Fix sourcemap

Author: hyf0

examples/source_map.rs

@@ -1,16 +1,15 @@
 use string_wizard::{MagicString, SourceMapOptions, UpdateOptions};
 
 fn main() {
-    let demo = "<div>
-    hello, world
-</div>";
+    let demo = "<div>\n  hello, world\n</div>";
     let mut s = MagicString::new(demo);
 
     let update_options = UpdateOptions {
         store_name: true,
         ..Default::default()
     };
-    s.update_with(1, 2, "v", update_options.clone())
+    s.prepend("import React from 'react';\n")
+        .update_with(1, 2, "v", update_options.clone())
         .update_with(3, 4, "d", update_options.clone())
         .update_with(demo.len() - 4, demo.len() - 1, "h1", update_options.clone());
 

src/mappings.rs

@@ -54,24 +54,25 @@ impl Mappings {
             let chunk_content = chunk.span.text(source);
             let mut new_line = true;
             for char in chunk_content.chars() {
-                if new_line {
-                    new_line = false;
-                    let segment = Segment {
-                        dst_column: self.generated_code_column.into(),
-                        source_index: source_index.into(),
-                        src_line: loc.line.into(),
-                        src_column: loc.column.into(),
-                        name_index: None,
-                    };
-                    self.add_segment_to_current_line(segment);
-                }
                 match char {
                     '\n' => {
                         loc.bump_line();
                         self.bump_line();
                         new_line = true;
                     }
                     _ => {
+                        if new_line {
+                            new_line = false;
+                            let segment = Segment {
+                                dst_column: self.generated_code_column.into(),
+                                source_index: source_index.into(),
+                                src_line: loc.line.into(),
+                                src_column: loc.column.into(),
+                                name_index: None,
+                            };
+                            self.add_segment_to_current_line(segment);
+                        }
+
                         let char_utf16_len = char.len_utf16() as u32;
                         loc.column += char_utf16_len;
                         self.generated_code_column += char_utf16_len;
@@ -85,9 +86,11 @@ impl Mappings {
         if content.is_empty() {
             return;
         }
-        let mut lines = content.lines();
-        // SAFETY: The content at least has one line after checking of `content.is_empty()` .
-        // `"\n".lines().collect::<Vec<_>>()` would create `[""]`.
+        let mut lines = content.split('\n');
+        
+        // SAFETY: In any cases, lines would have at least one element.
+        // "".split('\n') would create `[""]`.
+        // "\n".split('\n') would create `["", ""]`.
         let last_line = unsafe { lines.next_back().unwrap_unchecked() };
         for _ in lines {
             self.bump_line();

tests/magic_string_source_map.rs

@@ -10,11 +10,28 @@ fn basic() {
     };
     s.update_with(1, 2, "v", update_options.clone())
         .update_with(3, 4, "d", update_options.clone())
-        .update_with(input.len() - 4, input.len() - 1, "h1", update_options.clone());
+        .update_with(
+            input.len() - 4,
+            input.len() - 1,
+            "h1",
+            update_options.clone(),
+        );
 
     let sm = s.source_map(SourceMapOptions {
         include_content: true,
     });
 
-    assert_eq!(sm.mappings, "AAAA,CAACA,CAAC,CAACC,CAAC;AACJ;AACA,EAAEC,EAAG")
+    assert_eq!(
+        sm.mappings,
+        "AAAA,CAACA,CAAC,CAACC,CAAC;AACJ;AACA,EAAEC,EAAG"
+    );
+
+    s.prepend("import React from 'react';\n");
+    let sm = s.source_map(SourceMapOptions {
+        include_content: true,
+    });
+    assert_eq!(
+        sm.mappings,
+        ";AAAA,CAACA,CAAC,CAACC,CAAC;AACJ;AACA,EAAEC,EAAG"
+    );
 }