add_custom_command: Add DEPENDS_EXPLICIT_ONLY option for Ninja

Add option `DEPENDS_EXPLICIT_ONLY` to `add_custom_command` to indicate
that implicit dependencies coming from users of the output are not
needed, and only consider dependencies explicitly specified in the
custom command.

Fixes: #17097

4 files changed, 50 insertions, 26 deletions

diff --git a/Source/cmAddCustomCommandCommand.cxx b/Source/cmAddCustomCommandCommand.cxx
index 831e9c7..65a8eb5 100644
--- a/Source/cmAddCustomCommandCommand.cxx
+++ b/Source/cmAddCustomCommandCommand.cxx
@@ -49,6 +49,7 @@ bool cmAddCustomCommandCommand(std::vector<std::string> const& args,
   bool append = false;
   bool uses_terminal = false;
   bool command_expand_lists = false;
+  bool depends_explicit_only = false;
   std::string implicit_depends_lang;
   cmImplicitDependsList implicit_depends;
 
@@ -104,6 +105,7 @@ bool cmAddCustomCommandCommand(std::vector<std::string> const& args,
   MAKE_STATIC_KEYWORD(USES_TERMINAL);
   MAKE_STATIC_KEYWORD(VERBATIM);
   MAKE_STATIC_KEYWORD(WORKING_DIRECTORY);
+  MAKE_STATIC_KEYWORD(DEPENDS_EXPLICIT_ONLY);
 #undef MAKE_STATIC_KEYWORD
   static std::unordered_set<std::string> const keywords{
     keyAPPEND,
@@ -126,7 +128,8 @@ bool cmAddCustomCommandCommand(std::vector<std::string> const& args,
     keyTARGET,
     keyUSES_TERMINAL,
     keyVERBATIM,
-    keyWORKING_DIRECTORY
+    keyWORKING_DIRECTORY,
+    keyDEPENDS_EXPLICIT_ONLY
   };
 
   for (std::string const& copy : args) {
@@ -155,6 +158,8 @@ bool cmAddCustomCommandCommand(std::vector<std::string> const& args,
         uses_terminal = true;
       } else if (copy == keyCOMMAND_EXPAND_LISTS) {
         command_expand_lists = true;
+      } else if (copy == keyDEPENDS_EXPLICIT_ONLY) {
+        depends_explicit_only = true;
       } else if (copy == keyTARGET) {
         doing = doing_target;
       } else if (copy == keyARGS) {
@@ -329,6 +334,7 @@ bool cmAddCustomCommandCommand(std::vector<std::string> const& args,
   cc->SetDepfile(depfile);
   cc->SetJobPool(job_pool);
   cc->SetCommandExpandLists(command_expand_lists);
+  cc->SetDependsExplicitOnly(depends_explicit_only);
   if (source.empty() && output.empty()) {
     // Source is empty, use the target.
     mf.AddCustomCommandToTarget(target, cctype, std::move(cc));
diff --git a/Source/cmCustomCommand.cxx b/Source/cmCustomCommand.cxx
index 5b63996..e12cf70 100644
--- a/Source/cmCustomCommand.cxx
+++ b/Source/cmCustomCommand.cxx
@@ -164,6 +164,16 @@ void cmCustomCommand::SetCommandExpandLists(bool b)
   this->CommandExpandLists = b;
 }
 
+bool cmCustomCommand::GetDependsExplicitOnly() const
+{
+  return this->DependsExplicitOnly;
+}
+
+void cmCustomCommand::SetDependsExplicitOnly(bool b)
+{
+  this->DependsExplicitOnly = b;
+}
+
 const std::string& cmCustomCommand::GetDepfile() const
 {
   return this->Depfile;
diff --git a/Source/cmCustomCommand.h b/Source/cmCustomCommand.h
index 3671ad9..1e68dbf 100644
--- a/Source/cmCustomCommand.h
+++ b/Source/cmCustomCommand.h
@@ -102,6 +102,11 @@ public:
   bool GetCommandExpandLists() const;
   void SetCommandExpandLists(bool b);
 
