Save even environment variables in the configuration file.

2 files changed, 41 insertions, 25 deletions

diff --git a/comfignat.mk b/comfignat.mk
index 7916743..23e71aa 100644
--- a/comfignat.mk
+++ b/comfignat.mk
@@ -496,33 +496,46 @@ ${builddir}/Makefile: | ${builddir}
 # How to save configured variables:
 configure:: ${builddir}/Makefile
 	@echo "Writing ${configuration}."
-	@( ${foreach variable,${configuration_variables}, \
-	             ${if ${or ${findstring command line, \
-	                                    ${origin ${variable}}}, \
-	                       ${filter true,${${variable}_is_overridden}}, \
-	                       ${filter true,${${variable}_is_configured}}}, \
-	                  echo 'ifneq "$${origin ${variable}}" "command line"';\
-	                  echo '  override ${variable} = ${value ${variable}}';\
+	@( ${foreach var,${configuration_variables}, \
+	             ${if ${or ${findstring command line,${origin ${var}}}, \
+	                       ${filter true,${${var}_is_overridden}}, \
+	                       ${filter true,${${var}_is_configured}}}, \
+	                  echo 'ifneq "$${origin ${var}}" "command line"'; \
+	                  echo '   override ${var} = ${value ${var}}';\
 	                  echo 'endif'; \
-	                  echo '${variable}_is_configured = true'; \
-	                  echo;}} \
+	                  echo '${var}_is_configured = true'; \
+	                  echo;, \
+	             ${if ${or ${findstring environment,${origin ${var}}}, \
+	                       ${filter true,${${var}_is_weakly_configured}}}, \
+	                  echo 'ifneq "$${origin ${var}}" "environment"'; \
+	                  echo '   ${var} = ${value ${var}}'; \
+	                  echo 'endif'; \
+	                  echo '${var}_is_weakly_configured = true'; \
+	                  echo;}}} \
 	   true \
 	 ) > "${configuration}"
 # Out of the variables listed in configuration_variables, all that were
-# overridden on the command line, and all that were previously configured, are
-# written to the configuration file. Configured values override defaults
-# defined later in the containing makefile, but can be overridden on the
-# command line. A variable is considered previously configured if there is
-# another variable with "_is_configured" appended to its name and a value of
-# "true". Such a variable is also written for each configured variable. As a
-# side effect of this it is possible to delete a variable V from the
-# configuration by running "make configure V_is_configured=false".
+# overridden on the command line, all that are set in the environment and not
+# overridden elsewhere, and all that were previously configured, are written
+# to the configuration file. Command-line-configured values override defaults
+# assigned later in the containing makefile, but can be overridden on the
+# command line. Environment-configured values override defaults assigned with
+# "?=", but can be overridden in the environment or on the command line. A
+# variable is considered previously configured if there is another variable
+# with "_is_configured" or "_is_weakly_configured" appended to its name and a
+# value of "true". Such a variable is also written for each configured
+# variable. As a side effect of this it is possible to delete a variable V from
+# the configuration by running "make configure V_is_configured=false
+# V_is_weakly_configured=false".
 
 # How to show the values of configured variables:
 show_configuration::
-	@${foreach variable,${configuration_variables}, \
-	           ${if ${filter true,${${variable}_is_configured}}, \
-	                echo '${variable} = ${value ${variable}}';}}
+	@${foreach var,${configuration_variables}, \
+	           ${if ${filter true,${${var}_is_configured}}, \
+	                echo '${var} = ${value ${var}}';} \
+	           ${if ${filter true,${${var}_is_weakly_configured}}, \
+	                echo '${var} ?= ${value ${var}}';}} \
+	 true
 
 # How to preprocess the project Comfignat:
 ${builddir}/comfignat.gpr: comfignat.gpr.gp | ${builddir}
diff --git a/manual.en.html b/manual.en.html
index 70703e4..a9d125a 100755
--- a/manual.en.html
+++ b/manual.en.html
@@ -425,11 +425,14 @@ your default.</p>
 
 <p>Those Make variables that installing users are expected to change can be
 configured persistently. Run "<samp>make configure</samp>" with some variables
-set on the command line. Those variables will then be saved in a file named
-<var>comfignat_configuration.mk</var>, which will be loaded in all subsequent
-Make invocations. Additional variables can be configured incrementally. The
-configuration can be erased with "<samp>make unconfigure</samp>" or as a part
-of "<samp>make distclean</samp>".</p>
+set on the command line or in the environment. Those variables will then be
+saved in a file named <var>comfignat_configuration.mk</var>, which will be
+loaded in all subsequent Make invocations. Additional variables can be
+configured incrementally. In subsequent Make invocations environment variables
+override values that were configured from the environment, and variables set on
+the command line override all configured values. The configuration can be
+erased with "<samp>make unconfigure</samp>" or as a part of
+"<samp>make distclean</samp>".</p>
 
 <p>The variables that can be configured are listed in the variable
 <var>configuration_variables</var>. The variables listed in <var>options</var>