gem install pg ne fonctionne pas sur OSX Lion

il y a des variantes de cette question rebondissant autour de ainsi, mais aucun d'eux semblent avoir une réponse qui résout mon problème.

Je cours OSX Lion (10.7.3). Le dernier XCode est installé.

J'ai installé Postgres en utilisant les Postgres.package de l'application de postgresapp.com.

mais quand j'essaie d'installer le gem pg, j'obtiens un échec:

$ gem install pg -- --with-pg-config=/Applications/Postgres.app/Contents/MacOS/bin/pg_config
Building native extensions.  This could take a while...
ERROR:  Error installing pg:
    ERROR: Failed to build gem native extension.

        /Users/disaacs/.rvm/rubies/ruby-1.9.3-p125/bin/ruby extconf.rb --with-pg-config=/Applications/Postgres.app/Contents/MacOS/bin/pg_config
Using config values from /Applications/Postgres.app/Contents/MacOS/bin/pg_config
checking for libpq-fe.h... *** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of
necessary libraries and/or headers.  Check the mkmf.log file for more
details.  You may need configuration options.

Provided configuration options:
    --with-opt-dir
    --with-opt-include
    --without-opt-include=${opt-dir}/include
    --with-opt-lib
    --without-opt-lib=${opt-dir}/lib
    --with-make-prog
    --without-make-prog
    --srcdir=.
    --curdir
    --ruby=/Users/disaacs/.rvm/rubies/ruby-1.9.3-p125/bin/ruby
    --with-pg
    --without-pg
    --with-pg-dir
    --without-pg-dir
    --with-pg-include
    --without-pg-include=${pg-dir}/include
    --with-pg-lib
    --without-pg-lib=${pg-dir}/lib
    --with-pg-config
/Users/disaacs/.rvm/rubies/ruby-1.9.3-p125/lib/ruby/1.9.1/mkmf.rb:381:in `try_do': The compiler failed to generate an executable file. (RuntimeError)
You have to install development tools first.
    from /Users/disaacs/.rvm/rubies/ruby-1.9.3-p125/lib/ruby/1.9.1/mkmf.rb:506:in `try_cpp'
    from /Users/disaacs/.rvm/rubies/ruby-1.9.3-p125/lib/ruby/1.9.1/mkmf.rb:970:in `block in find_header'
    from /Users/disaacs/.rvm/rubies/ruby-1.9.3-p125/lib/ruby/1.9.1/mkmf.rb:790:in `block in checking_for'
    from /Users/disaacs/.rvm/rubies/ruby-1.9.3-p125/lib/ruby/1.9.1/mkmf.rb:284:in `block (2 levels) in postpone'
    from /Users/disaacs/.rvm/rubies/ruby-1.9.3-p125/lib/ruby/1.9.1/mkmf.rb:254:in `open'
    from /Users/disaacs/.rvm/rubies/ruby-1.9.3-p125/lib/ruby/1.9.1/mkmf.rb:284:in `block in postpone'
    from /Users/disaacs/.rvm/rubies/ruby-1.9.3-p125/lib/ruby/1.9.1/mkmf.rb:254:in `open'
    from /Users/disaacs/.rvm/rubies/ruby-1.9.3-p125/lib/ruby/1.9.1/mkmf.rb:280:in `postpone'
    from /Users/disaacs/.rvm/rubies/ruby-1.9.3-p125/lib/ruby/1.9.1/mkmf.rb:789:in `checking_for'
    from /Users/disaacs/.rvm/rubies/ruby-1.9.3-p125/lib/ruby/1.9.1/mkmf.rb:969:in `find_header'
    from extconf.rb:40:in `<main>'


Gem files will remain installed in /Users/disaacs/.rvm/gems/ruby-1.9.3-p125/gems/pg-0.13.2 for inspection.
Results logged to /Users/disaacs/.rvm/gems/ruby-1.9.3-p125/gems/pg-0.13.2/ext/gem_make.out

la sortie de la commande /Applications/Postgres.app/Contents/MacOS/bin/pg_config est:

