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* ADR-045 string declarations: E0862-E0866.
*
* #1322. Fourteen throws in `StringDeclHelper`, all reaching the user as `1:0`.
*
* ## Three messages that were one rule
*
* At file scope a string may be initialized by a LITERAL and by nothing else.
* C has no place to run `strncpy` or `strncat` before `main`, so a copy from a
* variable, a concatenation and a substring extraction are all impossible
* there -- and all three threw, with three different messages, from three
* different generation paths. Probed rather than assumed: a literal and an
* absent initializer are accepted at file scope; those three are not.
*
* Written as one question about the initializer's FORM, the three collapse.
*
* ## Capacity is asked of the declaration, not of codegen
*
* The capacity rules -- an array needs `string<N>[M]`, a non-const needs
* `string<N>`, a const without one needs a literal to infer from -- are all
* properties of the declaration's own syntax. The fit rules need a source
* capacity, which is `IDeclaredVar.stringCapacity`: a literal's is its length,
* a variable's is what its declaration said.
*
* `CodeGenState.inFunctionBody` is what codegen asked for the file-scope
* question. It is a generation-time cursor and does not exist when this pass
* runs; the parse tree answers the same question by position.
*/
import { ParserRuleContext, ParseTreeWalker } from "antlr4ng";
import { CNextListener } from "../../PARSE/2-Parse/grammar/CNextListener";
import * as Parser from "../../PARSE/2-Parse/grammar/CNextParser";
import ExpressionUnwrapper from "../../utils/ExpressionUnwrapper";
import ParserUtils from "../../utils/ParserUtils";
import StringUtils from "../../utils/StringUtils";
import OperandTyper from "../../utils/OperandTyper";
import IStringDeclarationError from "./types/IStringDeclarationError";
import ConstantExpression from "./helpers/ConstantExpression";
import type IAnalysisContext from "./types/IAnalysisContext";
/** What a string-valued expression can hold, or null if it is not one. */
interface IStringSource {
readonly capacity: number;
readonly isLiteral: boolean;
}
class StringDeclarationListener extends CNextListener {
private readonly found: IStringDeclarationError[] = [];
public constructor(private readonly context: IAnalysisContext) {
super();
}
public errors(): IStringDeclarationError[] {
return this.found;
}
override enterVariableDeclaration = (
ctx: Parser.VariableDeclarationContext,
): void => {
const typeCtx = ctx.type();
const arrayType = typeCtx.arrayType?.();
const stringCtx = arrayType?.stringType?.() ?? typeCtx.stringType();
if (!stringCtx) return;
const isArray = arrayType?.stringType?.() !== undefined;
const declared = stringCtx.INTEGER_LITERAL();
const expression = ctx.expression();
const isConst = StringDeclarationListener.isConstDeclaration(ctx);
if (
!this.checkCapacityIsStated(
stringCtx,
declared,
isArray,
isConst,
expression,
)
) {
return;
}
if (declared === null) return; // an inferred const capacity always fits
const capacity = Number.parseInt(declared.getText(), 10);
if (!expression) return;
Iif (isArray) {
// #1322: a string ARRAY's initializer -- a list, of the declared size --
// is the same rule for every element type, and it is asked once, in
// `ArrayDeclarationAnalyzer` (ADR-035, E0866). The capacity rules below
// are about one string.
return;
}
if (!this.checkFileScopeForm(ctx, expression)) return;
this.checkFit(ctx, expression, capacity);
};
/**
* A declaration has to state a capacity, or be a `const` this pass can infer
* one from. Four throws, one question.
*/
private checkCapacityIsStated(
stringCtx: Parser.StringTypeContext,
declared: unknown,
isArray: boolean,
isConst: boolean,
expression: Parser.ExpressionContext | null,
): boolean {
if (declared !== null) return true;
if (isArray) {
this.report(
stringCtx,
"E0862",
"A string array requires an explicit capacity",
"Write the element capacity, e.g. string<64>[4].",
);
return false;
}
if (!isConst) {
this.report(
stringCtx,
"E0862",
"A non-const string requires an explicit capacity",
"Write the capacity, e.g. string<64>. Only a `const` can have one inferred.",
);
return false;
}
if (!expression) {
this.report(
stringCtx,
"E0862",
"A const string without a capacity requires an initializer to infer it from",
"Write the capacity, e.g. string<64>, or initialize it with a literal.",
);
return false;
}
if (StringDeclarationListener.literalOf(expression) === null) {
this.report(
expression,
"E0862",
"A const string without a capacity requires a string literal to infer it from",
"Write the capacity, e.g. string<64>. A capacity can only be inferred from a literal.",
);
return false;
}
return true;
}
/**
* At file scope a string may only be initialized by a literal.
