add the only target

This makes the following work correctly:
  make only TGTS="foo bar" -j2
note that
  make foo bar -j2
is not doing what you think

4 files changed, 34 insertions, 0 deletions

diff --git a/doc/refman/RefMan-uti.tex b/doc/refman/RefMan-uti.tex
index 104d7cd9e..08cdbee50 100644
--- a/doc/refman/RefMan-uti.tex
+++ b/doc/refman/RefMan-uti.tex
@@ -132,6 +132,14 @@ as in {\tt make -f Makefile target} from another Makefile.
 	{\tt CoqMakefile.local}
 \end{itemize}
 
+\paragraph{Note: building a subset of the targets with -j}
+
+To build, say, two targets \texttt{foo.vo} and \texttt{bar.vo}
+in parallel one can use \texttt{make only TGTS="foo.vo bar.vo" -j}.
+
+Note that \texttt{make foo.vo bar.vo -j} has a different meaning for
+the make utility, in particular it may build a shared prerequisite twice.
+
 \section[Modules dependencies]{Modules dependencies\label{Dependencies}\index{Dependencies}
   \ttindex{coqdep}}
 
diff --git a/test-suite/coq-makefile/only/_CoqProject b/test-suite/coq-makefile/only/_CoqProject
new file mode 100644
index 000000000..357384fdd
--- /dev/null
+++ b/test-suite/coq-makefile/only/_CoqProject
@@ -0,0 +1,11 @@
+-R theories/ test
+-R src/ test
+-I src/
+
+./src/test_plugin.mlpack
+./src/test.ml4
+./src/test.mli
+./src/test_aux.ml
+./src/test_aux.mli
+./theories/test.v
+./theories/sub/testsub.v
diff --git a/test-suite/coq-makefile/only/run.sh b/test-suite/coq-makefile/only/run.sh
new file mode 100755
index 000000000..4b471bcb8
--- /dev/null
+++ b/test-suite/coq-makefile/only/run.sh
@@ -0,0 +1,12 @@
+#!/bin/sh
+
+#set -x
+set -e
+
+. ../template/init.sh
+
+coq_makefile -f _CoqProject -o Makefile
+make only TGTS="src/test.cmi src/test_aux.cmi" -j2
+test -f src/test.cmi
+test -f src/test_aux.cmi
+! test -f src/test.cmo
diff --git a/tools/CoqMakefile.in b/tools/CoqMakefile.in
index 1de7a5c24..fdcd2ed79 100644
--- a/tools/CoqMakefile.in
+++ b/tools/CoqMakefile.in
@@ -278,6 +278,9 @@ validate: $(VOFILES)
 	$(COQCHK) $(COQCHKFLAGS) $(notdir $(^:.vo=))
 .PHONY: validate
 
+only: $(TGTS)
+.PHONY: only
+
 # Documentation targets #######################################################
 
 html: $(GLOBFILES) $(VFILES)