Correct code fails to build due to hardcoded -Werror

[milancurcic]

fpm is currently making gfortran fail on warning by hardcoding -Werror. Removing -Werror from fpm.toml doesn't change this behavior (I understand specifying flags via fpm.toml may not be implemented yet.

However, in the meantime, we shouldn't use -Werror because it's making correct code to fail. For example:

[milan@gary test_project_error]$ cat src/mylib.f90 
real :: a, b
a = 2.
b = 2.
print *, a == b
end
[milan@gary test_project_error]$ cat fpm.toml 
name = "package-name"
version = "0.1.0"
license = "BSD3"
author = "Author name here"
maintainer = "example@example.com"
copyright = "2020 Author name here"
dependencies = []
compiler = "gfortran"
devel-options = ["-g", "-Wall", "-Wextra", "-pedantic"]
release-options = ["-O3"]

[library]
source-dirs = "src"
[milan@gary test_project_error]$ fpm build
# gfortran (for build/debug/library/mylib.o build/debug/library/mylib.mod)
src/mylib.f90:4:8:

 print *, a == b
        1
Error: Equality comparison for REAL(4) at (1) [-Werror=compare-reals]
f951: all warnings being treated as errors
fpm-exe: Error when running Shake build system:
  at want, called at src/Build.hs:188:11 in fpm-0.1.0.0-9zFE4ut013U9YSOSmXT3I3:Build
* Depends on: build/debug/library/package-name.a
  at need, called at src/Build.hs:186:13 in fpm-0.1.0.0-9zFE4ut013U9YSOSmXT3I3:Build
* Depends on: build/debug/library/mylib.o
  at &%>, called at src/Build.hs:166:11 in fpm-0.1.0.0-9zFE4ut013U9YSOSmXT3I3:Build
* Depends on: build/debug/library/mylib.o build/debug/library/mylib.mod
  at cmd, called at src/Build.hs:179:19 in fpm-0.1.0.0-9zFE4ut013U9YSOSmXT3I3:Build
* Raised the exception:
Development.Shake.cmd, system command failed
Command line: gfortran -c -Jbuild/debug/library -Wall -Wextra -Wimplicit-interface -Werror -fPIC -fmax-errors=1 -g -fbounds-check -fcheck-array-temporaries -fbacktrace -o build/debug/library/mylib.o src/mylib.f90
Exit code: 1
Stderr:
src/mylib.f90:4:8:

 print *, a == b
        1
Error: Equality comparison for REAL(4) at (1) [-Werror=compare-reals]
f951: all warnings being treated as errors

What do you think?

[LKedward]

I think Werror is not your friend and should not be used here; especially here where we cannot guarantee a specific compiler version.
Latest gfortran actually produces spurious warnings for certain derived-type allocations so Werror would completely prevent you from producing a debug build.
#50

[everythingfunctional]

As I mentioned on the PR, I'm fine with removing the -Werror flag from the default list. But in this instance I will point out that comparison of reals really is a bad idea. Floating point math means that equality will almost surely never be true. For example, I'm pretty sure (1.0 / 3.0) == ((1.0 / 9.0) * 3.0) is false, when you really would expect it to be true.

[milancurcic]

In most cases, yes, and that's why there should be a warning for it. :)