fix: Correctly interpret missing line/column numbers (#129)

This correctly interprets sourcemap tokens that only have a minified column number as "unmapped". Previously, such tokens would inherit the source line and column numbers from the last valid token, but that is incorrect. Now we set the numbers to u32::MAX for such cases.

Author: loewenheim

src/decoder.rs

@@ -148,10 +148,13 @@ fn decode_rmi(rmi_str: &str, val: &mut BitVec<u8, Lsb0>) -> Result<()> {
 
 pub fn decode_regular(rsm: RawSourceMap) -> Result<SourceMap> {
     let mut dst_col;
-    let mut src_id = 0;
-    let mut src_line = 0;
-    let mut src_col = 0;
-    let mut name_id = 0;
+
+    // Source IDs, lines, columns, and names are "running" values.
+    // Each token (except the first) contains the delta from the previous value.
+    let mut running_src_id = 0;
+    let mut running_src_line = 0;
+    let mut running_src_col = 0;
+    let mut running_name_id = 0;
 
     let names = rsm.names.unwrap_or_default();
     let sources = rsm.sources.unwrap_or_default();
@@ -183,30 +186,41 @@ pub fn decode_regular(rsm: RawSourceMap) -> Result<SourceMap> {
 
             nums.clear();
             parse_vlq_segment_into(segment, &mut nums)?;
+            match nums.len() {
+                1 | 4 | 5 => {}
+                _ => return Err(Error::BadSegmentSize(nums.len() as u32)),
+            }
+
             dst_col = (i64::from(dst_col) + nums[0]) as u32;
 
-            let mut src = !0;
-            let mut name = !0;
+            // The source file , source line, source column, and name
+            // may not be present in the current token. We use `u32::MAX`
+            // as the placeholder for missing values.
+            let mut current_src_id = !0;
+            let mut current_src_line = !0;
+            let mut current_src_col = !0;
+            let mut current_name_id = !0;
 
             if nums.len() > 1 {
-                if nums.len() != 4 && nums.len() != 5 {
-                    return Err(Error::BadSegmentSize(nums.len() as u32));
-                }
-                src_id = (i64::from(src_id) + nums[1]) as u32;
-                if src_id >= sources.len() as u32 {
-                    return Err(Error::BadSourceReference(src_id));
+                running_src_id = (i64::from(running_src_id) + nums[1]) as u32;
+
+                if running_src_id >= sources.len() as u32 {
+                    return Err(Error::BadSourceReference(running_src_id));
                 }
 
-                src = src_id;
-                src_line = (i64::from(src_line) + nums[2]) as u32;
-                src_col = (i64::from(src_col) + nums[3]) as u32;
+                running_src_line = (i64::from(running_src_line) + nums[2]) as u32;
+                running_src_col = (i64::from(running_src_col) + nums[3]) as u32;
+
+                current_src_id = running_src_id;
+                current_src_line = running_src_line;
+                current_src_col = running_src_col;
 
                 if nums.len() > 4 {
-                    name_id = (i64::from(name_id) + nums[4]) as u32;
-                    if name_id >= names.len() as u32 {
-                        return Err(Error::BadNameReference(name_id));
+                    running_name_id = (i64::from(running_name_id) + nums[4]) as u32;
+                    if running_name_id >= names.len() as u32 {
+                        return Err(Error::BadNameReference(running_name_id));
                     }
-                    name = name_id;
+                    current_name_id = running_name_id;
                 }
             }
 
@@ -215,10 +229,10 @@ pub fn decode_regular(rsm: RawSourceMap) -> Result<SourceMap> {
             tokens.push(RawToken {
                 dst_line: dst_line as u32,
                 dst_col,
-                src_line,
-                src_col,
-                src_id: src,
-                name_id: name,
+                src_line: current_src_line,
+                src_col: current_src_col,
+                src_id: current_src_id,
+                name_id: current_name_id,
                 is_range,
             });
         }

src/types.rs

@@ -242,12 +242,18 @@ impl<'a> Token<'a> {
         (self.get_dst_line(), self.get_dst_col())
     }
 
-    /// get the source line number
+    /// Get the source line number.
+    ///
+    /// `u32::MAX` is a sentinel value meaning
+    /// this token is unmapped.
     pub fn get_src_line(&self) -> u32 {
         self.raw.src_line
     }
 
-    /// get the source column number
+    /// Get the source column number.
+    ///
+    /// `u32::MAX` is a sentinel value meaning
+    /// this token is unmapped.
     pub fn get_src_col(&self) -> u32 {
         self.raw.src_col.saturating_add(self.offset)
     }