js-source-scopes 0.7.2

use std::ops::Range;

use swc_common::{BytePos, Span};
use swc_ecma_parser::{Parser, StringInput};
use swc_ecma_visit::{swc_ecma_ast as ast, AstNodePath, VisitAstPath, VisitWithAstPath};

use crate::scope_name::{NameComponent, ScopeName};
use crate::Scopes;

pub(crate) use swc_ecma_parser::error::Error as ParseError;

pub fn parse_with_swc(src: &str) -> Result<Scopes, ParseError> {
    let syntax = tracing::trace_span!("parsing source").in_scope(|| {
        let input = StringInput::new(src, BytePos(0), BytePos(src.len() as u32));

        let mut parser = Parser::new(swc_ecma_parser::Syntax::default(), input, None);

        parser.parse_module()
    })?;

    // dbg!(&syntax);

    tracing::trace_span!("extracting scopes").in_scope(|| {
        let mut collector = ScopeCollector::new();

        syntax.visit_children_with_ast_path(&mut collector, &mut Default::default());

        Ok(collector.into_scopes())
    })
}

/// Converts a [`Span`] into a standard [`Range`].
pub(crate) fn convert_span(span: Span) -> Range<u32> {
    span.lo.0..span.hi.0
}

/// The ScopeCollector is responsible for collection function scopes and computing their names.
///
/// SWCs AST is based around the Visitor pattern. In this case our visitor has some
/// method that act on different function-like AST nodes that we are interested in.
/// From there, the node either has a name itself, or we infer its name from the
/// "path" of parents.
/// As a concrete example:
/// `const name = () => {};`
/// 1. The visitors `visit_arrow_expr` function is invoked for the arrow function
///    on the right hand side. Arrow functions by definition do not have a name.
/// 2. We use the "path" to walk up to the VariableDeclarator.
/// 3. That declarator has a binding pattern on the left hand side, which we use
///    to infer the `name` for the anonymous arrow function expression.
struct ScopeCollector {
    scopes: Scopes,
}

impl ScopeCollector {
    fn new() -> Self {
        Self { scopes: vec![] }
    }

    fn into_scopes(self) -> Scopes {
        self.scopes
    }
}

use swc_ecma_visit::AstParentNodeRef as Parent;

impl VisitAstPath for ScopeCollector {
    fn visit_arrow_expr<'ast: 'r, 'r>(
        &mut self,
        node: &'ast ast::ArrowExpr,
        path: &mut AstNodePath<'r>,
    ) {
        let name = infer_name_from_ctx(path);

        self.scopes.push((convert_span(node.span), Some(name)));

        node.visit_children_with_ast_path(self, path);
    }

    fn visit_function<'ast: 'r, 'r>(
        &mut self,
        node: &'ast ast::Function,
        path: &mut AstNodePath<'r>,
    ) {
        let ident = match path.last() {
            Some(Parent::FnDecl(fn_decl, _)) => Some(fn_decl.ident.clone()),
            Some(Parent::FnExpr(fn_expr, _)) => fn_expr.ident.clone(),
            _ => None,
        };
        let name = name_from_ident_or_ctx(ident, path);

        self.scopes.push((convert_span(node.span), Some(name)));

        node.visit_children_with_ast_path(self, path);
    }

    // NOTE: instead of using `visit_constructor` here to find just a class constructor,
    // we want to find the whole class body, as class property definitions are executed as
    // part of the constructor.
    fn visit_class<'ast: 'r, 'r>(&mut self, node: &'ast ast::Class, path: &mut AstNodePath<'r>) {
        let ident = match path.last() {
            Some(Parent::ClassDecl(class_decl, _)) => Some(class_decl.ident.clone()),
            Some(Parent::ClassExpr(class_expr, _)) => class_expr.ident.clone(),
            _ => None,
        };
        let mut name = name_from_ident_or_ctx(ident, path);
        if !name.components.is_empty() {
            name.components.push_front(NameComponent::interp("new "));
        }

        self.scopes.push((convert_span(node.span), Some(name)));

        node.visit_children_with_ast_path(self, path);
    }

    fn visit_getter_prop<'ast: 'r, 'r>(
        &mut self,
        node: &'ast ast::GetterProp,
        path: &mut AstNodePath<'r>,
    ) {
        let mut name = infer_name_from_ctx(path);

        if !name.components.is_empty() {
            name.components.push_back(NameComponent::interp("."));
        }

        name.components.push_back(prop_name_to_component(&node.key));
        name.components.push_front(NameComponent::interp("get "));

