Don't allow invalid interpolations to occur (#1925)

Fixes #1921

test/asm/invalid-format.err

@@ -12,9 +12,9 @@ error: STRFMT: Invalid format spec for argument 2
     at invalid-format.asm(5)
 error: STRFMT: Invalid format spec for argument 3
     at invalid-format.asm(5)
-error: Invalid format spec "5d5"
+error: Invalid interpolation format spec "5d5"
     at invalid-format.asm(8)
-error: Invalid format spec "xx"
+error: Invalid interpolation format spec "xx"
     at invalid-format.asm(9)
 error: Formatting string with sign flag '+'
     at invalid-format.asm(11)

test/asm/invalid-format.out

@@ -3,8 +3,8 @@ $2a %##x
 42   %--4d
 42 %..f
 42.00000 %q.16f %qq16f
-   42    42
-2a 2a
+   42 
+2a 
 hello
 hello
 hello

test/asm/label-macro-arg.err

@@ -10,8 +10,6 @@ error: syntax error, unexpected label, expecting symbol
     while expanding symbol `VAR_DEF`
 error: syntax error, unexpected label, expecting symbol
     at label-macro-arg.asm::test_char(26) <- label-macro-arg.asm(39)
-error: Invalid format spec "sizeof_"
+error: Invalid interpolation format spec "sizeof_"
     at label-macro-arg.asm::test_char(29) <- label-macro-arg.asm(39)
-error: Interpolated symbol `something` does not exist
-    at label-macro-arg.asm::test_char(29) <- label-macro-arg.asm(39)
-Assembly aborted with 7 errors
+Assembly aborted with 6 errors

test/asm/nested-brackets.err

@@ -1,3 +1,3 @@
-error: Missing '}'
+error: Unterminated interpolation
     at nested-brackets.asm(5)
 Assembly aborted with 1 error

test/asm/nested-brackets.out

@@ -1,2 +1,2 @@
 OK
-OK
+

test/asm/unterminated-interpolation.asm

@@ -0,0 +1,13 @@
+def x = 10
+println "{d:x", "!"
+println "{v:x", "?"
+println x, {d:x
+
+def name equs "x"
+println "{{name", "..."
+println "{v:{name}}!"
+println "{v:{name}?"
+println "{v:{name}", "?"
+println "{d:{v:name}}!?"
+println "{d:{v:name}?!"
+println "{d:{v:name}", "?!"

test/asm/unterminated-interpolation.err

@@ -0,0 +1,36 @@
+error: Unterminated interpolation
+    at unterminated-interpolation.asm(2)
+error: Invalid interpolation format spec "v"
+    at unterminated-interpolation.asm(3)
+error: Unterminated interpolation
+    at unterminated-interpolation.asm(3)
+error: Unterminated interpolation
+    at unterminated-interpolation.asm(4)
+error: Unterminated interpolation
+    at unterminated-interpolation.asm(7)
+error: Unterminated interpolation
+    at unterminated-interpolation.asm(7)
+error: Invalid interpolation format spec "v"
+    at unterminated-interpolation.asm(8)
+error: Invalid interpolation format spec "v"
+    at unterminated-interpolation.asm(9)
+error: Unterminated interpolation
+    at unterminated-interpolation.asm(9)
+error: Invalid interpolation format spec "v"
+    at unterminated-interpolation.asm(10)
+error: Unterminated interpolation
+    at unterminated-interpolation.asm(10)
+    while expanding symbol `name`
+error: Invalid interpolation format spec "v"
+    at unterminated-interpolation.asm(11)
+error: Interpolated symbol `` does not exist
+    at unterminated-interpolation.asm(11)
+error: Invalid interpolation format spec "v"
+    at unterminated-interpolation.asm(12)
+error: Unterminated interpolation
+    at unterminated-interpolation.asm(12)
+error: Invalid interpolation format spec "v"
+    at unterminated-interpolation.asm(13)
+error: Unterminated interpolation
+    at unterminated-interpolation.asm(13)
+Assembly aborted with 17 errors

test/asm/unterminated-interpolation.out

@@ -0,0 +1,10 @@
+!
+?
+$A
+...
+!
+
+?
+!?
+
+?!