Ninja: Handle depfiles with absolute paths to generated files

Ninja treats every (normalized) path as its own node.  It does not
recognize `/abs/path/to/file` in a depfile as matching `path/to/file`
even when `build.ninja` and the working directory are in `/abs/`.
See Ninja Issue 1251.  In cases where we pass absolute paths to the
compiler, it will write a depfile containing absolute paths.  If those
files are generated in the build tree by custom commands, `build.ninja`
references them by relative path in build statement outputs, so Ninja
does not hook up the dependency and rebuild the project correctly.

Add infrastructure to work around this problem by adding implicit
outputs to custom command build statements that reference the main
outputs by absolute path.  Use a `${cmake_ninja_workdir}` placeholder
to avoid repeating the base path.  For example:

    build out.txt | ${cmake_ninja_workdir}out.txt: CUSTOM_COMMAND ...

Ninja will create two nodes for the output file, one with a relative
path and one with an absolute path.  A depfile may then mention either
form of the path and Ninja will hook up the dependency.  Unfortunately
Ninja will also stat the file twice.

Issue: #13894
Fixes: #21865

5 files changed, 32 insertions, 1 deletions

diff --git a/Source/cmGlobalNinjaGenerator.cxx b/Source/cmGlobalNinjaGenerator.cxx
index a0baf3f..6034434 100644
--- a/Source/cmGlobalNinjaGenerator.cxx
+++ b/Source/cmGlobalNinjaGenerator.cxx
@@ -222,7 +222,7 @@ void cmGlobalNinjaGenerator::WriteBuild(std::ostream& os,
       }
     }
     // Write implicit outputs
-    if (!build.ImplicitOuts.empty()) {
+    if (!build.ImplicitOuts.empty() || !build.WorkDirOuts.empty()) {
       buildStr = cmStrCat(buildStr, " |");
       for (std::string const& implicitOut : build.ImplicitOuts) {
         buildStr = cmStrCat(buildStr, ' ', this->EncodePath(implicitOut));
@@ -230,6 +230,14 @@ void cmGlobalNinjaGenerator::WriteBuild(std::ostream& os,
           this->CombinedBuildOutputs.insert(implicitOut);
         }
       }
+      for (std::string const& workdirOut : build.WorkDirOuts) {
+        // Repeat some outputs, but expressed as absolute paths.
+        // This helps Ninja handle absolute paths found in a depfile.
+        // FIXME: Unfortunately this causes Ninja to stat the file twice.
+        // We could avoid this if Ninja Issue 1251 were fixed.
+        buildStr = cmStrCat(buildStr, " ${cmake_ninja_workdir}",
+                            this->EncodePath(workdirOut));
+      }
     }
 
     // Write the rule.
@@ -314,6 +322,12 @@ void cmGlobalNinjaGenerator::CCOutputs::Add(
 {
   for (std::string const& path : paths) {
     std::string out = this->GG->ConvertToNinjaPath(path);
+    if (this->GG->SupportsImplicitOuts() &&
+        !cmSystemTools::FileIsFullPath(out)) {
+      // This output is expressed as a relative path.  Repeat it,
+      // but expressed as an absolute path for Ninja Issue 1251.
+      this->WorkDirOuts.emplace_back(out);
+    }
     this->GG->SeenCustomCommandOutput(out);
     this->ExplicitOuts.emplace_back(std::move(out));
   }
@@ -340,6 +354,7 @@ void cmGlobalNinjaGenerator::WriteCustomCommandBuild(
     cmNinjaBuild build("CUSTOM_COMMAND");
     build.Comment = comment;
     build.Outputs = std::move(outputs.ExplicitOuts);
+    build.WorkDirOuts = std::move(outputs.WorkDirOuts);
     build.ExplicitDeps = std::move(explicitDeps);
     build.OrderOnlyDeps = std::move(orderOnlyDeps);
 
