find_program: Fixes when the program has been overridden by executable

- ExternalProgramHolder has path() method while CustomTargetHolder and
  BuildTargetHolder have full_path().
- The returned ExternalProgramHolder's path() method was broken, because
  build.Executable object has no get_path() method, it needs the
  backend.
- find_program('overridden_prog', version : '>=1.0') was broken because
  it needs to execute the exe that is not yet built. Now assume the
  program has the (sub)project version.
- If the version check fails, interpreter uses
  ExternalProgramHolder.get_name() for the error message but
  build.Executable does not implement get_name() method.

1 files changed, 20 insertions, 0 deletions

diff --git a/docs/markdown/snippets/find_program.md b/docs/markdown/snippets/find_program.md
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index 0000000..d0bb64d
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+++ b/docs/markdown/snippets/find_program.md
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+## find_program: Fixes when the program has been overridden by executable
+
+When a program has been overridden by an executable, the returned object of
+find_program() had some issues:
+
+```meson
+# In a subproject:
+exe = executable('foo', ...)
+meson.override_find_program('foo', exe)
+
+# In main project:
+# The version check was crashing meson.
+prog = find_program('foo', version : '>=1.0')
+
+# This was crashing meson.
+message(prog.path())
+
+# New method to be consistent with built objects.
+message(prog.full_path())
+```