target_sources: Interpret relative paths as relative to the calling directory

Previously the command considered non-absolute source file paths relative to
the associated target on the LHS. This causes problems in incremental builds
where files are added from subdirectories and forces users to workaround by
manually converting to absolute paths. Change this to enable more intuitive
usage by projects.

Fixes #17981

3 files changed, 101 insertions, 3 deletions

diff --git a/Source/cmPolicies.h b/Source/cmPolicies.h
index 3fe0c84..1732ad6 100644
--- a/Source/cmPolicies.h
+++ b/Source/cmPolicies.h
@@ -223,7 +223,10 @@ class cmMakefile;
          12, 0, cmPolicies::WARN)                                             \
   SELECT(POLICY, CMP0075,                                                     \
          "Include file check macros honor CMAKE_REQUIRED_LIBRARIES.", 3, 12,  \
-         0, cmPolicies::WARN)
+         0, cmPolicies::WARN)                                                 \
+  SELECT(POLICY, CMP0076,                                                     \
+         "target_sources() command converts relative paths to absolute.", 3,  \
+         13, 0, cmPolicies::WARN)
 
 #define CM_SELECT_ID(F, A1, A2, A3, A4, A5, A6) F(A1)
 #define CM_FOR_EACH_POLICY_ID(POLICY)                                         \
@@ -248,7 +251,8 @@ class cmMakefile;
   F(CMP0065)                                                                  \
   F(CMP0068)                                                                  \
   F(CMP0069)                                                                  \
-  F(CMP0073)
+  F(CMP0073)                                                                  \
+  F(CMP0076)
 
 /** \class cmPolicies
  * \brief Handles changes in CMake behavior and policies
diff --git a/Source/cmTargetSourcesCommand.cxx b/Source/cmTargetSourcesCommand.cxx
index 3dd3748..62e323c 100644
--- a/Source/cmTargetSourcesCommand.cxx
+++ b/Source/cmTargetSourcesCommand.cxx
@@ -2,10 +2,14 @@
    file Copyright.txt or https://cmake.org/licensing for details.  */
 #include "cmTargetSourcesCommand.h"
 
+#include <cstring>
 #include <sstream>
 
 #include "cmAlgorithms.h"
+#include "cmGeneratorExpression.h"
 #include "cmMakefile.h"
+#include "cmPolicies.h"
+#include "cmSystemTools.h"
 #include "cmTarget.h"
 #include "cmake.h"
 
@@ -17,6 +21,14 @@ bool cmTargetSourcesCommand::InitialPass(std::vector<std::string> const& args,
   return this->HandleArguments(args, "SOURCES");
 }
 
+void cmTargetSourcesCommand::HandleInterfaceContent(
+  cmTarget* tgt, const std::vector<std::string>& content, bool prepend,
+  bool system)
+{
+  cmTargetPropCommandBase::HandleInterfaceContent(
+    tgt, ConvertToAbsoluteContent(tgt, content, true), prepend, system);
+}
+
 void cmTargetSourcesCommand::HandleMissingTarget(const std::string& name)
 {
   std::ostringstream e;
@@ -35,6 +47,79 @@ std::string cmTargetSourcesCommand::Join(
 bool cmTargetSourcesCommand::HandleDirectContent(
   cmTarget* tgt, const std::vector<std::string>& content, bool, bool)
 {
-  tgt->AppendProperty("SOURCES", this->Join(content).c_str());
+  tgt->AppendProperty(
+    "SOURCES",
+    this->Join(ConvertToAbsoluteContent(tgt, content, false)).c_str());
   return true; // Successfully handled.
 }
+
+std::vector<std::string> cmTargetSourcesCommand::ConvertToAbsoluteContent(
+  cmTarget* tgt, const std::vector<std::string>& content,
+  bool isInterfaceContent)
+{
+  // Skip conversion in case old behavior has been explictly requested
+  if (this->Makefile->GetPolicyStatus(cmPolicies::CMP0076) ==
+      cmPolicies::OLD) {
+    return content;
+  }
+
+  bool changedPath = false;
+  std::vector<std::string> absoluteContent;
+  absoluteContent.reserve(content.size());
+  for (std::string const& src : content) {
+    std::string absoluteSrc;
+    if (cmSystemTools::FileIsFullPath(src) ||
+        cmGeneratorExpression::Find(src) == 0 ||
+        (!isInterfaceContent &&
+         strcmp(this->Makefile->GetCurrentSourceDirectory(),
+                tgt->GetMakefile()->GetCurrentSourceDirectory()) == 0)) {
+      absoluteSrc = src;
+    } else {
+      changedPath = true;
+      absoluteSrc = this->Makefile->GetCurrentSourceDirectory();
+      absoluteSrc += "/";
+      absoluteSrc += src;
+    }
+    absoluteContent.push_back(absoluteSrc);
+  }
+
+  if (!changedPath) {
+    return content;
+  }
+
+  bool issueMessage = true;
+  bool useAbsoluteContent = false;
+  std::ostringstream e;
+  switch (this->Makefile->GetPolicyStatus(cmPolicies::CMP0076)) {
+    case cmPolicies::WARN:
+      e << cmPolicies::GetPolicyWarning(cmPolicies::CMP0076) << "\n";
+      break;
+    case cmPolicies::OLD:
+      issueMessage = false;
+      break;
+    case cmPolicies::REQUIRED_ALWAYS:
+    case cmPolicies::REQUIRED_IF_USED:
+      this->Makefile->IssueMessage(
+        cmake::FATAL_ERROR,
+        cmPolicies::GetRequiredPolicyError(cmPolicies::CMP0076));
+      break;
+    case cmPolicies::NEW: {
+      issueMessage = false;
+      useAbsoluteContent = true;
+      break;
+    }
+  }
+
+  if (issueMessage) {
+    if (isInterfaceContent) {
+      e << "An interface source of target \"" << tgt->GetName()
+        << "\" has a relative path.";
+    } else {
+      e << "A private source from a directory other than that of target \""
+        << tgt->GetName() << "\" has a relative path.";
+    }
+    this->Makefile->IssueMessage(cmake::AUTHOR_WARNING, e.str());
+  }
+
+  return useAbsoluteContent ? absoluteContent : content;
+}
diff --git a/Source/cmTargetSourcesCommand.h b/Source/cmTargetSourcesCommand.h
index ea8776a..b01e3ca 100644
--- a/Source/cmTargetSourcesCommand.h
+++ b/Source/cmTargetSourcesCommand.h
@@ -29,6 +29,11 @@ public:
   bool InitialPass(std::vector<std::string> const& args,
                    cmExecutionStatus& status) override;
 
+protected:
+  void HandleInterfaceContent(cmTarget* tgt,
+                              const std::vector<std::string>& content,
+                              bool prepend, bool system) override;
+
 private:
   void HandleMissingTarget(const std::string& name) override;
 
@@ -37,6 +42,10 @@ private:
                            bool prepend, bool system) override;
 
   std::string Join(const std::vector<std::string>& content) override;
+
+  std::vector<std::string> ConvertToAbsoluteContent(
+    cmTarget* tgt, const std::vector<std::string>& content,
+    bool isInterfaceContent);
 };
 
 #endif