From 120722059c8612fb13d7bf585a5593582a49220d Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Fri, 17 Mar 2017 11:09:36 +0200
Subject: Implement alternative command line buildspec and variable assignment
 syntax

b test: foo/ bar/
b config.import.libhello = ../libhello/
---
 build2/b.cli | 29 ++++++++++++++++++++++++++++
 build2/b.cxx | 62 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 89 insertions(+), 2 deletions(-)

diff --git a/build2/b.cli b/build2/b.cli
index 0d345bf..f1fd7dc 100644
--- a/build2/b.cli
+++ b/build2/b.cli
@@ -87,6 +87,26 @@ namespace build2
      b '{clean disfigure}(...)'     # similar to distclean
      \
 
+     In POSIX shells parenthesis are special characters and must be quoted
+     when used in a buildspec. Besides being an inconvenience in itself,
+     quoting also inhibits path auto-completion. To help with this situation a
+     shortcut syntax is available for executing a single operation or
+     meta-operation, for example:
+
+     \
+     b clean: foo/ bar/                # clean(foo/ bar/)
+     b configure: src/@out/            # configure(src/@out/)
+     b create: conf/, cxx              # create(conf/, cxx)
+     b configure: config.cxx=g++ src/  # configure(src/) config.cxx=g++
+     \
+
+     To activate the shortcut syntax the first buildspec argument must start
+     with an operation or meta-operation name and end with a colon (\cb{:}).
+     To transform the shortcut syntax to the normal buildspec syntax the colon
+     is replaced with the opening parenthesis (\cb{(}), the rest of the
+     buildspec arguments are treated as is, and the final closing parenthesis
+     (\cb{)}) is added.
+
      For each <target> the driver expects to find \cb{buildfile} either in the
      target's directory or, if the directory is part of the \cb{out} tree
      (\cb{out_base}), in the corresponding \cb{src} directory (\cb{src_base}).
@@ -142,6 +162,15 @@ namespace build2
      b config.cxx=clang++ config.cxx.coptions=-O3
      \
 
+     Similar to buildspec, POSIX shells often inhibit path auto-completion on
+     the right hand side of a variable assignment. To help with this situation
+     the assignment can be broken down into three separate command line
+     arguments, for example:
+
+     \
+     b config.import.libhello = ../libhello/
+     \
+
      The build system has the following built-in and pre-defined
      meta-operations:
 
diff --git a/build2/b.cxx b/build2/b.cxx
index d2ad368..1f0464f 100644
--- a/build2/b.cxx
+++ b/build2/b.cxx
@@ -117,6 +117,9 @@ main (int argc, char* argv[])
     {
       cl::argv_scanner scan (argc, argv);
 
+      size_t argn (0);       // Argument count.
+      bool shortcut (false); // True if the shortcut syntax is used.
+
       for (bool opt (true), var (true); scan.more (); )
       {
         if (opt)
@@ -159,12 +162,43 @@ main (int argc, char* argv[])
             continue;
           }
 
-          if (strchr (s, '=') != nullptr) // Covers =, +=, and =+.
+          if (const char* p = strchr (s, '=')) // Covers =, +=, and =+.
           {
+            // Diagnose the empty variable name situation. Note that we don't
+            // allow "partially broken down" assignments (as in foo =bar)
+            // since foo= bar would be ambigous.
+            //
+            if (p == s || (p == s + 1 && *s == '+'))
+              fail << "missing variable name in '" << s << "'";
+
             cmd_vars.push_back (s);
             continue;
           }
 
+          // Handle the "broken down" variable assignments (i.e., foo = bar
+          // instead of foo=bar).
+          //
+          if (scan.more ())
+          {
+            const char* a (scan.peek ());
+
+            if (strcmp (a, "=" ) == 0 ||
+                strcmp (a, "+=") == 0 ||
+                strcmp (a, "=+") == 0)
+            {
+              string v (s);
+              v += a;
+
+              scan.next ();
+
+              if (scan.more ())
+                v += scan.next ();
+
+              cmd_vars.push_back (move (v));
+              continue;
+            }
+          }
+
           // Fall through.
         }
 
@@ -174,10 +208,34 @@ main (int argc, char* argv[])
         // diagnostics (i.e., we could have used <buildspec-1>, <buildspec-2>
         // to give the idea about which argument is invalid).
         //
-        if (!args.empty ())
+        // Or we could separate arguments with newlines so that a line number
+        // signifies the argument number.
+        //
+        if (argn != 0)
           args += ' ';
 
         args += s;
+
+        // See if we are using the shortcut syntax.
+        //
+        if (argn == 0 && args.back () == ':')
+        {
+          args.back () = '(';
+          shortcut = true;
+        }
+
+        argn++;
+      }
+
+      // Add the closing parenthesis unless there wasn't anything in between
+      // in which case pop the opening one.
+      //
+      if (shortcut)
+      {
+        if (argn == 1)
+          args.pop_back ();
+        else
+          args += ')';
       }
     }
     catch (const cl::exception& e)
-- 
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