        self.scopes.push((convert_span(node.span), Some(name)));

        node.visit_children_with_ast_path(self, path);
    }

    fn visit_setter_prop<'ast: 'r, 'r>(
        &mut self,
        node: &'ast ast::SetterProp,
        path: &mut AstNodePath<'r>,
    ) {
        let mut name = infer_name_from_ctx(path);

        if !name.components.is_empty() {
            name.components.push_back(NameComponent::interp("."));
        }

        name.components.push_back(prop_name_to_component(&node.key));
        name.components.push_front(NameComponent::interp("set "));

        self.scopes.push((convert_span(node.span), Some(name)));

        node.visit_children_with_ast_path(self, path);
    }
}

/// Uses either the provided [`ast::Ident`] or infers the name from the `path`.
fn name_from_ident_or_ctx(ident: Option<ast::Ident>, path: &AstNodePath) -> ScopeName {
    let mut name = infer_name_from_ctx(path);
    if let Some(ident) = ident {
        name.components.pop_back();
        name.components.push_back(NameComponent::ident(ident));
    }

    name
}

/// Tries to infer a name by walking up the path of ancestors.
fn infer_name_from_ctx(path: &AstNodePath) -> ScopeName {
    let mut scope_name = ScopeName::new();
    let mut kind = ast::MethodKind::Method;
    let mut in_object_lit = false;

    fn push_sep(name: &mut ScopeName) {
        if !name.components.is_empty() {
            name.components.push_front(NameComponent::interp("."));
        }
    }

    for parent in path.iter().rev() {
        match parent {
            // These create a new scope. If we reached this, it means we didn’t
            // use any of the other parents properly.
            Parent::Function(..) | Parent::ArrowExpr(..) | Parent::Constructor(..) => {
                if in_object_lit && !scope_name.components.is_empty() {
                    scope_name
                        .components
                        .push_front(NameComponent::interp("<object>."));
                }
                prefix_getters_setters(kind, &mut scope_name);
                return scope_name;
            }

            // A class which is the parent of a method for which we already
            // have part of the name.
            Parent::ClassExpr(class_expr, _) => {
                if let Some(ident) = &class_expr.ident {
                    push_sep(&mut scope_name);
                    scope_name
                        .components
                        .push_front(NameComponent::ident(ident.clone()));
                }
            }
            Parent::ClassDecl(class_decl, _) => {
                push_sep(&mut scope_name);
                scope_name
                    .components
                    .push_front(NameComponent::ident(class_decl.ident.clone()));

                prefix_getters_setters(kind, &mut scope_name);

                return scope_name;
            }

            // An object literal member:
            // `{ $name() ... }`
            Parent::MethodProp(method, _) => {
                push_sep(&mut scope_name);
                scope_name
                    .components
                    .push_front(prop_name_to_component(&method.key));
            }

            // An object literal property:
            // `{ $name: ... }`
            Parent::KeyValueProp(kv, _) => {
                if let Some(ident) = kv.key.as_ident() {
                    push_sep(&mut scope_name);
                    scope_name
                        .components
                        .push_front(NameComponent::ident(ident.clone().into()));
                }
            }

            // A class method:
            // `class { $name() ... }`
            Parent::ClassMethod(method, _) => {
                scope_name
                    .components
                    .push_front(prop_name_to_component(&method.key));

                kind = method.kind;
            }

            // A private class method:
            // `class { #$name() ... }`
            Parent::PrivateMethod(method, _) => {
                scope_name
                    .components
                    .push_front(NameComponent::ident(ast::Ident::new_no_ctxt(
                        method.key.name.clone(),
                        method.key.span,
                    )));
                scope_name.components.push_front(NameComponent::interp("#"));
            }

            // A variable declaration with a name:
            // `var $name = ...`
            Parent::VarDeclarator(decl, _) => {
                if let Some(ident) = decl.name.as_ident() {
                    push_sep(&mut scope_name);
                    scope_name
                        .components
                        .push_front(NameComponent::ident(ident.id.clone()));

                    prefix_getters_setters(kind, &mut scope_name);

                    return scope_name;
                }
            }

            // An assignment expression with a usable name on the left hand side
            // `$name = ...`
            Parent::AssignExpr(expr, _) => match &expr.left {
                ast::AssignTarget::Simple(ast::SimpleAssignTarget::Ident(ident)) => {
                    push_sep(&mut scope_name);
                    scope_name
                        .components
                        .push_front(NameComponent::ident(ident.id.clone()));

                    prefix_getters_setters(kind, &mut scope_name);

                    return scope_name;
                }
                ast::AssignTarget::Simple(ast::SimpleAssignTarget::Member(member)) => {
                    if let Some(mut expr_name) = infer_name_from_expr(&member.obj) {
                        if let Some(ident) = member.prop.as_ident() {
                            scope_name
                                .components
                                .push_front(NameComponent::ident(ident.clone().into()));
                            push_sep(&mut scope_name);
                        }

