Tencent/matrix · error

Can't open the template file

Error message

Can't open the template file "%s".

What it means

After locating the template file (tpltname), lemon fopen()s it in "rb" mode; if fopen fails it prints 'Can't open the template file "<name>".' and aborts. Unlike error 306, the file was found but could not actually be opened for reading.

Solutions

1. chmod a+r lempar.c (or the path given via -T) so the invoking user can read it
2. Verify the path is a regular readable file (file lempar.c; ls -l)
3. Re-copy the template from the source tree (matrix-sqlite-lint/src/lemon/lemon-gen/lempar.c)
4. Fix the volume mount/filesystem health if on NFS or a container mount

Example fix

// before
-rw------- lempar.c  # owned by root, build runs as builder
// after
chmod 644 lempar.c

#!/bin/sh
TPL=path/to/lempar.c
[ -f "$TPL" ] && [ -r "$TPL" ] || { echo "template not a readable file: $TPL"; exit 1; }
lemon -T "$TPL" parser.y

When it happens

Trigger: lempar.c exists at the resolved path but lacks read permission for the current user; a dangling symlink or directory named lempar.c passes pathsearch/access checks but fopen fails; the file is deleted between lookup and open; a filesystem error (I/O error, encrypted/unmounted volume).

Common situations: Templates copied into the build with wrong ownership/permissions; NFS or Docker volume mount glitches; passing -T a path that resolves to a directory; race conditions in parallel builds cleaning the template directory.

Understand the failure class

Background: "open() failed", "failed to open file", "cannot create file" — what a file open error means and how to fix it — this error's family across 42 libraries.

Related errors

• Can't open file " ".
• Can't find the parser driver template file
• ---Create directory '<outputFile.getAbsolutePath()>' failed!
• Empty grammar.
• parsing conflicts.

AI-assisted analysis of Tencent/matrix@3b8293bd65 (2026-09-08). Data as JSON: /api/errors/e0f4a11b68474767. Report an issue: GitHub.

Appendix: source

Thrown at matrix/matrix-android/matrix-sqlite-lint/src/lemon/lemon-gen/lemon.c:3010

  }else{
    sprintf(buf,"%s.lt",lemp->filename);
  }
  if( access(buf,004)==0 ){
    tpltname = buf;
  }else if( access(templatename,004)==0 ){
    tpltname = templatename;
  }else{
    tpltname = pathsearch(lemp->argv0,templatename,0);
  }
  if( tpltname==0 ){
    fprintf(stderr,"Can't find the parser driver template file \"%s\".\n",
    templatename);
    lemp->errorcnt++;
    return 0;
  }
  in = fopen(tpltname,"rb");
  if( in==0 ){
    fprintf(stderr,"Can't open the template file \"%s\".\n",templatename);
    lemp->errorcnt++;
    return 0;
  }
  return in;
}

/* Print a #line directive line to the output file. */
PRIVATE void tplt_linedir(out,lineno,filename)
FILE *out;
int lineno;
char *filename;
{
  fprintf(out,"#line %d \"",lineno);
  while( *filename ){
    if( *filename == '\\' ) putc('\\',out);
    putc(*filename,out);
    filename++;
  }

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