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⚡ Bolt: [String allocation optimization in std.web] #185

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Merged
Tcode-Motion merged 1 commit into from
Sep 22, 2026
Merged

⚡ Bolt: [String allocation optimization in std.web] #185

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3 changes: 3 additions & 0 deletions .jules/bolt.md
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Original file line number Diff line number Diff line change
Expand Up @@ -29,3 +29,6 @@
## 2026-09-20 - String allocation optimization in stdlib json stringify
**Learning:** Generating large JSON structures heavily penalizes performance if intermediate strings are allocated inside loops, specifically using `format!` and joining `Vec<String>`. Converting string builders to pass down a mutable `&mut String` buffer to sub-functions significantly improves performance and reduces heap allocations.
**Action:** Use recursive string builders holding a mutable reference to a `String` inside JSON or tree serialization tasks instead of allocating and returning new `String`s for every sub-node.
## 2026-09-22 - String allocation optimization in std.web DSL rendering
**Learning:** Generating deep HTML structures in `std.web` heavily penalized performance because `dsl_to_html` allocated and returned a new `String` for every child DSL node. This causes `O(N)` heap allocations and redundant copying in the render tree. By passing a mutable `&mut String` buffer recursively downwards, we avoid all intermediate string heap allocations and significantly improve serialization speed.
**Action:** Always prefer using a recursive builder pattern passing a single mutable `&mut String` buffer to `write!` or `push_str` when rendering nested tree structures (like HTML, JSON, or ASTs) instead of returning newly allocated strings at each layer.
240 changes: 124 additions & 116 deletions stdlib/src/web.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -98,9 +98,10 @@ static PAGE_CONTENT: Mutex<String> = Mutex::new(String::new());

fn render_children(html: &mut String, dsl: &techscript_runtime::value::DslBlockValue) {
for child in &dsl.children {
html.push_str(&dsl_to_html(
dsl_to_html_inner(
&techscript_runtime::value::RuntimeValue::DslBlock(std::rc::Rc::new(child.clone())),
));
html,
);
}
}

Expand Down Expand Up @@ -233,129 +234,136 @@ fn render_card(html: &mut String, dsl: &techscript_runtime::value::DslBlockValue

/// Convert a DslBlockValue tree to HTML string.
fn dsl_to_html(val: &RuntimeValue) -> String {
// ⚡ Bolt Performance Optimization:
// This function previously allocated and returned a new String for every single DSL node,
// causing heavy heap allocations when rendering deeply nested HTML structures.
// By passing a single mutable `String` buffer downwards via `dsl_to_html_inner`,
// we eliminate intermediate string heap allocations and significantly improve rendering speed.
let mut html = String::new();
dsl_to_html_inner(val, &mut html);
html
}

