cmake: Teach --build to reject multiple --target options

Previously we did not clearly document that `--target` is only supported
to be specified once.  Even worse, specifying it multiple times would
silently ignore any previously specified targets and only build the last
target.

Update the documentation to specify this.  Update the implementation to
reject multiple `--target` options to prevent user errors.

7 files changed, 28 insertions, 1 deletions

diff --git a/Help/manual/cmake.1.rst b/Help/manual/cmake.1.rst
index 273a780..959148e 100644
--- a/Help/manual/cmake.1.rst
+++ b/Help/manual/cmake.1.rst
@@ -58,6 +58,7 @@ Options
 
    <dir>          = Project binary directory to be built.
    --target <tgt> = Build <tgt> instead of default targets.
+                    May only be specified once.
    --config <cfg> = For multi-configuration tools, choose <cfg>.
    --clean-first  = Build target 'clean' first, then build.
                     (To clean only, use --target 'clean'.)
diff --git a/Help/release/dev/error-multiple-targets.rst b/Help/release/dev/error-multiple-targets.rst
new file mode 100644
index 0000000..060b26b
--- /dev/null
+++ b/Help/release/dev/error-multiple-targets.rst
@@ -0,0 +1,6 @@
+error-multiple-targets
+----------------------
+
+* The :manual:`cmake(1)` ``--build`` command-line tool now rejects multiple
+  ``--target`` options with an error instead of silently ignoring all but the
+  last one.
diff --git a/Source/cmakemain.cxx b/Source/cmakemain.cxx
index a06b26f..c60b962 100644
--- a/Source/cmakemain.cxx
+++ b/Source/cmakemain.cxx
@@ -60,6 +60,7 @@ static const char * cmDocumentationUsageNote[][2] =
 #define CMAKE_BUILD_OPTIONS                                             \
   "  <dir>          = Project binary directory to be built.\n"          \
   "  --target <tgt> = Build <tgt> instead of default targets.\n"        \
+  "                   May only be specified once.\n"                    \
   "  --config <cfg> = For multi-configuration tools, choose <cfg>.\n"   \
   "  --clean-first  = Build target 'clean' first, then build.\n"        \
   "                   (To clean only, use --target 'clean'.)\n"         \
@@ -386,6 +387,7 @@ static int do_build(int ac, char const* const* av)
   std::string dir;
   std::vector<std::string> nativeOptions;
   bool clean = false;
+  bool hasTarget = false;
 
   enum Doing { DoingNone, DoingDir, DoingTarget, DoingConfig, DoingNative};
   Doing doing = DoingDir;
@@ -397,7 +399,17 @@ static int do_build(int ac, char const* const* av)
       }
     else if(strcmp(av[i], "--target") == 0)
       {
-      doing = DoingTarget;
+      if (!hasTarget)
+        {
+        doing = DoingTarget;
+        hasTarget = true;
+        }
+      else
+        {
+        std::cerr << "'--target' may not be specified more than once.\n\n";
+        dir = "";
+        break;
+        }
       }
     else if(strcmp(av[i], "--config") == 0)
       {
diff --git a/Tests/RunCMake/CommandLine/BuildDir--build-multiple-targets-result.txt b/Tests/RunCMake/CommandLine/BuildDir--build-multiple-targets-result.txt
new file mode 100644
index 0000000..d00491f
--- /dev/null
+++ b/Tests/RunCMake/CommandLine/BuildDir--build-multiple-targets-result.txt
@@ -0,0 +1 @@
+1
diff --git a/Tests/RunCMake/CommandLine/BuildDir--build-multiple-targets-stderr.txt b/Tests/RunCMake/CommandLine/BuildDir--build-multiple-targets-stderr.txt
new file mode 100644
index 0000000..f2cbaa6
--- /dev/null
+++ b/Tests/RunCMake/CommandLine/BuildDir--build-multiple-targets-stderr.txt
@@ -0,0 +1,3 @@
+^'--target' may not be specified more than once\.
++
+Usage: cmake --build <dir> \[options\] \[-- \[native-options\]\]
diff --git a/Tests/RunCMake/CommandLine/BuildDir/CMakeLists.txt b/Tests/RunCMake/CommandLine/BuildDir/CMakeLists.txt
index 20df108..d2a2831 100644
--- a/Tests/RunCMake/CommandLine/BuildDir/CMakeLists.txt
+++ b/Tests/RunCMake/CommandLine/BuildDir/CMakeLists.txt
@@ -3,3 +3,5 @@ add_custom_command(
   COMMAND ${CMAKE_COMMAND} -E echo CustomCommand > output.txt
   )
 add_custom_target(CustomTarget ALL DEPENDS output.txt)
+add_custom_target(CustomTarget2 ALL DEPENDS output.txt)
+add_custom_target(CustomTarget3 ALL DEPENDS output.txt)
diff --git a/Tests/RunCMake/CommandLine/RunCMakeTest.cmake b/Tests/RunCMake/CommandLine/RunCMakeTest.cmake
index e3b73ff..a07bbbe 100644
--- a/Tests/RunCMake/CommandLine/RunCMakeTest.cmake
+++ b/Tests/RunCMake/CommandLine/RunCMakeTest.cmake
@@ -51,6 +51,8 @@ function(run_BuildDir)
   run_cmake(BuildDir)
   run_cmake_command(BuildDir--build ${CMAKE_COMMAND} -E chdir ..
     ${CMAKE_COMMAND} --build BuildDir-build --target CustomTarget)
+  run_cmake_command(BuildDir--build-multiple-targets ${CMAKE_COMMAND} -E chdir ..
+    ${CMAKE_COMMAND} --build BuildDir-build --target CustomTarget2 --target CustomTarget3)
 endfunction()
 run_BuildDir()