From 60830e36e38f49bc797ae731c9dd58d7231039bf Mon Sep 17 00:00:00 2001
From: r00ster91 <r00ster91@proton.me>
Date: Fri, 21 Jul 2023 02:19:32 +0200
Subject: [PATCH 1/6] Sema error: talk about discarding instead of suppressing

Maybe I'm just being pedantic here (most likely) but I don't like how we're
just telling the user here how to "suppress this error" by "assigning the value to '_'".
I think it's better if we use the word "discard" here which I think is
the official terminology and also tells the user what it actually means
to "assign the value to '_'".

Also, using the value would also be a way to "suppress the error".
It is just one of the two options: discard or use.
---
 src/Sema.zig                                           |  2 +-
 .../for_loop_body_expression_ignored.zig               |  8 ++++----
 .../compile_errors/generic_instantiation_failure.zig   |  2 +-
 .../ignored_assert-err-ok_return_value.zig             |  2 +-
 .../ignored_comptime_statement_value.zig               |  2 +-
 test/cases/compile_errors/ignored_comptime_value.zig   |  4 ++--
 .../ignored_deferred_statement_value.zig               |  2 +-
 test/cases/compile_errors/ignored_return_value.zig     |  2 +-
 test/cases/compile_errors/ignored_statement_value.zig  |  2 +-
 .../while_loop_body_expression_ignored.zig             | 10 +++++-----
 10 files changed, 18 insertions(+), 18 deletions(-)