+  /** Set/Get whether to use additional dependencies coming from
+      users of OUTPUT of the custom command. */
+  bool GetDependsExplicitOnly() const;
+  void SetDependsExplicitOnly(bool b);
+
   /** Set/Get the depfile (used by the Ninja generator) */
   const std::string& GetDepfile() const;
   void SetDepfile(const std::string& depfile);
@@ -141,6 +146,7 @@ private:
   bool CommandExpandLists = false;
   bool StdPipesUTF8 = false;
   bool HasMainDependency_ = false;
+  bool DependsExplicitOnly = false;
 
 // Policies are NEW for synthesized custom commands, and set by cmMakefile for
 // user-created custom commands.
diff --git a/Source/cmLocalNinjaGenerator.cxx b/Source/cmLocalNinjaGenerator.cxx
index 1e2ea2a..f8027c0 100644
--- a/Source/cmLocalNinjaGenerator.cxx
+++ b/Source/cmLocalNinjaGenerator.cxx
@@ -586,32 +586,34 @@ void cmLocalNinjaGenerator::WriteCustomCommandBuildStatement(
 
     cmNinjaDeps orderOnlyDeps;
 
-    // A custom command may appear on multiple targets.  However, some build
-    // systems exist where the target dependencies on some of the targets are
-    // overspecified, leading to a dependency cycle.  If we assume all target
-    // dependencies are a superset of the true target dependencies for this
-    // custom command, we can take the set intersection of all target
-    // dependencies to obtain a correct dependency list.
-    //
-    // FIXME: This won't work in certain obscure scenarios involving indirect
-    // dependencies.
-    auto j = targets.begin();
-    assert(j != targets.end());
-    this->GetGlobalNinjaGenerator()->AppendTargetDependsClosure(
-      *j, orderOnlyDeps, ccg.GetOutputConfig(), fileConfig, ccgs.size() > 1);
-    std::sort(orderOnlyDeps.begin(), orderOnlyDeps.end());
-    ++j;
-
-    for (; j != targets.end(); ++j) {
-      std::vector<std::string> jDeps;
-      std::vector<std::string> depsIntersection;
+    if (!cc->GetDependsExplicitOnly()) {
+      // A custom command may appear on multiple targets.  However, some build
+      // systems exist where the target dependencies on some of the targets are
+      // overspecified, leading to a dependency cycle.  If we assume all target
+      // dependencies are a superset of the true target dependencies for this
+      // custom command, we can take the set intersection of all target
+      // dependencies to obtain a correct dependency list.
+      //
+      // FIXME: This won't work in certain obscure scenarios involving indirect
+      // dependencies.
+      auto j = targets.begin();
+      assert(j != targets.end());
       this->GetGlobalNinjaGenerator()->AppendTargetDependsClosure(
-        *j, jDeps, ccg.GetOutputConfig(), fileConfig, ccgs.size() > 1);
-      std::sort(jDeps.begin(), jDeps.end());
-      std::set_intersection(orderOnlyDeps.begin(), orderOnlyDeps.end(),
-                            jDeps.begin(), jDeps.end(),
-                            std::back_inserter(depsIntersection));
-      orderOnlyDeps = depsIntersection;
+        *j, orderOnlyDeps, ccg.GetOutputConfig(), fileConfig, ccgs.size() > 1);
+      std::sort(orderOnlyDeps.begin(), orderOnlyDeps.end());
+      ++j;
+
+      for (; j != targets.end(); ++j) {
+        std::vector<std::string> jDeps;
+        std::vector<std::string> depsIntersection;
+        this->GetGlobalNinjaGenerator()->AppendTargetDependsClosure(
+          *j, jDeps, ccg.GetOutputConfig(), fileConfig, ccgs.size() > 1);
+        std::sort(jDeps.begin(), jDeps.end());
+        std::set_intersection(orderOnlyDeps.begin(), orderOnlyDeps.end(),
+                              jDeps.begin(), jDeps.end(),
+                              std::back_inserter(depsIntersection));
+        orderOnlyDeps = depsIntersection;
+      }
     }
 
     const std::vector<std::string>& outputs = ccg.GetOutputs();