*
* Returns false when it reported, so the fit checks below do not also fire on
* an initializer that cannot be there at all.
*/
private checkFileScopeForm(
ctx: Parser.VariableDeclarationContext,
expression: Parser.ExpressionContext,
): boolean {
if (StringDeclarationListener.isInsideFunction(ctx)) return true;
if (StringDeclarationListener.literalOf(expression) !== null) return true;
this.report(
expression,
"E0863",
`A string at file scope may only be initialized by a literal, not '${expression.getText()}'`,
"Copying, concatenating and extracting a substring all need runtime calls, which C cannot make before `main`. Move the declaration into a function, or initialize it empty and assign later.",
);
return false;
}
/** The initializer has to fit the declared capacity. */
private checkFit(
ctx: Parser.VariableDeclarationContext,
expression: Parser.ExpressionContext,
capacity: number,
): void {
const at: ParserRuleContext = ctx;
const substring = this.substringOf(expression, at);
if (substring !== null) {
this.checkSubstring(expression, substring, capacity);
return;
}
const concat = this.concatOf(expression, at);
if (concat !== null) {
const required = concat[0] + concat[1];
if (required > capacity) {
this.report(
expression,
"E0864",
`String concatenation requires capacity ${required}, but the declaration is string<${capacity}>`,
`Widen the declaration to string<${required}>, or shorten the operands.`,
);
}
return;
}
const source = this.stringSourceOf(expression, at);
Iif (source === null) return;
if (source.isLiteral && source.capacity > capacity) {
this.report(
expression,
"E0864",
`String literal (${source.capacity} chars) exceeds string<${capacity}> capacity`,
`Widen the declaration to string<${source.capacity}>, or shorten the literal.`,
);
return;
}
if (!source.isLiteral && source.capacity > capacity) {
this.report(
expression,
"E0864",
`Cannot initialize string<${capacity}> from string<${source.capacity}> -- the source may not fit`,
`Widen the declaration to string<${source.capacity}>, or extract a substring of the source.`,
);
}
}
private checkSubstring(
expression: Parser.ExpressionContext,
substring: {
start: number | null;
length: number | null;
sourceCapacity: number;
},
capacity: number,
): void {
const { start, length, sourceCapacity } = substring;
if (start !== null && length !== null && start + length > sourceCapacity) {
this.report(
expression,
"E0865",
`Substring bounds [${start}, ${length}] exceed the source string<${sourceCapacity}>`,
"The bounds are counted in characters from zero; keep start + length within the source's capacity.",
);
return;
}
if (length !== null && length > capacity) {
this.report(
expression,
"E0864",
`Substring length ${length} exceeds destination string<${capacity}> capacity`,
`Widen the declaration to string<${length}>, or take fewer characters.`,
);
}
}
// --- The facts the rules above are asked of ------------------------------
/** A string-valued expression's capacity: a literal's length, or a declared one. */
private stringSourceOf(
expression: Parser.ExpressionContext,
at: ParserRuleContext,
): IStringSource | null {
const literal = StringDeclarationListener.literalOf(expression);
if (literal !== null) {
return { capacity: StringUtils.literalLength(literal), isLiteral: true };
}
const name = expression.getText();
const capacity = this.capacityOfName(name, at);
return capacity === null ? null : { capacity, isLiteral: false };
}
/**
* A declared string's capacity, from this file's frames or the run-wide view.
*
* The name binds through Program's one binder (#1668), so a local still
* shadows an imported declaration, written once here rather than at each
* of the three places that ask.
