Add support for 'T' transition snapshots, which are identical to S snapshots except they tell the makefile to stop at stage1.

Makefile.in

@@ -165,6 +165,25 @@ LLVM_AS := $(CFG_LLVM_BINDIR)/llvm-as
 # Single-target rules
 ######################################################################
 
+ifneq ($(CFG_IN_TRANSITION),)
+
+CFG_INFO := $(info cfg: *** compiler is in snapshot transition ***)
+CFG_INFO := $(info cfg: *** stage2 and later will not be built ***)
+
+all: rt/$(CFG_RUNTIME)          \
+     rustllvm/$(CFG_RUSTLLVM)   \
+     stage0/$(CFG_STDLIB)       \
+     stage0/intrinsics.bc       \
+     stage0/rustc$(X)           \
+     $(GENERATED)               \
+     $(DOCS)                    \
+     stage1/$(CFG_STDLIB)       \
+     stage1/intrinsics.bc       \
+     stage1/glue.o              \
+     stage1/rustc$(X)           \
+
+else
+
 all: rt/$(CFG_RUNTIME)          \
      rustllvm/$(CFG_RUSTLLVM)   \
      stage0/$(CFG_STDLIB)       \
@@ -185,12 +204,14 @@ all: rt/$(CFG_RUNTIME)          \
      stage3/intrinsics.bc       \
      stage3/rustc$(X)
 
+endif
+
 
 ######################################################################
 # Re-configuration
 ######################################################################
 
-config.mk: $(S)configure $(S)Makefile.in
+config.mk: $(S)configure $(S)Makefile.in $(S)src/snapshots.txt
 	@$(call E, cfg: reconfiguring)
 	$(S)configure $(CFG_CONFIGURE_ARGS)
 

configure

@@ -217,6 +217,12 @@ then
     err "either clang or gcc is required"
 fi
 
+if head -n 1 ${CFG_SRC_DIR}src/snapshots.txt | grep -q '^T'
+then
+    CFG_IN_TRANSITION=1
+    putvar CFG_IN_TRANSITION
+fi
+
 # Valgrind is only reliable on Linux. On Windows it doesn't work at all, and
 # on the Mac the dynamic linker causes Valgrind to emit a huge stream of
 # errors.

src/etc/get-snapshot.py

@@ -41,9 +41,6 @@ def determine_curr_snapshot_for_platform():
     parsed = parse_line(i, line)
     if (not parsed): continue
 
-    if parsed["type"] == "transition":
-      raise Exception("working on a transition, not updating stage0")
-
     if found_snap and parsed["type"] == "file":
       if parsed["platform"] == platform:
         hsh = parsed["hash"]

src/etc/snapshot.py

@@ -35,10 +35,7 @@ def parse_line(n, line):
   match = re.match(r"([ST]) (\d{4}-\d{2}-\d{2}) ([a-fA-F\d]+)\s*$", line);
   if (not match):
     raise Exception("%s:%d:E syntax error" % (snapshotfile, n))
-  ttype = "snapshot"
-  if (match.group(1) == "T"):
-    ttype = "transition"
-  return {"type": ttype,
+  return {"type": "snapshot",
           "date": match.group(2),
           "rev": match.group(3)}