fn dsl_to_html_inner(val: &RuntimeValue, html: &mut String) {
match val {
RuntimeValue::DslBlock(dsl) => {
let mut html = String::new();
match dsl.kind.as_str() {
"website" => {
render_website(&mut html, dsl);
}
"page" => {
render_page(&mut html, dsl);
}
"hero" => {
render_hero(&mut html, dsl);
}
"section" => {
render_section(&mut html, dsl);
}
"card" => {
render_card(&mut html, dsl);
}
"button" => {
let label = dsl
.properties
.iter()
.find(|p| p.name == "label")
.and_then(|p| p.value.as_ref())
.map(|v| v.to_string())
.unwrap_or_else(|| "Button".to_string());
let _ = write!(html, "<button>{}</button>", label);
}
"link" => {
let label = dsl
.properties
.iter()
.find(|p| p.name == "label")
.and_then(|p| p.value.as_ref())
.map(|v| v.to_string())
.unwrap_or_else(|| "Link".to_string());
let url = dsl
.properties
.iter()
.find(|p| p.name == "url")
.and_then(|p| p.value.as_ref())
.map(|v| v.to_string());
if let Some(u) = url {
let _ = write!(html, "<a href=\"{}\">{}</a>", u, label);
} else {
let _ = write!(html, "<a href=\"#\">{}</a>", label);
}
}
"nav" => {
html.push_str("<nav>");
render_children(&mut html, dsl);
html.push_str("</nav>");
RuntimeValue::DslBlock(dsl) => match dsl.kind.as_str() {
"website" => {
render_website(html, dsl);
}
"page" => {
render_page(html, dsl);
}
"hero" => {
render_hero(html, dsl);
}
"section" => {
render_section(html, dsl);
}
"card" => {
render_card(html, dsl);
}
"button" => {
let label = dsl
.properties
.iter()
.find(|p| p.name == "label")
.and_then(|p| p.value.as_ref())
.map(|v| v.to_string())
.unwrap_or_else(|| "Button".to_string());
let _ = write!(html, "<button>{}</button>", label);
}
"link" => {
let label = dsl
.properties
.iter()
.find(|p| p.name == "label")
.and_then(|p| p.value.as_ref())
.map(|v| v.to_string())
.unwrap_or_else(|| "Link".to_string());
let url = dsl
.properties
.iter()
.find(|p| p.name == "url")
.and_then(|p| p.value.as_ref())
.map(|v| v.to_string());
if let Some(u) = url {
let _ = write!(html, "<a href=\"{}\">{}</a>", u, label);
} else {
let _ = write!(html, "<a href=\"#\">{}</a>", label);
}
"header" => {
html.push_str("<header>");
for prop in &dsl.properties {
if prop.name == "title" {
if let Some(RuntimeValue::Str(t)) = &prop.value {
let _ = write!(html, "<h1>{}</h1>", t);
}
}
"nav" => {
html.push_str("<nav>");
render_children(html, dsl);
html.push_str("</nav>");
}
"header" => {
html.push_str("<header>");
for prop in &dsl.properties {
if prop.name == "title" {
if let Some(RuntimeValue::Str(t)) = &prop.value {
let _ = write!(html, "<h1>{}</h1>", t);
}
}
render_children(&mut html, dsl);
html.push_str("</header>");
}
"footer" => {
html.push_str("<footer>");
for prop in &dsl.properties {
if prop.name == "text" {
if let Some(RuntimeValue::Str(t)) = &prop.value {
let _ = write!(html, "<p>{}</p>", t);
}
render_children(html, dsl);
html.push_str("</header>");
}
"footer" => {
html.push_str("<footer>");
for prop in &dsl.properties {
if prop.name == "text" {
if let Some(RuntimeValue::Str(t)) = &prop.value {
let _ = write!(html, "<p>{}</p>", t);
}
}
render_children(&mut html, dsl);
html.push_str("</footer>");
}
"input" => {
let placeholder = dsl
.properties
.iter()
.find(|p| p.name == "placeholder")
.and_then(|p| p.value.as_ref())
.map(|v| v.to_string());
if let Some(p) = placeholder {
let _ = write!(html, "<input placeholder=\"{}\">", p);
} else {
html.push_str("<input>");
}
}
"form" => {
html.push_str("<form>");
render_children(&mut html, dsl);
html.push_str("</form>");
}
"main" => {
html.push_str("<main>");
render_children(&mut html, dsl);
html.push_str("</main>");
}
"aside" => {
html.push_str("<aside>");
render_children(&mut html, dsl);
html.push_str("</aside>");
}
"start" => {
let label = dsl
.properties
.iter()
.find(|p| p.name == "label")
.and_then(|p| p.value.as_ref())
.map(|v| v.to_string())
.unwrap_or_else(|| "Get Started".to_string());
let _ = write!(html, "<a class=\"start-button\" href=\"#\">{}</a>", label);
}
_ => {
let _ = write!(html, "<!-- unknown DSL block: {} -->", dsl.kind);
render_children(html, dsl);
html.push_str("</footer>");
}
"input" => {
let placeholder = dsl
.properties
.iter()
.find(|p| p.name == "placeholder")
.and_then(|p| p.value.as_ref())
.map(|v| v.to_string());
if let Some(p) = placeholder {
let _ = write!(html, "<input placeholder=\"{}\">", p);
} else {
html.push_str("<input>");
}
}
html
}
_ => String::new(),
"form" => {
html.push_str("<form>");
render_children(html, dsl);
html.push_str("</form>");
}
"main" => {
html.push_str("<main>");
render_children(html, dsl);
html.push_str("</main>");
}
"aside" => {
html.push_str("<aside>");
render_children(html, dsl);
html.push_str("</aside>");
}
"start" => {
let label = dsl
.properties
.iter()
.find(|p| p.name == "label")
.and_then(|p| p.value.as_ref())
.map(|v| v.to_string())
.unwrap_or_else(|| "Get Started".to_string());
let _ = write!(html, "<a class=\"start-button\" href=\"#\">{}</a>", label);
}
_ => {
let _ = write!(html, "<!-- unknown DSL block: {} -->", dsl.kind);
}
},
_ => {}
}
}

Expand Down Expand Up @@ -582,7 +590,7 @@ impl StdlibRegistry {
};
let mut html = String::new();
for block in &blocks {
html.push_str(&dsl_to_html(block));
dsl_to_html_inner(block, &mut html);
}
Ok(RuntimeValue::Str(html))
},
Expand Down
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