Source sweep: Use cmStrCat for string concatenation

This patch is generated by a python script that uses regular expressions to
search for string concatenation patterns of the kind

```
std::string str = <ARG0>;
str += <ARG1>;
str += <ARG2>;
...
```

and replaces them with a single `cmStrCat` call

```
std::string str = cmStrCat(<ARG0>, <ARG1>, <ARG2>, ...);
```

If any `<ARGX>` is itself a concatenated string of the kind

```
a + b + c + ...;
```

then `<ARGX>` is split into multiple arguments for the `cmStrCat` call.

If there's a sequence of literals in the `<ARGX>`, then all literals in the
sequence are concatenated and merged into a single literal argument for
the `cmStrCat` call.

Single character strings are converted to single char arguments for
the `cmStrCat` call.

`std::to_string(...)` wrappings are removed from `cmStrCat` arguments,
because it supports numeric types as well as string types.

`arg.substr(x)` arguments to `cmStrCat` are replaced with
`cm::string_view(arg).substr(x)`

1 files changed, 3 insertions, 2 deletions

diff --git a/Source/cmSubdirCommand.cxx b/Source/cmSubdirCommand.cxx
index 9d36228..07f8efe 100644
--- a/Source/cmSubdirCommand.cxx
+++ b/Source/cmSubdirCommand.cxx
@@ -3,6 +3,7 @@
 #include "cmSubdirCommand.h"
 
 #include "cmMakefile.h"
+#include "cmStringAlgorithms.h"
 #include "cmSystemTools.h"
 
 class cmExecutionStatus;
@@ -44,8 +45,8 @@ bool cmSubdirCommand::InitialPass(std::vector<std::string> const& args,
         cmSystemTools::GetFilenameName(i);
       this->Makefile->AddSubDirectory(i, binPath, excludeFromAll, false);
     } else {
-      std::string error = "Incorrect SUBDIRS command. Directory: ";
-      error += i + " does not exist.";
+      std::string error = cmStrCat("Incorrect SUBDIRS command. Directory: ", i,
+                                   " does not exist.");
       this->SetError(error);
       res = false;
     }