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Re: [PATCH v2 1/6] * expand.c (variable_name_extract): extract variable

From: Macpaul Lin
Subject: Re: [PATCH v2 1/6] * expand.c (variable_name_extract): extract variable name and strip prefix.
Date: Thu, 21 Aug 2014 15:25:55 +0800

Hi, Paul and other developers,

2014-08-18 22:35 GMT+08:00 Paul Smith <address@hidden>:
> On Mon, 2014-08-18 at 21:27 +0800, Macpaul Lin wrote:
>> Variables used in conditional lines usually has '$',
>> '(', and ')' prefix, and etc.
>> We can use vairable_name_extract() to extract pure variable
>> name without these prefix.
> Hello.  Thanks for your work on GNU make!
> Can you provide some sort of summary of the feature you've created, what
> its goals are, examples, etc.?
> It can be helpful to contact me or someone on the development team
> before (or while) doing feature work for GNU make.  As a GNU project,
> for example, we'll need to get copyright assignment paperwork for any
> contribution of significant size and this takes some time.
> Also, we may have suggestions or alternative implementations or concerns
> that should be considered.  Of course these can always be addressed
> later, but it can save some effort to think about them up-front.
> And finally, note that fully-formed changes need to have at least a stab
> at changes to the manual (I usually rework these but it's helpful to
> have a starting point) and some additions to the regression test suite,
> if possible.
> Cheers!

It's very happy to receive your response!
Any kind of paperwork of copyright assigment is okay!
Sure, alternative implementations or any other concenrs need to be discussed.
GNU tools are widely delopyed and used in every single second.
I hope the patches could help people instead of bring them disasters.

About the paperwork, because I'm living oudside of U.S. If it can be done by
email or fax is good. If postmail is necessary will be okay, too. Just take
longer round trip time of these documentations.

The following is the description of the purpose of these patches.

* expand.c (variable_name_extract): extract variable name and strip prefix.
* variable.h: Add support of struct value_records and parent_records
* variable.c: Add support for constructing value_records and parent_records
* read.c: Construct the dependency chain between parent and target variable
* load.c: add support of parent_records
* main.c: add --dep parameter for print variable dependency

This set of patches were created to help developers to understand
the dependencies between compile options or any other variables defined
in makefiles.
The dependencies especially indicate the relationship between a variable
parent (assigner) and a variable itself as a child (assignee).
The relationship between variable parent and variable child usually defined
by conditional lines (ifeq/ifneq/ifdef/ifndef).

By recording the operation history of these conditional lines, we can keep
the operation history of a variable child and its variable parents.
These operation histories are stored in value_record and parent_records.
A value_record is a linking list to record each value was assigned to a
variable caused by a conditional line. And the parent_record will keep the
variables which made the value is assigned to this child value.

Developers can simply dump all these informations by simply use command line
`make --dep` to dump the dependency chain stored in makefile for a software

Software projects is growing bigger and bigger nowadays. By adding this
--dep features may also help developers not only to understand the relationship
between definitions in makefiles and also test if their makefile has problem
(loop) in conditional checking for variables.

Here comes the examples:

  A = AA
  B = BB

  ifeq ($(A),AA)
  C = CC

  ifeq ($(A),AA)
  D = DD
  ifeq ($(B),BB)
  C += CCC

  ifeq ($(D),DD)
  ifeq ($(B),BB)
  E = EE

Output of `make --dep`
A = AA
B = BB
value: CC, parent: A, value: AA;
value: CCC, parent: A, value: AA; parent: B, value: BB;
D = DD
value: DD, parent: A, value: AA;
E = EE
value: EE, parent: D ,value DD; parent: B, value: BB;
parent name: D, value: DD, parent: A, value AA;

The following are some thought and futhur extension of current implementations.
1. Since the make variable evaluation were stateless and no records stored.
This implementation will use much more memory and linear search for linking list
to value_records and parent records.
I think we can add something conditional checking if the "--dep" option has been
enabled. There is no need to maintain these records if "--dep" option was not

2. Loop detection and blacklists support.
Actually, I've found some makefile will wrote like this.

  A = AA
  ifeq ($(A),)
  A =

This kind of codes will lead a loop for a variable link a parents to itself.
When dump all parents will cause a infinite loop.
Some project may really need this kind of code for build.
I think add a blacklist to avoid make to assign this kind of variable
as parent could help.

3. Support print depth when dump dependency informations?
If the dependency chain of a variable is very deep.
Should we support the "depth" parameters to limits the depth of
printing parents?

4. Print format.
Is there any format could help developer or post scripts to parse the dependency
output more easily?

5. Test cases.
I only write several makefile to test these patches.
If there are official test cases, please tell me where they are and I can try
them on current implementation.

I think futher discussion is needed since I didn't very understand how possible
can this implementation help others in practice.

Best regards,
Macpaul Lin

Best regards,
Macpaul Lin

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