$ /Applications/Postgres.app/Contents/MacOS/bin/pg_config
BINDIR = /Applications/Postgres.app/Contents/MacOS/bin
DOCDIR = /Applications/Postgres.app/Contents/MacOS/share/doc
HTMLDIR = /Applications/Postgres.app/Contents/MacOS/share/doc
INCLUDEDIR = /Applications/Postgres.app/Contents/MacOS/include
PKGINCLUDEDIR = /Applications/Postgres.app/Contents/MacOS/include
INCLUDEDIR-SERVER = /Applications/Postgres.app/Contents/MacOS/include/server
LIBDIR = /Applications/Postgres.app/Contents/MacOS/lib
PKGLIBDIR = /Applications/Postgres.app/Contents/MacOS/lib
LOCALEDIR = /Applications/Postgres.app/Contents/MacOS/share/locale
MANDIR = /Applications/Postgres.app/Contents/MacOS/share/man
SHAREDIR = /Applications/Postgres.app/Contents/MacOS/share
SYSCONFDIR = /Applications/Postgres.app/Contents/MacOS/etc
PGXS = /Applications/Postgres.app/Contents/MacOS/lib/pgxs/src/makefiles/pgxs.mk
CONFIGURE = '--prefix=/Users/mattt/Code/heroku/Postgres/Postgres/Vendor/postgres' '--enable-thread-safety' '--with-openssl' '--with-gssapi' '--with-bonjour' '--with-krb5' '--with-libxml' '--with-libxslt' '--with-ossp-uuid' '--with-perl' '--with-python'
CC = gcc
CPPFLAGS = -I/usr/include/libxml2
CFLAGS = -O2 -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Wendif-labels -Wformat-security -fno-strict-aliasing -fwrapv
CFLAGS_SL = 
LDFLAGS = -Wl,-dead_strip_dylibs
LDFLAGS_EX = 
LDFLAGS_SL = 
LIBS = -lpgport -lxslt -lxml2 -lssl -lcrypto -lgssapi_krb5 -lz -lreadline -lm 
VERSION = PostgreSQL 9.1.3

tous ces paramètres semblent corrects, sauf pour la variable CONFIGURE (qui semble renvoyer à un autre ordinateur --je n'ai pas d'utilisateur nommé mattt).

le contenu du mkmf.fichier journal sont

"/usr/bin/gcc-4.2 -o conftest -I/Users/disaacs/.rvm/rubies/ruby-1.9.3-p125/include/ruby-1.9.1/x86_64-darwin10.8.0 -I/Users/disaacs/.rvm/rubies/ruby-1.9.3-p125/include/ruby-1.9.1/ruby/backward -I/Users/disaacs/.rvm/rubies/ruby-1.9.3-p125/include/ruby-1.9.1 -I. -I/Users/disaacs/.rvm/usr/include -D_XOPEN_SOURCE -D_DARWIN_C_SOURCE   -I/Applications/Postgres.app/Contents/MacOS/include  -O3 -ggdb -Wextra -Wno-unused-parameter -Wno-parentheses -Wno-long-long -Wno-missing-field-initializers -Wpointer-arith -Wwrite-strings -Wdeclaration-after-statement -Wshorten-64-to-32 -Wimplicit-function-declaration  -fno-common -pipe conftest.c  -L. -L/Users/disaacs/.rvm/rubies/ruby-1.9.3-p125/lib -L/Users/disaacs/.rvm/usr/lib -L. -L/usr/local/lib -L/Applications/Postgres.app/Contents/MacOS/lib     -lruby.1.9.1  -lpthread -ldl -lobjc "
checked program was:
/* begin */
1: #include "ruby.h"
2:
3: int main() {return 0;}
/* end */

toute suggestion serait appréciée.

j'ai regardé l'extconf.fichier rb, et après quelques déboguages j'ai trouvé que c'est un appel à

find_header ('libpq-fe.h')

c'est un échec. Non pas parce que libpq-fe.h n'est pas là, mais parce que la méthode find_header elle-même est défaillante. J'ai essayé d'exécuter find_header en utilisant irb, et j'ai eu la même erreur:

$ irb
1.9.3-p125 :001 > require 'mkmf'
 => true 
1.9.3-p125 :002 > find_header 'libpq-fe.h'
checking for libpq-fe.h... RuntimeError: The compiler failed to generate an executable file.
You have to install development tools first.

EDIT:

a découvert que mon ordinateur devait être encore plus bourré que je le pensais. Je faisais l'installation de bundle pour un autre projet, et j'ai eu un échec très similaire en installant le Gem sqlite3.

checking for sqlite3.h... *** extconf.rb failed ***

je n'ai jamais eu de problèmes avec le gem sqlite3 dans le passé.