fix(ser): Make pretty actually pretty

This includes porting tests over from `toml-rs` to ensure we match their
behavior.  We removed the non-pretty case and the customization since
those aren't as important for our use case (cargo) and we'll want to
iterate on what we want from the API.

Our "pretty" is different than `toml-rs` in that we prefer `"` for
strings that could be literals but don't need to be literals to avoid
escaping.

Note: there are some other discrepancies in our "pretty" string handling
that should be looked into, like switching to tripple quotes to avoid
escaping.

Fixes #192

src/item.rs

@@ -28,6 +28,7 @@ impl Item {
         self
     }
 }
+
 // TODO: This should be generated by macro or derive
 /// Downcasting
 impl Item {
@@ -128,29 +129,52 @@ impl Item {
     }
     /// In-place convert to a value
     pub fn make_value(&mut self) {
-        let mut other = Item::None;
-        std::mem::swap(self, &mut other);
-        let mut other = other.into_value().map(Item::Value).unwrap_or(Item::None);
-        std::mem::swap(self, &mut other);
+        let other = std::mem::take(self);
+        let other = other.into_value().map(Item::Value).unwrap_or(Item::None);
+        *self = other;
     }
     /// Casts `self` to table.
     pub fn into_table(self) -> Result<Table, Self> {
         match self {
             Item::Table(t) => Ok(t),
-            Item::Value(v) => match v {
-                Value::InlineTable(t) => Ok(t.into_table()),
-                _ => Err(Item::Value(v)),
-            },
+            Item::Value(Value::InlineTable(t)) => Ok(t.into_table()),
             _ => Err(self),
         }
     }
     /// Casts `self` to array of tables.
     pub fn into_array_of_tables(self) -> Result<ArrayOfTables, Self> {
         match self {
             Item::ArrayOfTables(a) => Ok(a),
+            Item::Value(Value::Array(a)) => {
+                if a.is_empty() {
+                    Err(Item::Value(Value::Array(a)))
+                } else if a.iter().all(|v| v.is_inline_table()) {
+                    let mut aot = ArrayOfTables::new();
+                    aot.values = a.values;
+                    for value in aot.values.iter_mut() {
+                        value.make_item();
+                    }
+                    Ok(aot)
+                } else {
+                    Err(Item::Value(Value::Array(a)))
+                }
+            }
             _ => Err(self),
         }
     }
+    // Starting private because the name is unclear
+    pub(crate) fn make_item(&mut self) {
+        let other = std::mem::take(self);
+        let other = match other.into_table().map(crate::Item::Table) {
+            Ok(i) => i,
+            Err(i) => i,
+        };
+        let other = match other.into_array_of_tables().map(crate::Item::ArrayOfTables) {
+            Ok(i) => i,
+            Err(i) => i,
+        };
+        *self = other;
+    }
     /// Returns true iff `self` is a value.
     pub fn is_value(&self) -> bool {
         self.as_value().is_some()

src/ser/mod.rs

@@ -5,13 +5,16 @@
 mod array;
 mod item;
 mod key;
+mod pretty;
 mod table;
 
 pub(crate) use array::*;
 pub(crate) use item::*;
 pub(crate) use key::*;
 pub(crate) use table::*;
 
+use crate::visit_mut::VisitMut;
+
 /// Errors that can occur when deserializing a type.
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct Error {
@@ -146,7 +149,9 @@ pub fn to_string_pretty<T: ?Sized>(value: &T) -> Result<String, Error>
 where
     T: serde::ser::Serialize,
 {
-    to_document(value).map(|e| e.to_string())
+    let mut document = to_document(value)?;
+    pretty::Pretty.visit_document_mut(&mut document);
+    Ok(document.to_string())
 }
 
 /// Serialize the given data structure into a TOML document.

src/ser/pretty.rs

@@ -0,0 +1,56 @@
+pub(crate) struct Pretty;
+
+impl crate::visit_mut::VisitMut for Pretty {
+    fn visit_document_mut(&mut self, node: &mut crate::Document) {
+        crate::visit_mut::visit_document_mut(self, node);
+        if let Some((_, first)) = node.iter_mut().next() {
+            remove_table_prefix(first);
+        }
+    }
+
+    fn visit_item_mut(&mut self, node: &mut crate::Item) {
+        node.make_item();
+
+        crate::visit_mut::visit_item_mut(self, node);
+    }
+
+    fn visit_table_mut(&mut self, node: &mut crate::Table) {
+        node.decor_mut().clear();
+
+        crate::visit_mut::visit_table_mut(self, node);
+    }
+
+    fn visit_value_mut(&mut self, node: &mut crate::Value) {
+        node.decor_mut().clear();
+
+        crate::visit_mut::visit_value_mut(self, node);
+    }
+
+    fn visit_array_mut(&mut self, node: &mut crate::Array) {
+        crate::visit_mut::visit_array_mut(self, node);
+
+        if (0..=1).contains(&node.len()) {
+            node.set_trailing("");
+            node.set_trailing_comma(false);
+        } else {
+            for item in node.iter_mut() {
+                item.decor_mut().set_prefix("\n    ");
+            }
+            node.set_trailing("\n");
+            node.set_trailing_comma(true);
+        }
+    }
+}
+
+fn remove_table_prefix(node: &mut crate::Item) {
+    match node {
+        crate::Item::None => {}
+        crate::Item::Value(_) => {}
+        crate::Item::Table(t) => t.decor_mut().set_prefix(""),
+        crate::Item::ArrayOfTables(a) => {
+            if let Some(first) = a.values.iter_mut().next() {
+                remove_table_prefix(first);
+            }
+        }
+    }
+}

