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support os.File.WriteString #1554

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Merged
xushiwei merged 1 commit into from
Jan 14, 2026
Merged

support os.File.WriteString #1554

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35 changes: 35 additions & 0 deletions _demo/go/oswritestring/main.go
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Original file line number Diff line number Diff line change
@@ -0,0 +1,35 @@
package main

import (
"fmt"
"os"
)

func main() {
f, err := os.CreateTemp("", "llgo-writestring-*.txt")
if err != nil {
panic(err)
}
Comment on lines +9 to +12
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@gemini-code-assist gemini-code-assist bot Jan 14, 2026

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medium

While using panic is acceptable for a simple demo, it's generally better to use log.Fatalf for handling expected errors like I/O failures. This provides a cleaner error message without a full stack trace, which is more idiomatic for command-line applications and tests.

I'd recommend replacing all panic calls in this file with log.Fatalf. For example, this block could be changed to:

	if err != nil {
		log.Fatalf("Failed to create temp file: %v", err)
	}

This would require adding "log" to the imports.

defer os.Remove(f.Name())

const content = "hello writestring"
if n, err := f.WriteString(content); err != nil {
panic(err)
} else if n != len(content) {
panic(fmt.Sprintf("WriteString wrote %d bytes, want %d", n, len(content)))
}

if err := f.Close(); err != nil {
panic(err)
}

data, err := os.ReadFile(f.Name())
if err != nil {
panic(err)
}
if string(data) != content {
panic(fmt.Sprintf("content mismatch: got %q, want %q", string(data), content))
}

fmt.Println("ok")
}
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@xgopilot xgopilot bot Jan 14, 2026

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The demo validates the happy path well. For more robust testing, consider adding cases for:

  • Empty string: f.WriteString("")
  • Multiple consecutive writes to verify behavior
  • Large strings (e.g., strings.Repeat("x", 10*1024*1024))

This would provide better confidence in edge case handling, especially since this enables previously disabled functionality.

8 changes: 3 additions & 5 deletions runtime/internal/lib/os/file.go
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Original file line number Diff line number Diff line change
Expand Up @@ -9,6 +9,7 @@ import (
"io"
"syscall"
"time"
"unsafe"
)

// Name returns the name of the file as presented to Open.
Expand Down Expand Up @@ -201,11 +202,8 @@ func (f *File) Seek(offset int64, whence int) (ret int64, err error) {
// WriteString is like Write, but writes the contents of string s rather than
// a slice of bytes.
func (f *File) WriteString(s string) (n int, err error) {
/*
b := unsafe.Slice(unsafe.StringData(s), len(s))
return f.Write(b)
*/
panic("todo: os.(*File).WriteString")
b := unsafe.Slice(unsafe.StringData(s), len(s))
return f.Write(b)
}

// Open opens the named file for reading. If successful, methods on
Expand Down
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