[DTrace-devel] [PATCH] lexer: support // comments

Eugene Loh eugene.loh at oracle.com
Wed Jul 23 01:18:16 UTC 2025


1)  s/commens/comment/

2)  Am I doing something wrong with this patch?

$ cat x.d
/*
  *  // is this okay?
  */
BEGIN {
   exit(0);
}

I get stuff like:
         /*/encountered inside a line comment

Frankly, I don't get as far as this script;  I first hit such problems 
with all the copyright notices we have in D files -- that 
"http://oss...." stuff:

/*
  * Oracle Linux DTrace.
  * Copyright (c) 2012, 2023, Oracle and/or its affiliates. All rights 
reserved.
  * Licensed under the Universal Permissive License v 1.0 as shown at
  * http://oss.oracle.com/licenses/upl.
  */

3)  Where do all the rules in this patch (tested by err.*) come from?  
E.g., C seems more lenient:

$ cat x.c
// /* hello */
// comment /*
// comment //
int main(int c, char **v) {
   /*
    * //
    */
   return 0;
}
$ gcc x.c
$ echo $?
0

On 7/22/25 18:12, Kris Van Hees via DTrace-devel wrote:
> Suggested-by: Ruud van der Pas <ruud.vanderpas at oracle.com>
> Suggested-by: Alan Maguire <alan.maguire at oracle.com>
> Signed-off-by: Kris Van Hees <kris.van.hees at oracle.com>
> ---
>   libdtrace/dt_lex.l                               | 14 +++++++++++++-
>   .../lexer/err.D_SYNTAX.boc-in-line-comment.d     | 16 ++++++++++++++++
>   .../lexer/err.D_SYNTAX.boc-in-line-comment.r     |  2 ++
>   .../lexer/err.D_SYNTAX.eoc-in-line-comment.d     | 16 ++++++++++++++++
>   .../lexer/err.D_SYNTAX.eoc-in-line-comment.r     |  2 ++
>   .../lexer/err.D_SYNTAX.eof-in-line-comment.d     | 16 ++++++++++++++++
>   .../lexer/err.D_SYNTAX.eof-in-line-comment.r     |  2 ++
>   .../lexer/err.D_SYNTAX.lc-in-line-comment.d      | 16 ++++++++++++++++
>   .../lexer/err.D_SYNTAX.lc-in-line-comment.r      |  2 ++
>   test/unittest/lexer/tst.line-comment.d           | 16 ++++++++++++++++
>   test/unittest/lexer/tst.line-comment.r           |  5 +++++
>   11 files changed, 106 insertions(+), 1 deletion(-)
>   create mode 100644 test/unittest/lexer/err.D_SYNTAX.boc-in-line-comment.d
>   create mode 100644 test/unittest/lexer/err.D_SYNTAX.boc-in-line-comment.r
>   create mode 100644 test/unittest/lexer/err.D_SYNTAX.eoc-in-line-comment.d
>   create mode 100644 test/unittest/lexer/err.D_SYNTAX.eoc-in-line-comment.r
>   create mode 100644 test/unittest/lexer/err.D_SYNTAX.eof-in-line-comment.d
>   create mode 100644 test/unittest/lexer/err.D_SYNTAX.eof-in-line-comment.r
>   create mode 100644 test/unittest/lexer/err.D_SYNTAX.lc-in-line-comment.d
>   create mode 100644 test/unittest/lexer/err.D_SYNTAX.lc-in-line-comment.r
>   create mode 100644 test/unittest/lexer/tst.line-comment.d
>   create mode 100644 test/unittest/lexer/tst.line-comment.r
>
> diff --git a/libdtrace/dt_lex.l b/libdtrace/dt_lex.l
> index 9d502912..a7234800 100644
> --- a/libdtrace/dt_lex.l
> +++ b/libdtrace/dt_lex.l
> @@ -35,6 +35,7 @@ int yydebug;
>    * S2 - D program outer scope (probe specifiers and declarations)
>    * S3 - D control line parsing (i.e. after ^# is seen but before \n)
>    * S4 - D control line scan (locate control directives only and invoke S3)
> + * S5 - D line comments (i.e. skip everything until end of line)
>    * SIDENT - identifiers and comments only (after -> and .).  (We switch to