tests/pretty.rs

@@ -0,0 +1,110 @@
+#![cfg(feature = "easy")]
+
+use pretty_assertions::assert_eq;
+
+const PRETTY_STD: &str = r#"[example]
+array = [
+    "item 1",
+    "item 2",
+]
+empty = []
+one = ["one"]
+oneline = "this has no newlines."
+text = """
+this is the first line
+this is the second line
+"""
+"#;
+
+#[test]
+fn pretty_std() {
+    let toml = PRETTY_STD;
+    let value: toml_edit::easy::Value = toml_edit::easy::from_str(toml).unwrap();
+    let result = toml_edit::easy::to_string_pretty(&value).unwrap();
+    println!("EXPECTED:\n{}", toml);
+    println!("\nRESULT:\n{}", result);
+    assert_eq!(toml, &result);
+}
+
+const PRETTY_TRICKY: &str = r##"[example]
+f = "\f"
+glass = """
+Nothing too unusual, except that I can eat glass in:
+- Greek: Μπορώ να φάω σπασμένα γυαλιά χωρίς να πάθω τίποτα. 
+- Polish: Mogę jeść szkło, i mi nie szkodzi. 
+- Hindi: मैं काँच खा सकता हूँ, मुझे उस से कोई पीडा नहीं होती. 
+- Japanese: 私はガラスを食べられます。それは私を傷つけません。 
+"""
+r = "\r"
+r_newline = """
+\r
+"""
+single = "this is a single line but has \"\" cuz it\"s tricky"
+single_tricky = "single line with ''' in it"
+tabs = """
+this is pretty standard
+\texcept for some \ttabs right here
+"""
+text = """
+this is the first line.
+This has a ''' in it and \"\"\" cuz it's tricky yo
+Also ' and \" because why not
+this is the fourth line
+"""
+"##;
+
+#[test]
+fn pretty_tricky() {
+    let toml = PRETTY_TRICKY;
+    let value: toml_edit::easy::Value = toml_edit::easy::from_str(toml).unwrap();
+    let result = toml_edit::easy::to_string_pretty(&value).unwrap();
+    println!("EXPECTED:\n{}", toml);
+    println!("\nRESULT:\n{}", result);
+    assert_eq!(toml, &result);
+}
+
+const PRETTY_TABLE_ARRAY: &str = r##"[[array]]
+key = "foo"
+
+[[array]]
+key = "bar"
+
+[abc]
+doc = "this is a table"
+
+[example]
+single = "this is a single line string"
+"##;
+
+#[test]
+fn pretty_table_array() {
+    let toml = PRETTY_TABLE_ARRAY;
+    let value: toml_edit::easy::Value = toml_edit::easy::from_str(toml).unwrap();
+    let result = toml_edit::easy::to_string_pretty(&value).unwrap();
+    println!("EXPECTED:\n{}", toml);
+    println!("\nRESULT:\n{}", result);
+    assert_eq!(toml, &result);
+}
+
+const TABLE_ARRAY: &str = r##"[[array]]
+key = "foo"
+
+[[array]]
+key = "bar"
+
+[abc]
+doc = "this is a table"
+
+[example]
+single = "this is a single line string"
+"##;
+
+#[test]
+fn table_array() {
+    let toml = TABLE_ARRAY;
+    let value: toml_edit::easy::Value = toml_edit::easy::from_str(toml).unwrap();
+    let result = toml_edit::easy::to_string_pretty(&value).unwrap();
+    println!("EXPECTED:\n{}", toml);
+    println!("\nRESULT:\n{}", result);
+    assert_eq!(toml, &result);
+}

tests/serde.rs

@@ -29,9 +29,15 @@ macro_rules! equivalent {
 
         // Through a string equivalent
         println!("to_string(literal)");
-        assert_eq!(t!(toml_edit::easy::to_string(&literal)), toml.to_string());
+        assert_eq!(
+            t!(toml_edit::easy::to_string_pretty(&literal)),
+            toml.to_string()
+        );
         println!("to_string(toml)");
-        assert_eq!(t!(toml_edit::easy::to_string(&toml)), toml.to_string());
+        assert_eq!(
+            t!(toml_edit::easy::to_string_pretty(&toml)),
+            toml.to_string()
+        );
         println!("literal, from_str(toml)");
         assert_eq!(literal, t!(toml_edit::easy::from_str(&toml.to_string())));
         println!("toml, from_str(toml)");