From f34dd20fb7578874925dacf21b32338af50e8c12 Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Wed, 9 Nov 2022 10:59:36 +0200
Subject: Improve low-level diagnostics in `in` rule (and derived)

---
 libbuild2/in/rule.cxx   | 30 +++++++++++++++++++++++++++++-
 libbuild2/in/target.cxx | 10 +++++++++-
 2 files changed, 38 insertions(+), 2 deletions(-)

diff --git a/libbuild2/in/rule.cxx b/libbuild2/in/rule.cxx
index d07adfc..07c11c6 100644
--- a/libbuild2/in/rule.cxx
+++ b/libbuild2/in/rule.cxx
@@ -299,7 +299,35 @@ namespace build2
       if (verb >= 2)
         text << program_ << ' ' << ip << " >" << tp;
       else if (verb)
-        text << program_ << ' ' << ip;
+      {
+        // If we straight print the target, in most cases we will end up with
+        // something ugly like in{version...h.in} (due to the in{} target
+        // type search semantics). There is the `...h` part but also the
+        // `.in` part that is redundant given in{}. So let's tidy this up
+        // a bit if the extension could have been derived by in_search().
+        //
+        target_key ik (i.key ());
+
+        if (ik.ext)
+        {
+          string& ie (*ik.ext);
+          const string* te (t.ext ());
+
+          size_t in (ie.size ());
+          size_t tn (te != nullptr ? te->size () : 0);
+
+          if (in == tn + (tn != 0 ? 1 : 0) + 2) // [<te>.]in
+          {
+            if (ie.compare (in - 2, 2, "in") == 0)
+            {
+              if (tn == 0 || (ie.compare (0, tn, *te) == 0 && ie[tn] == '.'))
+                ie.clear ();
+            }
+          }
+        }
+
+        text << program_ << ' ' << ik;
+      }
 
       // Read and process the file, one line at a time, while updating depdb.
       //
diff --git a/libbuild2/in/target.cxx b/libbuild2/in/target.cxx
index d548453..54130ff 100644
--- a/libbuild2/in/target.cxx
+++ b/libbuild2/in/target.cxx
@@ -20,6 +20,14 @@ namespace build2
 
       if (!e)
       {
+        // Why is the extension, say, .h.in and not .in (with .h being in the
+        // name)? While this is mostly academic (in this case things will work
+        // the same either way), conceptually, it is a header template rather
+        // than some file template. In other words, we are adding the second
+        // level classification.
+        //
+        // See also the low verbosity tidying up code in the rule.
+        //
         if (const file* t = xt.is_a<file> ())
         {
           const string& te (t->derive_extension ());
@@ -51,7 +59,7 @@ namespace build2
       &target_extension_none,
       nullptr, /* default_extension */   // Taken care of by search.
       &in_pattern,
-      &target_print_1_ext_verb,          // Same as file.
+      &target_print_1_ext_verb,          // Same as file (but see rule).
       &in_search,
       target_type::flag::none
     };
-- 
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