fix off-by-one bug while reading heaptrack files (vercel/turborepo#8101)

### Description

allocations are zero indexed...

### Testing Instructions

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  Give a quick description of steps to test your changes.
-->


Closes PACK-3043

crates/turbopack-trace-server/src/reader/heaptrack.rs

@@ -138,10 +138,7 @@ impl HeaptrackFormat {
                 }
             },
             trace_instruction_pointers: vec![0],
-            allocations: vec![AllocationInfo {
-                size: 0,
-                trace_index: 0,
-            }],
+            allocations: vec![],
             spans: 0,
             collapse_crates: env::var("COLLAPSE_CRATES")
                 .unwrap_or_default()

crates/turbopack-trace-server/src/reader/mod.rs

@@ -20,6 +20,8 @@ use crate::{
     store_container::StoreContainer,
 };
 
+const MIN_INITIAL_REPORT_SIZE: u64 = 100 * 1024 * 1024;
+
 trait TraceFormat {
     fn read(&mut self, buffer: &[u8]) -> Result<usize>;
     fn stats(&self) -> String {
@@ -115,17 +117,7 @@ impl TraceReader {
         let mut format: Option<Box<dyn TraceFormat>> = None;
 
         let mut current_read = 0;
-        let mut initial_read = {
-            if let Ok(pos) = file.seek(SeekFrom::End(0)) {
-                if pos > 100 * 1024 * 1024 {
-                    Some(pos)
-                } else {
-                    None
-                }
-            } else {
-                None
-            }
-        };
+        let mut initial_read = { file.seek(SeekFrom::End(0)).ok() };
         if file.seek(SeekFrom::Start(0)).is_err() {
             return false;
         }
@@ -145,7 +137,9 @@ impl TraceReader {
             match file.read(&mut chunk) {
                 Ok(bytes_read) => {
                     if bytes_read == 0 {
-                        if let Some(value) = self.wait_for_more_data(&mut file, &mut initial_read) {
+                        if let Some(value) =
+                            self.wait_for_more_data(&mut file, &mut initial_read, format.as_deref())
+                        {
                             return value;
                         }
                     } else {
@@ -220,7 +214,9 @@ impl TraceReader {
                 }
                 Err(err) => {
                     if err.kind() == io::ErrorKind::UnexpectedEof {
-                        if let Some(value) = self.wait_for_more_data(&mut file, &mut initial_read) {
+                        if let Some(value) =
+                            self.wait_for_more_data(&mut file, &mut initial_read, format.as_deref())
+                        {
                             return value;
                         }
                     } else {
@@ -237,12 +233,19 @@ impl TraceReader {
         &mut self,
         file: &mut TraceFile,
         initial_read: &mut Option<u64>,
+        format: Option<&dyn TraceFormat>,
     ) -> Option<bool> {
         let Ok(pos) = file.stream_position() else {
             return Some(true);
         };
         if let Some(total) = initial_read.take() {
-            println!("Initial read completed ({} MB)", total / (1024 * 1024),);
+            if let Some(format) = format {
+                let stats = format.stats();
+                println!("{}", stats);
+            }
+            if total > MIN_INITIAL_REPORT_SIZE {
+                println!("Initial read completed ({} MB)", total / (1024 * 1024));
+            }
         }
         thread::sleep(Duration::from_millis(100));
         let Ok(end) = file.seek(SeekFrom::End(0)) else {

crates/turbopack-trace-server/src/viewer.rs

@@ -853,7 +853,7 @@ impl Viewer {
             .collect();
         Update {
             lines,
-            max: current,
+            max: max(1, current),
         }
     }
 }