carbon-language/carbon-lang
1
0
Fork 0
mirror of https://github.com/carbon-language/carbon-lang.git synced 2026-10-05 22:02:55 +01:00
Code Issues Packages Projects Releases 10 Wiki Activity

Support for parsing expression patterns (#6977)

Browse Source 
When parsing a pattern, if we encounter something that isn't pattern
syntax, try parsing as an expression instead. We only need one-token
lookahead to distinguish pattern syntax from expression syntax.

Track a precedence group through pattern parsing so that we can allow
different kinds of expressions in a top-level pattern (such as the
operand of `let`) and in a nested pattern (such as a subpattern of a
tuple pattern or within grouping parens). For example, we do not allow
`case if ...`, and for now I've chosen to also not allow logical or
relational operators at the top level of a pattern, so `case 1 + 1` is
OK, but `case 1 == 1` and `case true and false` require parentheses.
This decision should be ratified or revisited by a design proposal.

Very basic check support is also provided, only sufficient to form an
`ExprPattern` instruction and nothing beyond that. For now, all pattern
matching against an `ExprPattern` fails with a TODO error. To support
that, I've switched from calling `BeginSubpattern` in the parent handler
of a pattern and `EndSubpatternAs*` in the pattern handler itself to
calling both functions in parent handlers, with `EndSubpattern`
converting an expression into an expression pattern where needed.

Depends on #6976.

Assisted-by: Gemini via Google Antigravity
This commit is contained in:
Richard Smith
2026-03-28 00:06:06 +00:00
committed by GitHub
parent 1ef35e8299
commit 181a592b8c
49 changed files with 679 additions and 210 deletions
Download Patch File Download Diff File Expand all files Collapse all files
toolchain/check/cpp/import.cpp
+6 -3
View File
@@ -1113,7 +1113,9 @@ static auto MakeImplicitParamPatternsBlockId(
auto param_info = MapParameterType(context, loc_id, param_type);
auto [type_inst_id, type_id] = param_info.type;
SemIR::ExprRegionId type_expr_region_id =
EndSubpatternAsExpr(context, type_inst_id);
ConsumeSubpatternExpr(context, type_inst_id);
EndEmptySubpattern(context);
if (!type_id.has_value()) {
context.TODO(loc_id,
@@ -1163,7 +1165,7 @@ static auto MakeParamPatternsBlockId(Context& context, SemIR::LocId loc_id,
ClangGetUnqualifiedTypePreserveNonNull(context, orig_param_type);
// Mark the start of a region of insts, needed for the type expression
// created later with the call of `EndSubpatternAsExpr()`.
// created later with the call of `ConsumeSubpatternExpr()`.
BeginSubpattern(context);
auto param_info = MapParameterType(context, loc_id, param_type);
auto [type_inst_id, type_id] = param_info.type;
@@ -1171,7 +1173,8 @@ static auto MakeParamPatternsBlockId(Context& context, SemIR::LocId loc_id,
// region that allows control flow in the type expression e.g. fn F(x: if C
// then i32 else i64).
SemIR::ExprRegionId type_expr_region_id =
EndSubpatternAsExpr(context, type_inst_id);
ConsumeSubpatternExpr(context, type_inst_id);
EndEmptySubpattern(context);
if (!type_id.has_value()) {
context.TODO(loc_id, llvm::formatv("Unsupported: parameter type: {0}",