*/
private capacityOfName(name: string, at: ParserRuleContext): number | null {
Iif (!/^[A-Za-z_]\w*$/.test(name)) return null;
const t = OperandTyper.typeOfName(name, at, this.context);
return t !== null && t.dimensions.length === 0 ? t.stringCapacity : null;
}
/** `left + right` where BOTH operands are strings, as their capacities. */
private concatOf(
expression: Parser.ExpressionContext,
at: ParserRuleContext,
): [number, number] | null {
const additive = ExpressionUnwrapper.getAdditiveExpression(expression);
Iif (!additive) return null;
const operands = additive.multiplicativeExpression();
// Exactly two operands, joined by `+` -- a `-` is not a concatenation, and
// the token is checked rather than the text, which would match a hyphen
// inside an identifier or a literal.
if (operands.length !== 2 || additive.MINUS().length > 0) return null;
const left = this.capacityOfOperand(operands[0], at);
const right = this.capacityOfOperand(operands[1], at);
return left !== null && right !== null ? [left, right] : null;
}
private capacityOfOperand(
operand: ParserRuleContext,
at: ParserRuleContext,
): number | null {
const text = operand.getText();
if (text.startsWith('"') && text.endsWith('"')) {
return StringUtils.literalLength(text);
}
return this.capacityOfName(text, at);
}
/** `src[start, length]`, or `src[i]` which is sugar for `src[i, 1]`. */
private substringOf(
expression: Parser.ExpressionContext,
at: ParserRuleContext,
): {
start: number | null;
length: number | null;
sourceCapacity: number;
} | null {
const postfix = ExpressionUnwrapper.getPostfixExpression(expression);
if (!postfix) return null;
const ops = postfix.postfixOp();
if (ops.length !== 1) return null;
const sourceName = postfix.primaryExpression()?.IDENTIFIER()?.getText();
Iif (!sourceName) return null;
const capacity = this.capacityOfName(sourceName, at);
Iif (capacity === null) return null;
const subscripts = ops[0].expression();
Eif (subscripts.length === 2) {
return {
start: this.constantOf(subscripts[0]),
length: this.constantOf(subscripts[1]),
sourceCapacity: capacity,
};
}
if (subscripts.length === 1) {
// `src[i]` is one character, which ADR-045 defines as `src[i, 1]`.
return {
start: this.constantOf(subscripts[0]),
length: 1,
sourceCapacity: capacity,
};
}
return null;
}
// --- Static helpers -------------------------------------------------------
/** The string literal an expression IS, or null. */
private static literalOf(
expression: Parser.ExpressionContext,
): string | null {
const text = expression.getText();
return text.startsWith('"') && text.endsWith('"') && text.length >= 2
? text
: null;
}
private static isConstDeclaration(
ctx: Parser.VariableDeclarationContext,
): boolean {
// Ask the grammar, not the text. The rule orders the modifiers
// `atomicModifier? volatileModifier? constModifier?`, so the text of
// `volatile const string s <- "x"` begins with the volatile keyword and a
// `startsWith("const")` test read it as NON-const -- rejecting valid
// C-Next with E0862 ("a non-const string requires an explicit capacity")
// on a declaration that is const. Every `atomic`/`volatile` unsized string was unreachable,
// which is also what hid the qualifier drop in `StringDeclHelper`'s
// unsized arm: nothing could get there to expose it.
//
// `VariableModifierBuilder.build` already asked this way; this was the
// second derivation of one predicate, and the text one was the wrong one.
return ctx.constModifier() !== null;
}
/**
* Whether the declaration sits inside a function body.
*
* `CodeGenState.inFunctionBody` is the generation-time cursor codegen asked;
* position in the tree is the same fact, available now.
*/
private static isInsideFunction(ctx: ParserRuleContext): boolean {
let node: ParserRuleContext | null = ctx.parent;
while (node) {
if (node instanceof Parser.FunctionDeclarationContext) return true;
node = node.parent;
}
return false;
}
/**
* #1322 review: the flat const map answers "whichever scope declared this
* name last". A string index or slice bound named by a scoped const was
* measured against the wrong one; `ConstantExpression` asks from where the
* bound is written, locals included.
*/
private constantOf(expr: Parser.ExpressionContext): number | null {
return ConstantExpression.valueAt(expr, this.context);
}
private report(
at: ParserRuleContext,
code: string,
message: string,
helpText: string,
): void {
const { line, column } = ParserUtils.getPosition(at);
this.found.push({ code, line, column, message, helpText });
}
}
class StringDeclarationAnalyzer {
/** #1456: handed in rather than read off shared state. */
constructor(private readonly context: IAnalysisContext) {}
public analyze(tree: Parser.ProgramContext): IStringDeclarationError[] {
const listener = new StringDeclarationListener(this.context);
ParseTreeWalker.DEFAULT.walk(listener, tree);
return listener.errors();
}
}
export default StringDeclarationAnalyzer;
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