From 4892ab97637c3727834248aba19b0407439c1f5f Mon Sep 17 00:00:00 2001
From: Lars Wirzenius <liw@liw.fi>
Date: Sat, 28 Jan 2023 19:56:11 +0200
Subject: refactor: only mutating methods on Markdown require mutable self

Use RefCell's interior mutability to work around the fact that
pandoc_ast's MutVisitor requires a mutable reference to self.

Sponsored-by: author
---
 src/doc.rs |  2 +-
 src/md.rs  | 38 +++++++++++++++++---------------------
 2 files changed, 18 insertions(+), 22 deletions(-)

diff --git a/src/doc.rs b/src/doc.rs
index a39ab99..e860726 100644
--- a/src/doc.rs
+++ b/src/doc.rs
@@ -105,7 +105,7 @@ impl Document {
         subplot: PathBuf,
         markdowns: Vec<PathBuf>,
         yamlmeta: &YamlMetadata,
-        mut md: Markdown,
+        md: Markdown,
         style: Style,
         template: Option<&str>,
     ) -> Result<Document, SubplotError>
diff --git a/src/md.rs b/src/md.rs
index 6f00ab7..59fdc1e 100644
--- a/src/md.rs
+++ b/src/md.rs
@@ -7,6 +7,7 @@ use crate::{
 use log::trace;
 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};
@@ -20,21 +21,19 @@ use visitor::LintingVisitor;
 /// A parsed Markdown document.
 #[derive(Debug)]
 pub struct Markdown {
-    pandoc: Pandoc,
+    pandoc: RefCell<Pandoc>,
 }
 
 impl Markdown {
     fn new(pandoc: Pandoc) -> Self {
-        Self { pandoc }
-    }
-
-    fn pandoc(&mut self) -> &mut Pandoc {
-        &mut self.pandoc
+        Self {
+            pandoc: RefCell::new(pandoc),
+        }
     }
 
     /// Set document metadata from subplot.
     pub fn set_metadata(&mut self, meta: &YamlMetadata) {
-        self.pandoc.meta = to_pandoc_meta(meta);
+        self.pandoc.borrow_mut().meta = to_pandoc_meta(meta);
     }
 
     /// JSON representation of Pandoc AST.
@@ -44,17 +43,17 @@ impl Markdown {
     }
 
     /// Find problems.
-    pub fn lint(&mut self) -> Vec<SubplotError> {
+    pub fn lint(&self) -> Vec<SubplotError> {
         let mut linter = LintingVisitor::default();
-        linter.walk_pandoc(self.pandoc());
+        linter.walk_pandoc(&mut self.pandoc.borrow_mut());
         linter.issues
     }
 
     /// Find included images.
-    pub fn images(&mut self) -> Vec<PathBuf> {
+    pub fn images(&self) -> Vec<PathBuf> {
         let mut names = vec![];
         let mut visitor = visitor::ImageVisitor::new();
-        visitor.walk_pandoc(self.pandoc());
+        visitor.walk_pandoc(&mut self.pandoc.borrow_mut());
         for x in visitor.images().iter() {
             names.push(x.to_path_buf());
         }
@@ -62,31 +61,28 @@ impl Markdown {
     }
 
     /// Find classes used for fenced blocks.
-    pub fn block_classes(&mut self) -> HashSet<String> {
+    pub fn block_classes(&self) -> HashSet<String> {
         let mut visitor = visitor::BlockClassVisitor::default();
-        // Irritatingly we can't immutably visit the AST for some reason
-        // This clone() is expensive and unwanted, but I'm not sure how
-        // to get around it for now
-        visitor.walk_pandoc(self.pandoc());
+        visitor.walk_pandoc(&mut self.pandoc.borrow_mut());
         visitor.classes
     }
 
     /// Typeset.
     pub fn typeset(&mut self, style: Style, bindings: &Bindings) -> Vec<Warning> {
         let mut visitor = visitor::TypesettingVisitor::new(style, bindings);
-        visitor.walk_pandoc(self.pandoc());
+        visitor.walk_pandoc(&mut self.pandoc.borrow_mut());
         visitor.warnings().warnings().to_vec()
     }
 
     /// Find scenarios.
-    pub fn scenarios(&mut self) -> Result<Vec<Scenario>, SubplotError> {
+    pub fn scenarios(&self) -> Result<Vec<Scenario>, SubplotError> {
         trace!(
             "Metadata::scenarios: looking for scenarios: {:#?}",
             self.pandoc
         );
 
         let mut visitor = visitor::StructureVisitor::new();
-        visitor.walk_pandoc(self.pandoc());
+        visitor.walk_pandoc(&mut self.pandoc.borrow_mut());
         trace!(
             "Metadata::scenarios: visitor found {} elements: {:#?}",
             visitor.elements.len(),
@@ -108,9 +104,9 @@ impl Markdown {
     }
 
     /// Find embedded files.
-    pub fn embedded_files(&mut self) -> EmbeddedFiles {
+    pub fn embedded_files(&self) -> EmbeddedFiles {
         let mut files = EmbeddedFiles::default();
-        files.walk_pandoc(self.pandoc());
+        files.walk_pandoc(&mut self.pandoc.borrow_mut());
         files
     }
 }
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