                        if let Some(computed_prop) = member.prop.as_computed() {
                            push_computed_prop_name(computed_prop, &mut scope_name)
                        }

                        expr_name.components.append(&mut scope_name.components);
                        scope_name.components = expr_name.components;

                        prefix_getters_setters(kind, &mut scope_name);

                        return scope_name;
                    }
                }
                _ => {}
            },

            Parent::ObjectLit(_, _) => {
                in_object_lit = true;
            }

            _ => {}
        }
    }

    if in_object_lit && !scope_name.components.is_empty() {
        scope_name
            .components
            .push_front(NameComponent::interp("<object>."));
    }
    prefix_getters_setters(kind, &mut scope_name);
    scope_name
}

fn prefix_getters_setters(kind: ast::MethodKind, scope_name: &mut ScopeName) {
    match kind {
        ast::MethodKind::Getter => scope_name
            .components
            .push_front(NameComponent::interp("get ")),
        ast::MethodKind::Setter => scope_name
            .components
            .push_front(NameComponent::interp("set ")),
        _ => {}
    }
}

/// Returns a [`ScopeName`] corresponding to the given [`ast::Expr`].
///
/// This is only possible if the expression is an identifier or a member expression.
fn infer_name_from_expr(mut expr: &ast::Expr) -> Option<ScopeName> {
    let mut scope_name = ScopeName::new();

    loop {
        match expr {
            ast::Expr::Ident(ident) => {
                scope_name
                    .components
                    .push_front(NameComponent::ident(ident.clone()));
                return Some(scope_name);
            }

            ast::Expr::Member(member) => {
                if let Some(ident) = member.prop.as_ident() {
                    scope_name
                        .components
                        .push_front(NameComponent::ident(ident.clone().into()));
                    scope_name.components.push_front(NameComponent::interp("."));
                }

                if let Some(computed_prop) = member.prop.as_computed() {
                    push_computed_prop_name(computed_prop, &mut scope_name)
                }

                expr = &member.obj;
            }

            ast::Expr::This(..) => {
                scope_name
                    .components
                    .push_front(NameComponent::interp("this"));
                return Some(scope_name);
            }

            _ => return None,
        }
    }
}

fn push_computed_prop_name(prop_name: &ast::ComputedPropName, scope_name: &mut ScopeName) {
    if let Some(literal) = prop_name.expr.as_lit() {
        let component = NameComponent::interp(format!("[{}]", lit_as_string(literal)));
        scope_name.components.push_front(component);
    } else if let Some(ident) = prop_name.expr.as_ident() {
        scope_name.components.push_front(NameComponent::interp("]"));
        scope_name
            .components
            .push_front(NameComponent::ident(ident.clone()));
        scope_name.components.push_front(NameComponent::interp("["));
    } else {
        scope_name
            .components
            .push_front(NameComponent::interp("[<computed>]"));
    }
}

fn lit_as_string(lit: &ast::Lit) -> String {
    match lit {
        ast::Lit::Str(v) => format!("{:?}", v.value),
        ast::Lit::Num(v) => v.value.to_string(),
        ast::Lit::BigInt(v) => format!("{}n", v.value),
        ast::Lit::Bool(v) => v.value.to_string(),
        ast::Lit::Regex(v) => format!("/{}/{}", v.exp, v.flags),
        ast::Lit::Null(_) => String::from("null"),
        ast::Lit::JSXText(v) => v.value.to_string(),
    }
}

fn prop_name_to_component(prop: &ast::PropName) -> NameComponent {
    match prop {
        ast::PropName::Ident(ref i) => NameComponent::ident(i.clone().into()),
        ast::PropName::Str(s) => NameComponent::interp(format!("<{:?}>", s.value)),
        ast::PropName::Num(n) => NameComponent::interp(format!("<{}>", n)),
        ast::PropName::Computed(_) => NameComponent::interp("<computed>"),
        ast::PropName::BigInt(i) => NameComponent::interp(format!("<{}n>", i.value)),
    }
}