Configure script is inconsistent regarding escaping in user-supplied values

[davmac314]

Arguments to "configure" which go into variables in mconfig (such as CXX) are used inconsistently in the configure script. In most cases this doesn't matter, but it is sloppy and really should be fixed.

Eg. if CXX contains a compiler, then try_cxx_argument function does:

if $CXX $CXXFLAGS [etc]

Which will run a, with compiler as an argument followed by whatever is in CXXFLAGS (with value subject to word splitting by the shell).
If CXX contains "a compiler", it will run "a (with compiler" as argument), rather than having the shell interpret the quotes.
However, in this latter case, the mconfig value is written as:

CXX=$CXX

... which is a Makefile variable, which will be expanded via $(CXX) in the Makefile (not via the shell), and will then be subject to shell quoting, so that it will run a compiler.

I.e. the Makefile build will use a different compiler than what was tested in the configure script.

Currently the configure --help output says:

Note: paths specified via --prefix/--exec-prefix/--sbindir/--mandir, and build variable values,
must be escaped for use in a makefile and in shell commands. If there are spaces in paths it is
recommended to prepend a backslash (\) to them.
For example: ./configure --prefix="/home/my\ home"

This is already problematic, how do you escape a value for use in a makefile and in shell commands? The script should accept one or the other and modify the value as necessary in different contexts.
But also, as pointed out above, the example doesn't work for variables that are actually used in the configure script (such as CXX, CXXFLAGS, etc) because the script doesn't use them in a way that causes the shell to re-interpret the values after expansion (as it would if done eg via eval).

[davmac314]

how do you escape a value for use in a makefile and in shell commands?

Thinking further, the values supplied by the user (commands, command arguments) should be escaped for the shell (only).

However, paths, such as for --prefix, should ideally not require pre-escaping by the user (in the manner suggested by the configure --help output currently). That may require escaping them (automatically in the script) for use in eval context and/or when written to the makefile fragment (mconfig).

[mobin-2008]

About the single value variables such as $CXX the fix I think would be quoting value when using it and putting it in mconfig:

SBINDIR="$SBINDIR"
...
CXX="$CXX"

and then tell the user to escape value only for configure script (shell).

I tested my idea with $CXX case: I created a script called my which prints 1 and executes into compiler and also created another script called my compiler which prints 2 and then executes into compiler. I changed all usage of $CXX to "$CXX" in configure and passed "my compiler" to configure as such:

./configure CXX="$PWD/my compiler"
or
./configure CXX=$PWD/my\ compiler

The result was correct, The my compiler was used not my with compiler argument in both configure and Makefiles.

"/[Redacted]/my compiler"  -std=c++11 -Wall -Os -fno-plt -fno-rtti -flto  -MMD -MP -Iincludes -I../dasynq/include -I../build/includes -c dinit-log.cc -o dinit-log.o
2

But about multi value variables such as $CXXFLAGS we can't just quote value because it contains more than just one argument. I'm thinking about how to fix this.

[davmac314]

The result was correct, The my compiler was used not my with compiler argument in both configure and Makefiles.

That's not correct. It should be the opposite in both.

Usually a configure program allows for example ./configure CXX="g++ -std=c++11" and then the compiler is g++ with the argument -std=c++11 always given.

If you wanted to use my compiler as the compiler you should quote it. Eg ./configure CXX='"./my compiler"'.

Putting quotes on the command line you use to run configure is not the same as supplying a value that contains quotes. What you did with:

./configure CXX="$PWD/my compiler"

Was to run ./configure with a single argument value:

CXX=/some/directory/my compiler

The argument value isn't quoted for anything.

[davmac314]

Also:

About the single value variables such as $CXX the fix I think would be quoting value when using it and putting it in mconfig

You can never turn a value from unquoted to quoted just by putting quotes around it. What if the value itself had a quote character in it?

[davmac314]

But about multi value variables such as $CXXFLAGS we can't just quote value because it contains more than just one argument. I'm thinking about how to fix this.

You need to use eval to handle things properly. That allows user-supplied value to have quotes which are then re-interpreted by the shell, exactly as is needed.