Auto merge of #132791 - tyilo:big-file-fail-fast, r=compiler-errors

rustc: Fail fast when compiling a source file larger than 4 GiB

Currently if you try to compile a file that is larger than 4 GiB, `rustc` will first read the whole into memory before failing.

If we can read the metadata of the file, we can fail before reading the file.

compiler/rustc_span/src/lib.rs

@@ -1829,6 +1829,8 @@ impl StableSourceFileId {
 }
 
 impl SourceFile {
+    const MAX_FILE_SIZE: u32 = u32::MAX - 1;
+
     pub fn new(
         name: FileName,
         mut src: String,
@@ -1849,6 +1851,9 @@ impl SourceFile {
         let stable_id = StableSourceFileId::from_filename_in_current_crate(&name);
         let source_len = src.len();
         let source_len = u32::try_from(source_len).map_err(|_| OffsetOverflowError)?;
+        if source_len > Self::MAX_FILE_SIZE {
+            return Err(OffsetOverflowError);
+        }
 
         let (lines, multibyte_chars) = analyze_source_file::analyze_source_file(&src);
 

compiler/rustc_span/src/source_map.rs

@@ -115,6 +115,12 @@ impl FileLoader for RealFileLoader {
     }
 
     fn read_file(&self, path: &Path) -> io::Result<String> {
+        if path.metadata().is_ok_and(|metadata| metadata.len() > SourceFile::MAX_FILE_SIZE.into()) {
+            return Err(io::Error::other(format!(
+                "text files larger than {} bytes are unsupported",
+                SourceFile::MAX_FILE_SIZE
+            )));
+        }
         fs::read_to_string(path)
     }
 
@@ -297,7 +303,10 @@ impl SourceMap {
     /// unmodified.
     pub fn new_source_file(&self, filename: FileName, src: String) -> Lrc<SourceFile> {
         self.try_new_source_file(filename, src).unwrap_or_else(|OffsetOverflowError| {
-            eprintln!("fatal error: rustc does not support files larger than 4GB");
+            eprintln!(
+                "fatal error: rustc does not support text files larger than {} bytes",
+                SourceFile::MAX_FILE_SIZE
+            );
             crate::fatal_error::FatalError.raise()
         })
     }