Fix parsing of partial float literals

src/spinasm_lsp/parser.py

@@ -2,6 +2,8 @@
 
 from __future__ import annotations
 
+import contextlib
+
 import lsprotocol.types as lsp
 from asfv1 import fv1parse
 
@@ -64,10 +66,14 @@ def __next__(self) -> None:
         current_line_txt = self._source[self._current_line]
         current_symbol = self.parsed_symbol.txt
 
-        # Start at the current column to skip previous duplicates of the symbol
-        self._current_character = current_line_txt.index(
-            current_symbol, self._current_character
-        )
+        # Update the current parsed character. This can fail under rare circumstances,
+        # in which case we'll leave _current_character unchanged.
+        # See https://github.com/aazuspan/spinasm-lsp/issues/31
+        with contextlib.suppress(ValueError):
+            # Start at the current column to skip previous duplicates of the symbol
+            self._current_character = current_line_txt.index(
+                current_symbol, self._current_character
+            )
 
 
 class SPINAsmDiagnosticParser(SPINAsmPositionParser):

tests/test_parser.py

@@ -46,3 +46,26 @@ def test_example_patches(patch, data_regression):
     encoded = serialize_parser_output(parser)
 
     data_regression.check(encoded)
+
+
+def test_parsing_as_typed():
+    """Test that the parser is fault tolerant for partially entered programs."""
+
+    # Example program from SPINAsm documentation. Iteratively parsing at each character
+    # is slow, so we use a small sample program here rather than parameterizing over the
+    # larger test patches.
+    source = """
+    ; Example program from SPINAsm documentation
+    Attn EQU 0.5
+    Tmp_Reg EQU 63
+    Tmp_Del EQU $2000
+
+    sof 0,0
+    rda Tmp_Del,Attn
+    wrax Tmp_Reg,1.0
+    wrax DACL
+    """
+    source_chars = list(source)
+    for i in range(len(source_chars)):
+        partial_source = "".join(source_chars[:i])
+        assert SPINAsmParser(partial_source)