Introduce syntax for inserting string_builder values

CHANGELOG.md

@@ -1,10 +1,20 @@
 # Changelog
 
+## Unreleased
+
+- Added support for '{[ name ]}' syntax to allow for inserting string builder values into the
+  template using the underlying `append_builder` call instead of the `append` functon that we use
+  for strings.
+
+  Thank you to @michallepicki for the suggestion.
+
 ## 0.6.0
 
 - Added support for 'for .. as .. in ..' syntax to allow associating a type with the items in the
   list being iterated.
 
+  Thank you to @lpil for the suggestion.
+
 ## 0.5.0
 
 - Added --version flag to executable to print out current version.

README.md

@@ -44,15 +44,29 @@ Alpha. The error messages are poor and there will be plenty of flaws and oversig
 
 The syntax is inspired by [Jinja](https://jinja.palletsprojects.com/).
 
-### Value
+### String Value
 
-You can use `{{ name }}` syntax to insert the value of name into the rendered template. The
+You can use `{{ name }}` syntax to insert the value of `name` into the rendered template. The
 function generated from the template will have a labelled argument matching the identifier used.
 
 ```jinja
 {{ name }}
 ```
 
+### String Builder Value
+
+You can use `{[ name ]}` syntax to insert a string builder value into the rendered template. This
+has the advantage of using
+[string_builder.append_builder](https://hexdocs.pm/gleam_stdlib/gleam/string_builder.html#append_builder)
+in the rendered template and so it more efficient for inserting content that is already in a
+`string_builder`. This can be used to insert content from another template.
+
+The function generated from the template will have a labelled argument matching the identifier used.
+
+```jinja
+{[ name ]}
+```
+
 ### If
 
 You can use `{% %}` blocks to create an if-statement using the `if`, `else` and `endif` keywords.

src/main.rs

@@ -37,6 +37,8 @@ enum Token {
     CloseLine,
     OpenValue,
     CloseValue,
+    OpenBuilder,
+    CloseBuilder,
     Identifier(String),
     Import,
     ImportDetails(String),
@@ -60,6 +62,8 @@ impl std::fmt::Display for Token {
             Token::CloseLine => "\n",
             Token::OpenValue => "{{",
             Token::CloseValue => "}}",
+            Token::OpenBuilder => "{[",
+            Token::CloseBuilder => "]}",
             Token::OpenStmt => "{%",
             Token::CloseStmt => "%}",
             Token::Identifier(name) => name,
@@ -146,6 +150,29 @@ fn scan_plain(iter: &mut Iter, mut tokens: Tokens) -> Result<Tokens, ScanError>
                     ));
                     iter.next();
 
+                    tokens = scan_identifiers(iter, tokens)?;
+                } else if let Some((second_index, "[")) = iter.peek() {
+                    if !buffer.is_empty() {
+                        tokens.push((
+                            Token::Text(buffer),
+                            Range {
+                                start: buffer_start_index.unwrap_or(0),
+                                end: first_index,
+                            },
+                        ));
+                        buffer = String::new();
+                    }
+
+                    tokens.push((
+                        Token::OpenBuilder,
+                        Range {
+                            start: first_index,
+                            end: *second_index,
+                        },
+                    ));
+
+                    iter.next();
+
                     tokens = scan_identifiers(iter, tokens)?;
                 } else if let Some((second_index, ">")) = iter.peek() {
                     tokens.push((
@@ -195,6 +222,21 @@ fn scan_plain(iter: &mut Iter, mut tokens: Tokens) -> Result<Tokens, ScanError>
                     buffer.push('%');
                 }
             }
+            Some((first_index, "]")) => {
+                if let Some((second_index, "}")) = iter.peek() {
+                    tokens.push((
+                        Token::CloseBuilder,
+                        Range {
+                            start: first_index,
+                            end: *second_index,
+                        },
+                    ));
+                    buffer_start_index = None;
+                    iter.next();
+                } else {
+                    buffer.push(']');
+                }
+            }
             Some((index, grapheme)) => {
                 buffer.push_str(grapheme);
                 buffer_start_index = buffer_start_index.or(Some(index));
@@ -220,7 +262,8 @@ fn scan_identifiers(iter: &mut Iter, mut tokens: Tokens) -> Result<Tokens, ScanE
     log::trace!("scan_identifiers");
     loop {
         match iter.peek() {
-            Some((_index, "}")) | Some((_index, "%")) | Some((_index, "\n")) => {
+            Some((_index, "}")) | Some((_index, "%")) | Some((_index, "]"))
+            | Some((_index, "\n")) => {
                 break;
             }
             None => break,
@@ -245,7 +288,7 @@ fn scan_identifier_or_keyword(iter: &mut Iter) -> (Token, Range) {
     loop {
         match iter.peek() {
             Some((_index, "}")) | Some((_index, " ")) | Some((_index, "\n"))
-            | Some((_index, "%")) => {
+            | Some((_index, "%")) | Some((_index, "]")) => {
                 break;
             }
             Some((index, grapheme)) => {
@@ -369,6 +412,7 @@ type Type = String;
 enum Node {
     Text(String),
     Identifier(String),
+    Builder(String),
     If(String, Vec<Node>, Vec<Node>),
     For(String, Option<Type>, String, Vec<Node>),
     Import(String),
@@ -413,6 +457,11 @@ fn parse_inner(tokens: &mut TokenIter, in_statement: bool) -> Result<Vec<Node>,
                 ast.push(Node::Identifier(name.clone()));
                 consume_token(tokens, Token::CloseValue)?;
             }
+            Some((Token::OpenBuilder, _)) => {
+                let name = extract_identifier(tokens)?;
+                ast.push(Node::Builder(name.clone()));
+                consume_token(tokens, Token::CloseBuilder)?;
+            }
             Some((Token::OpenStmt, _)) => {
                 if let Some((Token::Else, _)) | Some((Token::EndIf, _)) | Some((Token::EndFor, _)) =
                     tokens.peek()
@@ -661,6 +710,14 @@ fn render_lines(
                 ));
                 params.push(name.clone());
             }
+            Some(Node::Builder(name)) => {
+                iter.next();
+                builder_lines.push_str(&format!(
+                    "    let builder = string_builder.append_builder(builder, {})\n",
+                    name
+                ));
+                params.push(name.clone());
+            }
             Some(Node::Import(import_details)) => {
                 iter.next();
                 imports.push(import_details.clone());
@@ -1063,6 +1120,11 @@ mod test {
         assert_scan!("{> with user as User\n{{ user }}");
     }
 
