(test)]
 mod test {
-    use super::{parse_code_block_attrs, AbstractSyntaxTree, YamlMetadata};
-    use super::{Block, Inline};
+    use super::{extract_metadata, parse_code_block_attrs, AbstractSyntaxTree, YamlMetadata};
     use std::path::PathBuf;
-    use std::str::FromStr;
 
     #[test]
     fn code_block_attrs() {
@@ -411,7 +394,8 @@ mod test {
     #[test]
     fn parses_leading_meta() {
         let markdown = "\n\n---\ntitle: Foo Bar\n...\nfoobar\n";
-        let ast = AbstractSyntaxTree::from_str(markdown).unwrap();
+        let (meta, markdown) = extract_metadata(markdown).unwrap();
+        let ast = AbstractSyntaxTree::new(meta, markdown);
         let doc = ast.to_pandoc();
         let keys: Vec<String> = doc.meta.keys().cloned().collect();
         assert_eq!(keys, ["title"]);
@@ -420,7 +404,8 @@ mod test {
     #[test]
     fn parses_trailing_meta() {
         let markdown = "foobar\n---\ntitle: Foo Bar\n...\n\n\n";
-        let ast = AbstractSyntaxTree::from_str(markdown).unwrap();
+        let (meta, markdown) = extract_metadata(markdown).unwrap();
+        let ast = AbstractSyntaxTree::new(meta, markdown);
         let doc = ast.to_pandoc();
         let keys: Vec<String> = doc.meta.keys().cloned().collect();
         assert_eq!(keys, ["title"]);
diff --git a/src/doc.rs b/src/doc.rs
index ace3e67..2f3368e 100644
--- a/src/doc.rs
+++ b/src/doc.rs
@@ -20,7 +20,6 @@ use std::default::Default;
 use std::fmt::Debug;
 use std::ops::Deref;
 use std::path::{Path, PathBuf};
-use std::str::FromStr;
 
 use pandoc_ast::{MutVisitor, Pandoc};
 
@@ -208,7 +207,8 @@ impl Document {
         let filename = filename.to_path_buf();
         let markdown = std::fs::read_to_string(&filename)
             .map_err(|err| SubplotError::ReadFile(filename.clone(), err))?;
-        let ast = ast::AbstractSyntaxTree::from_str(&markdown)?;
+        let (meta, markdown) = ast::extract_metadata(&markdown)?;
+        let ast = ast::AbstractSyntaxTree::new(meta, markdown);
 
         trace!("Parsed document OK");
         Self::from_ast(basedir, vec![filename], ast.to_pandoc(), style, template)
-- 
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