refactor: turn loading Markdown from a file into a constructor

Previously, we used the TryFrom<&Path> trait, but it's not clear that
converting a pathname into a Markdown value means reading it. An
associated function that reads a file is clearer.

Sponsored-by: author

2 files changed, 25 insertions, 30 deletions

diff --git a/src/doc.rs b/src/doc.rs
index e860726..faa3a84 100644
--- a/src/doc.rs
+++ b/src/doc.rs
@@ -13,7 +13,6 @@ use crate::{Metadata, YamlMetadata};
 use crate::{Warning, Warnings};
 
 use std::collections::HashSet;
-use std::convert::TryFrom;
 use std::default::Default;
 use std::fmt::Debug;
 use std::fs::read;
@@ -147,7 +146,7 @@ impl Document {
 
         let mdfile = meta.markdown();
         let mdfile = basedir.join(mdfile);
-        let mut md = Markdown::try_from(mdfile.as_path())?;
+        let mut md = Markdown::load_file(mdfile.as_path())?;
         md.set_metadata(&meta);
         let markdowns = vec![mdfile];
 
diff --git a/src/md.rs b/src/md.rs
index 59fdc1e..f43b462 100644
--- a/src/md.rs
+++ b/src/md.rs
@@ -9,7 +9,6 @@ use pandoc_ast::{Map, MetaValue, MutVisitor, Pandoc};
 use serde_yaml::{Mapping, Value};
 use std::cell::RefCell;
 use std::collections::HashSet;
-use std::convert::TryFrom;
 use std::path::{Path, PathBuf};
 
 mod panhelper;
@@ -25,6 +24,30 @@ pub struct Markdown {
 }
 
 impl Markdown {
+    /// Load a Markdown file.
+    pub fn load_file(filename: &Path) -> Result<Self, SubplotError> {
+        trace!("parsing file as markdown: {}", filename.display());
+        let mut pandoc = pandoc::new();
+        pandoc.add_input(&filename);
+        pandoc.set_input_format(
+            pandoc::InputFormat::Markdown,
+            vec![pandoc::MarkdownExtension::Citations],
+        );
+        pandoc.set_output_format(pandoc::OutputFormat::Json, vec![]);
+        pandoc.set_output(pandoc::OutputKind::Pipe);
+
+        // Add external Pandoc filters.
+        crate::policy::add_citeproc(&mut pandoc);
+
+        let json = match pandoc.execute().map_err(SubplotError::Pandoc)? {
+            pandoc::PandocOutput::ToBuffer(o) => o,
+            _ => return Err(SubplotError::NotJson),
+        };
+
+        let ast: Pandoc = serde_json::from_str(&json).map_err(SubplotError::AstJson)?;
+        Ok(Self::new(ast))
+    }
+
     fn new(pandoc: Pandoc) -> Self {
         Self {
             pandoc: RefCell::new(pandoc),
@@ -211,33 +234,6 @@ fn meta_path_bufs(v: &[PathBuf]) -> MetaValue {
     MetaValue::MetaList(v.iter().map(|p| meta_path_buf(p)).collect())
 }
 
-impl TryFrom<&Path> for Markdown {
-    type Error = SubplotError;
-
-    fn try_from(filename: &Path) -> Result<Self, Self::Error> {
-        trace!("parsing file as markdown: {}", filename.display());
-        let mut pandoc = pandoc::new();
-        pandoc.add_input(&filename);
-        pandoc.set_input_format(
-            pandoc::InputFormat::Markdown,
-            vec![pandoc::MarkdownExtension::Citations],
-        );
-        pandoc.set_output_format(pandoc::OutputFormat::Json, vec![]);
-        pandoc.set_output(pandoc::OutputKind::Pipe);
-
-        // Add external Pandoc filters.
-        crate::policy::add_citeproc(&mut pandoc);
-
-        let json = match pandoc.execute().map_err(SubplotError::Pandoc)? {
-            pandoc::PandocOutput::ToBuffer(o) => o,
-            _ => return Err(SubplotError::NotJson),
-        };
-
-        let ast: Pandoc = serde_json::from_str(&json).map_err(SubplotError::AstJson)?;
-        Ok(Self::new(ast))
-    }
-}
-
 fn extract_scenario(e: &[visitor::Element]) -> Result<(Option<Scenario>, usize), SubplotError> {
     if e.is_empty() {
         // If we get here, it's a programming error.