diff --git a/Source/cmGlobalNinjaGenerator.h b/Source/cmGlobalNinjaGenerator.h
index 2833367..7a3674e 100644
--- a/Source/cmGlobalNinjaGenerator.h
+++ b/Source/cmGlobalNinjaGenerator.h
@@ -121,6 +121,7 @@ public:
     }
     void Add(std::vector<std::string> const& outputs);
     cmNinjaDeps ExplicitOuts;
+    cmNinjaDeps WorkDirOuts;
   };
 
   void WriteCustomCommandBuild(std::string const& command,
diff --git a/Source/cmLocalNinjaGenerator.cxx b/Source/cmLocalNinjaGenerator.cxx
index 9eb3e46..fb6c730 100644
--- a/Source/cmLocalNinjaGenerator.cxx
+++ b/Source/cmLocalNinjaGenerator.cxx
@@ -263,6 +263,7 @@ void cmLocalNinjaGenerator::WriteBuildFileTop()
                                           this->GetConfigNames().front());
   }
   this->WriteNinjaFilesInclusionCommon(this->GetCommonFileStream());
+  this->WriteNinjaWorkDir(this->GetCommonFileStream());
 
   // For the rule file.
   this->WriteProjectHeader(this->GetRulesFileStream());
@@ -364,6 +365,17 @@ void cmLocalNinjaGenerator::WriteNinjaFilesInclusionCommon(std::ostream& os)
   os << "\n";
 }
 
+void cmLocalNinjaGenerator::WriteNinjaWorkDir(std::ostream& os)
+{
+  cmGlobalNinjaGenerator::WriteDivider(os);
+  cmGlobalNinjaGenerator::WriteComment(
+    os, "Logical path to working directory; prefix for absolute paths.");
+  cmGlobalNinjaGenerator* ng = this->GetGlobalNinjaGenerator();
+  std::string ninja_workdir = this->GetBinaryDirectory();
+  ng->StripNinjaOutputPathPrefixAsSuffix(ninja_workdir); // Also appends '/'.
+  os << "cmake_ninja_workdir = " << ng->EncodePath(ninja_workdir) << "\n";
+}
+
 void cmLocalNinjaGenerator::WriteProcessedMakefile(std::ostream& os)
 {
   cmGlobalNinjaGenerator::WriteDivider(os);
@@ -654,6 +666,7 @@ void cmLocalNinjaGenerator::WriteCustomCommandBuildStatement(
       cmNinjaBuild build("phony");
       build.Comment = cmStrCat("Phony custom command for ", mainOutput);
       build.Outputs = std::move(ccOutputs.ExplicitOuts);
+      build.WorkDirOuts = std::move(ccOutputs.WorkDirOuts);
       build.ExplicitDeps = std::move(ninjaDeps);
       build.OrderOnlyDeps = orderOnlyDeps;
       gg->WriteBuild(this->GetImplFileStream(fileConfig), build);
diff --git a/Source/cmLocalNinjaGenerator.h b/Source/cmLocalNinjaGenerator.h
index a73fa27..6404037 100644
--- a/Source/cmLocalNinjaGenerator.h
+++ b/Source/cmLocalNinjaGenerator.h
@@ -108,6 +108,7 @@ private:
                                        const std::string& config);
   void WriteNinjaFilesInclusionConfig(std::ostream& os);
   void WriteNinjaFilesInclusionCommon(std::ostream& os);
+  void WriteNinjaWorkDir(std::ostream& os);
   void WriteProcessedMakefile(std::ostream& os);
   void WritePools(std::ostream& os);
 
diff --git a/Source/cmNinjaTypes.h b/Source/cmNinjaTypes.h
index 320f41b..c8a411e 100644
--- a/Source/cmNinjaTypes.h
+++ b/Source/cmNinjaTypes.h
@@ -53,6 +53,7 @@ public:
   std::string Rule;
   cmNinjaDeps Outputs;
   cmNinjaDeps ImplicitOuts;
+  cmNinjaDeps WorkDirOuts; // For cmake_ninja_workdir.
   cmNinjaDeps ExplicitDeps;
   cmNinjaDeps ImplicitDeps;
   cmNinjaDeps OrderOnlyDeps;