another long-overdue bugfix

If I forgot a 'var', Mu would interpret the ':' in the var declaration
as a named block, and all parsing after would be thrown off.

Perhaps I should use separate characters for defining blocks vs vars.

linux/mu.subx

@@ -1988,6 +1988,50 @@ test-stmt-with-unknown-var:
     5d/pop-to-ebp
     c3/return
 
+test-stmt-with-missing-var-keyword:
+    # . prologue
+    55/push-ebp
+    89/<- %ebp 4/r32/esp
+    # setup
+    (clear-stream _test-input-stream)
+    (clear-stream $_test-input-buffered-file->buffer)
+    (clear-stream _test-output-stream)
+    (clear-stream $_test-output-buffered-file->buffer)
+    (clear-stream _test-error-stream)
+    (clear-stream $_test-error-buffered-file->buffer)
+    # var ed/edx: exit-descriptor = tailor-exit-descriptor(16)
+    68/push 0/imm32
+    68/push 0/imm32
+    89/<- %edx 4/r32/esp
+    (tailor-exit-descriptor %edx 0x10)
+    #
+    (write _test-input-stream "fn foo {\n")
+    (write _test-input-stream "  x: int\n")
+    (write _test-input-stream "}\n")
+    # convert
+    (convert-mu _test-input-buffered-file _test-output-buffered-file _test-error-buffered-file %edx)
+    # registers except esp clobbered at this point
+    # restore ed
+    89/<- %edx 4/r32/esp
+    (flush _test-output-buffered-file)
+    (flush _test-error-buffered-file)
+#?     # dump _test-error-stream {{{
+#?     (write 2 "^")
+#?     (write-stream 2 _test-error-stream)
+#?     (write 2 "$\n")
+#?     (rewind-stream _test-error-stream)
+#?     # }}}
+    # check output
+    (check-stream-equal _test-output-stream  ""  "F - test-stmt-with-missing-var-keyword: output should be empty")
+    (check-next-stream-line-equal _test-error-stream  "fn foo: unexpected ':'; did you forget a 'var'?"  "F - test-stmt-with-missing-var-keyword: error message")
+    # check that stop(1) was called
+    (check-ints-equal *(edx+4) 2 "F - test-stmt-with-missing-var-keyword: exit status")
+    # don't restore from ebp
+    81 0/subop/add %esp 8/imm32
+    # . epilogue
+    5d/pop-to-ebp
+    c3/return
+
 test-stmt-with-invalid-identifier:
     # . prologue
     55/push-ebp
@@ -18204,7 +18248,8 @@ parse-mu-block:  # in: (addr buffered-file), vars: (addr stack live-var), fn: (a
     #     else if slice-equal?(word-slice, "}")
     #       break
     #     else if slice-ends-with?(word-slice, ":")
-    #       # TODO: error-check the rest of 'line'
+    #       if !slice-equal?(next-mu-token(line), "{")
+    #         abort
     #       --word-slice->end to skip ':'
     #       named-block = parse-mu-named-block(word-slice, in, vars, fn)
     #       append-to-block(out-addr, named-block)
@@ -18320,8 +18365,8 @@ $parse-mu-block:check-for-named-block:
         # . if (eax != ':') break
         3d/compare-eax-and 0x3a/imm32/colon
         0f 85/jump-if-!= break/disp32
-        # TODO: error-check the rest of 'line'
-        #
+        # if next-mu-token(line) != "{", abort
+        (check-next-token-is-open-curly %ecx *(ebp+0x10) *(ebp+0x18) *(ebp+0x1c))
         # skip ':'
         ff 1/subop/decrement *(edx+4)  # Slice-end
         # var tmp/eax: (handle block)
@@ -18399,6 +18444,45 @@ $parse-mu-block:abort:
     (stop *(ebp+0x1c) 1)
     # never gets here
 
+check-next-token-is-open-curly:  # line: (addr stream byte), fn: (addr function), err: (addr buffered-file), ed: (addr exit-descriptor)
+    # . prologue
+    55/push-ebp
+    89/<- %ebp 4/r32/esp
+    # . save registers
+    50/push-eax
+    52/push-edx
+    # var word-slice/edx: slice
+    68/push 0/imm32/end
+    68/push 0/imm32/start
+    89/<- %edx 4/r32/esp
+    # word-slice = next-mu-token(line)
+    (next-mu-token *(ebp+8) %edx)
+    # if !slice-equal?(word-slice, "{") abort
+    (slice-equal? %edx "{")  # => eax
+    3d/compare-eax-and 0/imm32/false
+    0f 84/jump-if-= $check-next-token-is-open-curly:abort/disp32
+$check-next-token-is-open-curly:end:
+    # . reclaim locals
+    81 0/subop/add %esp 8/imm32
+    # . restore registers
+    5a/pop-to-edx
+    58/pop-to-eax
+    # . epilogue
+    89/<- %esp 5/r32/ebp
+    5d/pop-to-ebp
+    c3/return
+
+$check-next-token-is-open-curly:abort:
+    # error("fn " fn ": unexpected ':'; did you forget a 'var'?")
+    (write-buffered *(ebp+0x10) "fn ")
+    8b/-> *(ebp+0xc) 0/r32/eax
+    (lookup *eax *(eax+4))  # Function-name Function-name => eax
+    (write-buffered *(ebp+0x10) %eax)
+    (write-buffered *(ebp+0x10) ": unexpected ':'; did you forget a 'var'?\n")
+    (flush *(ebp+0x10))
+    (stop *(ebp+0x14) 1)
+    # never gets here
+
 new-block-name:  # fn: (addr function), out: (addr handle var)
     # . prologue
     55/push-ebp