>    *          SIDENT only from state S0: changing this would require new code
>    *          to track the state to switch back to.)
> @@ -46,7 +47,7 @@ int yydebug;
>   %n 600		/* maximum states */
>   %option yylineno
>   
> -%s S0 S1 S2 S3 S4 SIDENT
> +%s S0 S1 S2 S3 S4 S5 SIDENT
>   
>   RGX_AGG		"@"[a-zA-Z_][0-9a-zA-Z_]*
>   RGX_PSPEC	[-$:a-zA-Z_.?*\\\[\]!][-$:0-9a-zA-Z_.`?*\\\[\]!]*
> @@ -408,6 +409,11 @@ if (yypcb->pcb_token != 0) {
>   			BEGIN(S1);
>   		}
>   
> +<S0,S2,SIDENT>"//"	{
> +			yypcb->pcb_cstate = (YYSTATE);
> +			BEGIN(S5);
> +		}
> +
>   <S0>^{RGX_INTERP} |
>   <S2>^{RGX_INTERP} ;	/* discard any #! lines */
>   
> @@ -548,6 +554,12 @@ if (yypcb->pcb_token != 0) {
>   <S1>.|\n	; /* discard */
>   <S1><<EOF>>	yyerror("end-of-file encountered before matching */\n");
>   
> +<S1>"/*"	yyerror("/* encountered inside a line comment\n");
> +<S1>"*/"	yyerror("*/ encountered inside a line comment\n");
> +<S1>"//"	yyerror("/*/encountered inside a line comment\n");
> +<S5>\n		BEGIN(yypcb->pcb_cstate);
> +<S5>.		; /* discard */
> +
>   <S2>{RGX_PSPEC}	{
>   			/*
>   			 * S2 has an ambiguity because RGX_PSPEC includes '*'
> diff --git a/test/unittest/lexer/err.D_SYNTAX.boc-in-line-comment.d b/test/unittest/lexer/err.D_SYNTAX.boc-in-line-comment.d
> new file mode 100644
> index 00000000..61f5961f
> --- /dev/null
> +++ b/test/unittest/lexer/err.D_SYNTAX.boc-in-line-comment.d
> @@ -0,0 +1,16 @@
> +/*
> + * Oracle Linux DTrace.
> + * Copyright (c) 2025, Oracle and/or its affiliates. All rights reserved.
> + * Licensed under the Universal Permissive License v 1.0 as shown at
> + * http://oss.oracle.com/licenses/upl.
> + */
> +
> +/*
> + * ASSERTION: Line comments cannot contain begin-of-comment markers.
> + */
> +
> +// Comment /*
> +BEGIN
> +{
> +	exit(0);
> +}
> diff --git a/test/unittest/lexer/err.D_SYNTAX.boc-in-line-comment.r b/test/unittest/lexer/err.D_SYNTAX.boc-in-line-comment.r
> new file mode 100644
> index 00000000..74d1d0ef
> --- /dev/null
> +++ b/test/unittest/lexer/err.D_SYNTAX.boc-in-line-comment.r
> @@ -0,0 +1,2 @@
> +-- @@stderr --
> +dtrace: failed to compile script test/unittest/lexer/err.D_SYNTAX.boc-in-line-comment.d: [D_SYNTAX] line 12: /* encountered inside a line comment
> diff --git a/test/unittest/lexer/err.D_SYNTAX.eoc-in-line-comment.d b/test/unittest/lexer/err.D_SYNTAX.eoc-in-line-comment.d
> new file mode 100644
> index 00000000..8fe2ff04
> --- /dev/null
> +++ b/test/unittest/lexer/err.D_SYNTAX.eoc-in-line-comment.d
> @@ -0,0 +1,16 @@
> +/*
> + * Oracle Linux DTrace.
> + * Copyright (c) 2025, Oracle and/or its affiliates. All rights reserved.
> + * Licensed under the Universal Permissive License v 1.0 as shown at
> + * http://oss.oracle.com/licenses/upl.
> + */
> +
> +/*
> + * ASSERTION: Line comments cannot contain end-of-comment markers.
> + */
> +
> +// Comment */
> +BEGIN
> +{
> +	exit(0);
> +}
> diff --git a/test/unittest/lexer/err.D_SYNTAX.eoc-in-line-comment.r b/test/unittest/lexer/err.D_SYNTAX.eoc-in-line-comment.r
> new file mode 100644
> index 00000000..64d5ae63
> --- /dev/null
> +++ b/test/unittest/lexer/err.D_SYNTAX.eoc-in-line-comment.r
> @@ -0,0 +1,2 @@
> +-- @@stderr --
> +dtrace: failed to compile script test/unittest/lexer/err.D_SYNTAX.eoc-in-line-comment.d: [D_SYNTAX] line 12: */ encountered inside a line comment