+    #[test]
+    fn test_scan_builder_block() {
+        assert_scan!("Hello {[ builder ]}, good to meet you");
+    }
+
     // Parse
 
     #[test]
@@ -1134,6 +1196,11 @@ mod test {
         assert_parse!("{> with user as User\n{{ user }}");
     }
 
+    #[test]
+    fn test_parse_builder_block() {
+        assert_parse!("Hello {[ name ]}, good to meet you");
+    }
+
     // Render
 
     #[test]
@@ -1226,6 +1293,11 @@ mod test {
         assert_render!(r#"<div class="my-class">{{ name }}</div>"#);
     }
 
+    #[test]
+    fn test_render_builder_block() {
+        assert_render!("Hello {[ name ]}, good to meet you");
+    }
+
     // Errors
 
     #[test]

src/snapshots/templates__test__parse_builder_block.snap

@@ -0,0 +1,17 @@
+---
+source: src/main.rs
+assertion_line: 1201
+expression: "Hello {[ name ]}, good to meet you"
+
+---
+[
+    Text(
+        "Hello ",
+    ),
+    Builder(
+        "name",
+    ),
+    Text(
+        ", good to meet you",
+    ),
+]

src/snapshots/templates__test__render_builder_block.snap

@@ -0,0 +1,24 @@
+---
+source: src/main.rs
+assertion_line: 1298
+expression: "Hello {[ name ]}, good to meet you"
+
+---
+import gleam/string_builder.{StringBuilder}
+import gleam/list
+
+
+
+pub fn render_builder(name name) -> StringBuilder {
+    let builder = string_builder.from_string("")
+    let builder = string_builder.append(builder, "Hello ")
+    let builder = string_builder.append_builder(builder, name)
+    let builder = string_builder.append(builder, ", good to meet you")
+
+    builder
+}
+
+pub fn render(name name) -> String {
+    string_builder.to_string(render_builder(name: name))
+}
+

src/snapshots/templates__test__scan_builder_block.snap

@@ -0,0 +1,34 @@
+---
+source: src/main.rs
+assertion_line: 1092
+expression: "Hello {[ builder ]}, good to meet you"
+
+---
+[
+    (
+        Text(
+            "Hello ",
+        ),
+        0..6,
+    ),
+    (
+        OpenBuilder,
+        6..7,
+    ),
+    (
+        Identifier(
+            "builder",
+        ),
+        9..16,
+    ),
+    (
+        CloseBuilder,
+        17..18,
+    ),
+    (
+        Text(
+            ", good to meet you",
+        ),
+        19..36,
+    ),
+]

test/template/builder.gleamx

@@ -0,0 +1 @@
+Hello {[ name_builder ]}, good to meet you

test/templates_test.gleam

@@ -1,3 +1,5 @@
+import gleam/string_builder
+
 import gleeunit
 import gleeunit/should
 
@@ -14,6 +16,7 @@ import template/multiline
 import template/value_in_for_loop
 import template/value_in_if_else
 import template/quote
+import template/builder
 
 import my_user.{User, NamedUser}
 
@@ -42,6 +45,12 @@ pub fn double_identifier_usage_test() {
   |> should.equal("Double usage, Double usage\n")
 }
 
+pub fn builder_block_test() {
+  let name_builder = string_builder.from_strings(["Anna", " ", "Bandana"])
+  builder.render(name_builder)
+  |> should.equal("Hello Anna Bandana, good to meet you\n")
+}
+
 pub fn if_statement_test() {
   if_statement.render(True)
   |> should.equal("Hello User\n")