feat: allow specifying a base for source maps (#262)

src/emit.rs

@@ -10,6 +10,7 @@ use crate::swc::ast::Program;
 use crate::swc::codegen::text_writer::JsWriter;
 use crate::swc::codegen::Node;
 use crate::swc::common::FileName;
+use crate::ModuleSpecifier;
 use crate::SourceMap;
 
 #[derive(Default, Debug, Clone, Copy, PartialEq, Eq, Hash)]
@@ -27,6 +28,11 @@ pub enum SourceMapOption {
 pub struct EmitOptions {
   /// How and if source maps should be generated.
   pub source_map: SourceMapOption,
+  /// Base url to use for source maps.
+  ///
+  /// When a base is provided, when mapping source names in the source map, the
+  /// name will be relative to the base.
+  pub source_map_base: Option<ModuleSpecifier>,
   /// The `"file"` field of the generated source map.
   pub source_map_file: Option<String>,
   /// Whether to inline the source contents in the source map. Defaults to `true`.
@@ -39,6 +45,7 @@ impl Default for EmitOptions {
   fn default() -> Self {
     EmitOptions {
       source_map: SourceMapOption::default(),
+      source_map_base: None,
       source_map_file: None,
       inline_sources: true,
       remove_comments: false,
@@ -122,6 +129,7 @@ pub fn emit(
     let mut map_buf = Vec::new();
     let source_map_config = SourceMapConfig {
       inline_sources: emit_options.inline_sources,
+      maybe_base: emit_options.source_map_base.as_ref(),
     };
     let mut source_map = source_map.build_source_map_with_config(
       &src_map_buf,
@@ -169,13 +177,29 @@ pub fn emit(
 /// Implements a configuration trait for source maps that reflects the logic
 /// to embed sources in the source map or not.
 #[derive(Debug)]
-pub struct SourceMapConfig {
+pub struct SourceMapConfig<'a> {
   pub inline_sources: bool,
+  pub maybe_base: Option<&'a ModuleSpecifier>,
 }
 
-impl crate::swc::common::source_map::SourceMapGenConfig for SourceMapConfig {
+impl<'a> crate::swc::common::source_map::SourceMapGenConfig
+  for SourceMapConfig<'a>
+{
   fn file_name_to_source(&self, f: &FileName) -> String {
-    f.to_string()
+    match f {
+      FileName::Url(specifier) => self
+        .maybe_base
+        .and_then(|base| {
+          debug_assert!(
+            base.as_str().ends_with('/'),
+            "source map base should end with a slash"
+          );
+          base.make_relative(specifier)
+        })
+        .filter(|relative| !relative.is_empty())
+        .unwrap_or_else(|| f.to_string()),
+      _ => f.to_string(),
+    }
   }
 
   fn inline_sources_content(&self, f: &FileName) -> bool {
@@ -193,10 +217,11 @@ pub fn swc_codegen_config() -> crate::swc::codegen::Config {
   // inspect the struct on swc upgrade and explicitly specify any
   // new options here in order to ensure we maintain these settings.
   let mut config = crate::swc::codegen::Config::default();
-  config.minify = false;
+  config.target = crate::ES_VERSION;
   config.ascii_only = false;
+  config.minify = false;
   config.omit_last_semi = false;
-  config.target = crate::ES_VERSION;
   config.emit_assert_for_import_attributes = false;
+  config.inline_script = false;
   config
 }

src/transpiling/mod.rs

@@ -1608,6 +1608,91 @@ const a = _jsx(Foo, {
     );
   }
 
+  #[test]
+  fn test_source_map_base() {
+    #[track_caller]
+    fn run_test(file_name: &str, base: &str, expected: &str) {
+      let specifier = ModuleSpecifier::parse(file_name).unwrap();
+      let source = r#"{ const foo = "bar"; };"#;
+      let module = parse_module(ParseParams {
+        specifier,
+        text: source.into(),
+        media_type: MediaType::Tsx,
+        capture_tokens: false,
+        maybe_syntax: None,
+        scope_analysis: false,
+      })
+      .unwrap();
+      let emit_options = EmitOptions {
+        source_map: SourceMapOption::Separate,
+        source_map_base: Some(ModuleSpecifier::parse(base).unwrap()),
+        ..Default::default()
+      };
+      let emit_result = module
+        .transpile(&TranspileOptions::default(), &emit_options)
+        .unwrap()
+        .into_source()
+        .into_string()
+        .unwrap();
+      assert_eq!(
+        &emit_result.text,
+        r#"{
+  const foo = "bar";
+}"#
+      );
+      let value: serde_json::Value =
+        serde_json::from_str(&emit_result.source_map.unwrap()).unwrap();
+      assert_eq!(
+        value,
+        serde_json::json!({
+          "version":3,
+          "sources":[expected],
+          "sourcesContent":["{ const foo = \"bar\"; };"],
+          "names":[],
+          "mappings":"AAAA;EAAE,MAAM,MAAM;AAAO"
+        })
+      );
+    }
+
+    run_test(
+      "https://deno.land/x/mod.tsx",
+      "https://deno.land/x/",
+      "mod.tsx",
+    );
+    run_test(
+      "https://deno.land/x/mod.tsx",
+      "https://deno.land/",
+      "x/mod.tsx",
+    );
+    run_test(
+      "https://deno.land/x/mod.tsx",
+      "file:///home/user/",
+      "https://deno.land/x/mod.tsx",
+    );
+    run_test(
+      "https://deno.land/x/mod.tsx",
+      "https://example.com/",
+      "https://deno.land/x/mod.tsx",
+    );
+    run_test(
+      "https://example.com/base/",
+      "https://example.com/base/",
+      // maybe not ideal, but this is ok
+      "https://example.com/base/",
+    );
+    run_test("file:///example.ts", "file:///", "example.ts");
+    run_test(
+      "file:///sub_dir/example.ts",
+      "file:///",
+      "sub_dir/example.ts",
+    );
+    run_test(
+      "file:///sub_dir/example.ts",
+      "file:///sub_dir/",
+      "example.ts",
+    );
+  }
+
   #[test]
   fn test_source_map_with_file() {
     let specifier =