> diff --git a/test/unittest/lexer/err.D_SYNTAX.eof-in-line-comment.d b/test/unittest/lexer/err.D_SYNTAX.eof-in-line-comment.d
> new file mode 100644
> index 00000000..a9207693
> --- /dev/null
> +++ b/test/unittest/lexer/err.D_SYNTAX.eof-in-line-comment.d
> @@ -0,0 +1,16 @@
> +/*
> + * Oracle Linux DTrace.
> + * Copyright (c) 2025, Oracle and/or its affiliates. All rights reserved.
> + * Licensed under the Universal Permissive License v 1.0 as shown at
> + * http://oss.oracle.com/licenses/upl.
> + */
> +
> +/*
> + * ASSERTION: End-of-file in a line comment is an error.
> + */
> +
> +BEGIN
> +{
> +	exit(0);
> +}
> +// Comment
> \ No newline at end of file
> diff --git a/test/unittest/lexer/err.D_SYNTAX.eof-in-line-comment.r b/test/unittest/lexer/err.D_SYNTAX.eof-in-line-comment.r
> new file mode 100644
> index 00000000..f46fce3e
> --- /dev/null
> +++ b/test/unittest/lexer/err.D_SYNTAX.eof-in-line-comment.r
> @@ -0,0 +1,2 @@
> +-- @@stderr --
> +dtrace: failed to compile script test/unittest/lexer/err.D_SYNTAX.eof-in-line-comment.d: [D_SYNTAX] line 16: end-of-file encountered in line comment
> diff --git a/test/unittest/lexer/err.D_SYNTAX.lc-in-line-comment.d b/test/unittest/lexer/err.D_SYNTAX.lc-in-line-comment.d
> new file mode 100644
> index 00000000..0332e1ae
> --- /dev/null
> +++ b/test/unittest/lexer/err.D_SYNTAX.lc-in-line-comment.d
> @@ -0,0 +1,16 @@
> +/*
> + * Oracle Linux DTrace.
> + * Copyright (c) 2025, Oracle and/or its affiliates. All rights reserved.
> + * Licensed under the Universal Permissive License v 1.0 as shown at
> + * http://oss.oracle.com/licenses/upl.
> + */
> +
> +/*
> + * ASSERTION: Line comments cannot contain a line commens marker.
> + */
> +
> +// Comment //
> +BEGIN
> +{
> +	exit(0);
> +}
> diff --git a/test/unittest/lexer/err.D_SYNTAX.lc-in-line-comment.r b/test/unittest/lexer/err.D_SYNTAX.lc-in-line-comment.r
> new file mode 100644
> index 00000000..d1152afc
> --- /dev/null
> +++ b/test/unittest/lexer/err.D_SYNTAX.lc-in-line-comment.r
> @@ -0,0 +1,2 @@
> +-- @@stderr --
> +dtrace: failed to compile script test/unittest/lexer/err.D_SYNTAX.lc-in-line-comment.d: [D_SYNTAX] line 12: // encountered inside a line comment
> diff --git a/test/unittest/lexer/tst.line-comment.d b/test/unittest/lexer/tst.line-comment.d
> new file mode 100644
> index 00000000..4deb66f4
> --- /dev/null
> +++ b/test/unittest/lexer/tst.line-comment.d
> @@ -0,0 +1,16 @@
> +/*
> + * Oracle Linux DTrace.
> + * Copyright (c) 2025, Oracle and/or its affiliates. All rights reserved.
> + * Licensed under the Universal Permissive License v 1.0 as shown at
> + * http://oss.oracle.com/licenses/upl.
> + */
> +
> +/*
> + * ASSERTION: // comments are supported.
> + */
> +
> +// exit(1);
> +BEGIN // exit(1);
> +{ // exit(1);
> +	exit(0); // exit(1);
> +} // exit(1);
> diff --git a/test/unittest/lexer/tst.line-comment.r b/test/unittest/lexer/tst.line-comment.r
> new file mode 100644
> index 00000000..d4e4c325
> --- /dev/null
> +++ b/test/unittest/lexer/tst.line-comment.r
> @@ -0,0 +1,5 @@
> +                   FUNCTION:NAME
> +                          :BEGIN
> +
> +-- @@stderr --
> +dtrace: script 'test/unittest/lexer/tst.line-comment.d' matched 1 probe



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