Fix strict mode for nested calls and align the parser with R operators - #7

Follows up on obiba/datashield4j#8, which fixes operator handling in the Java parsers. DSLite has the same grammar bugs, but with different effects: it writes the AST back as infix text and R re-parses it, so wrong grouping never changed a result. The bugs only caused valid R to be rejected. Checking this also turned up a separate strict mode bypass.

Changes

Strict mode (R/DSLiteServer.R): replaceFunctionNode recursed through self$children, where self is the server rather than the node, so only the outermost call was checked and mapped. With f allowed, f(system('id')), 1 + system('id') and x = system('id') all passed. Nested calls are now checked and mapped.

Lexer and grammar (R/lex-yacc.R):

• - is no longer part of names, and signs are no longer part of numbers. a-f(1), a-(b), 1-1, x -1 and -1L now parse.
• ^, %*%, %%, %/% and unary + are supported in expressions.
• Precedence follows ?Syntax.
• The separate formula_term grammar is removed and ~ is an ordinary low-precedence operator. y-1 ~ x depended on - being part of names, so it would otherwise stop parsing. y ~ -x and y ~ x -1 now parse. Strings and function calls are still rejected in formulas.

Behaviour changes

• Scripts with nested calls that are not in the configured methods now fail in strict mode. This is the change most likely to affect downstream tests.
• -1 is now a UnaryOpNode rather than a NumericNode, and abc-DEF is a subtraction rather than a symbol. The evaluated result is unchanged, but code inspecting the AST would see the difference.
• a-b is emitted as a - b.

Testing

• The testthat suite passes, with new tests for nested strict mode checks, minus handling, precedence, % operators, formulas and the round trip through R's parser.
• 3,768 random arithmetic expressions: all now match parse() after the round trip. Before, 1,923 matched and 1,845 were rejected. None differed silently, before or after.
• 2,969 random formulas: all match parse(), run after the change only. These comparisons were one-off scripts and are not part of this PR.
• Not run: R CMD check and the dsBaseClient test suite.

Not addressed

These are valid R and are still rejected: comparison and logical operators, subsetting (a[1]), one-sided formulas (~ x) and .5. f(D$x = 1) still gets past the DSLite parser and is rejected later by parse().