diff --git a/src/Sema.zig b/src/Sema.zig
index 37fdf0adb5..3ff817cbd1 100644
--- a/src/Sema.zig
+++ b/src/Sema.zig
@@ -3571,7 +3571,7 @@ fn ensureResultUsed(
                 const msg = try sema.errMsg(block, src, "value of type '{}' ignored", .{ty.fmt(sema.mod)});
                 errdefer msg.destroy(sema.gpa);
                 try sema.errNote(block, src, msg, "all non-void values must be used", .{});
-                try sema.errNote(block, src, msg, "this error can be suppressed by assigning the value to '_'", .{});
+                try sema.errNote(block, src, msg, "to discard the value, assign it to '_'", .{});
                 break :msg msg;
             };
             return sema.failWithOwnedErrorMsg(block, msg);
diff --git a/test/cases/compile_errors/for_loop_body_expression_ignored.zig b/test/cases/compile_errors/for_loop_body_expression_ignored.zig
index a0247139ea..9c5e381e63 100644
--- a/test/cases/compile_errors/for_loop_body_expression_ignored.zig
+++ b/test/cases/compile_errors/for_loop_body_expression_ignored.zig
@@ -23,13 +23,13 @@ export fn f4() void {
 //
 // :5:30: error: value of type 'usize' ignored
 // :5:30: note: all non-void values must be used
-// :5:30: note: this error can be suppressed by assigning the value to '_'
+// :5:30: note: to discard the value, assign it to '_'
 // :9:30: error: value of type 'usize' ignored
 // :9:30: note: all non-void values must be used
-// :9:30: note: this error can be suppressed by assigning the value to '_'
+// :9:30: note: to discard the value, assign it to '_'
 // :13:31: error: value of type 'bool' ignored
 // :13:31: note: all non-void values must be used
-// :13:31: note: this error can be suppressed by assigning the value to '_'
+// :13:31: note: to discard the value, assign it to '_'
 // :16:42: error: value of type 'usize' ignored
 // :16:42: note: all non-void values must be used
-// :16:42: note: this error can be suppressed by assigning the value to '_'
+// :16:42: note: to discard the value, assign it to '_'
diff --git a/test/cases/compile_errors/generic_instantiation_failure.zig b/test/cases/compile_errors/generic_instantiation_failure.zig
index 42e4c4e8c8..d820f8f410 100644
--- a/test/cases/compile_errors/generic_instantiation_failure.zig
+++ b/test/cases/compile_errors/generic_instantiation_failure.zig
@@ -24,4 +24,4 @@ pub export fn entry() void {
 //
 // :18:43: error: value of type 'type' ignored
 // :18:43: note: all non-void values must be used
-// :18:43: note: this error can be suppressed by assigning the value to '_'
+// :18:43: note: to discard the value, assign it to '_'
diff --git a/test/cases/compile_errors/ignored_assert-err-ok_return_value.zig b/test/cases/compile_errors/ignored_assert-err-ok_return_value.zig
index 1257636622..abe2b006b7 100644
--- a/test/cases/compile_errors/ignored_assert-err-ok_return_value.zig
+++ b/test/cases/compile_errors/ignored_assert-err-ok_return_value.zig
@@ -11,4 +11,4 @@ fn bar() anyerror!i32 {
 //
 // :2:11: error: value of type 'i32' ignored
 // :2:11: note: all non-void values must be used
-// :2:11: note: this error can be suppressed by assigning the value to '_'
+// :2:11: note: to discard the value, assign it to '_'
diff --git a/test/cases/compile_errors/ignored_comptime_statement_value.zig b/test/cases/compile_errors/ignored_comptime_statement_value.zig
index 2067f3b716..4dd0e0fc39 100644
--- a/test/cases/compile_errors/ignored_comptime_statement_value.zig
+++ b/test/cases/compile_errors/ignored_comptime_statement_value.zig
@@ -10,4 +10,4 @@ export fn foo() void {
 //
 // :3:9: error: value of type 'comptime_int' ignored
 // :3:9: note: all non-void values must be used
-// :3:9: note: this error can be suppressed by assigning the value to '_'
+// :3:9: note: to discard the value, assign it to '_'
diff --git a/test/cases/compile_errors/ignored_comptime_value.zig b/test/cases/compile_errors/ignored_comptime_value.zig
index 3414d0861f..ed7eb80b50 100644
--- a/test/cases/compile_errors/ignored_comptime_value.zig
+++ b/test/cases/compile_errors/ignored_comptime_value.zig
@@ -14,7 +14,7 @@ fn bar() u8 {
 //
 // :2:5: error: value of type 'comptime_int' ignored
 // :2:5: note: all non-void values must be used
-// :2:5: note: this error can be suppressed by assigning the value to '_'
+// :2:5: note: to discard the value, assign it to '_'
 // :5:5: error: value of type 'u8' ignored
 // :5:5: note: all non-void values must be used
-// :5:5: note: this error can be suppressed by assigning the value to '_'
+// :5:5: note: to discard the value, assign it to '_'
diff --git a/test/cases/compile_errors/ignored_deferred_statement_value.zig b/test/cases/compile_errors/ignored_deferred_statement_value.zig
index 1f42efc3f5..70b88a4deb 100644
--- a/test/cases/compile_errors/ignored_deferred_statement_value.zig
+++ b/test/cases/compile_errors/ignored_deferred_statement_value.zig
@@ -10,4 +10,4 @@ export fn foo() void {
 //
 // :3:9: error: value of type 'comptime_int' ignored
 // :3:9: note: all non-void values must be used
-// :3:9: note: this error can be suppressed by assigning the value to '_'
+// :3:9: note: to discard the value, assign it to '_'
diff --git a/test/cases/compile_errors/ignored_return_value.zig b/test/cases/compile_errors/ignored_return_value.zig
index 08424c4fe9..f721bc8655 100644
--- a/test/cases/compile_errors/ignored_return_value.zig
+++ b/test/cases/compile_errors/ignored_return_value.zig
@@ -11,4 +11,4 @@ fn bar() i32 {
 //
 // :2:8: error: value of type 'i32' ignored
 // :2:8: note: all non-void values must be used
-// :2:8: note: this error can be suppressed by assigning the value to '_'
+// :2:8: note: to discard the value, assign it to '_'
diff --git a/test/cases/compile_errors/ignored_statement_value.zig b/test/cases/compile_errors/ignored_statement_value.zig
index c73da84420..6c4ff442c5 100644
--- a/test/cases/compile_errors/ignored_statement_value.zig
+++ b/test/cases/compile_errors/ignored_statement_value.zig
@@ -8,4 +8,4 @@ export fn foo() void {
 //
 // :2:5: error: value of type 'comptime_int' ignored
 // :2:5: note: all non-void values must be used
-// :2:5: note: this error can be suppressed by assigning the value to '_'
+// :2:5: note: to discard the value, assign it to '_'
diff --git a/test/cases/compile_errors/while_loop_body_expression_ignored.zig b/test/cases/compile_errors/while_loop_body_expression_ignored.zig
index b3e83f202a..dae546df02 100644
--- a/test/cases/compile_errors/while_loop_body_expression_ignored.zig
+++ b/test/cases/compile_errors/while_loop_body_expression_ignored.zig
@@ -32,16 +32,16 @@ export fn f5() void {
 //
 // :5:25: error: value of type 'usize' ignored
 // :5:25: note: all non-void values must be used
-// :5:25: note: this error can be suppressed by assigning the value to '_'
+// :5:25: note: to discard the value, assign it to '_'
 // :10:26: error: value of type 'usize' ignored
 // :10:26: note: all non-void values must be used
-// :10:26: note: this error can be suppressed by assigning the value to '_'
+// :10:26: note: to discard the value, assign it to '_'
 // :15:26: error: value of type 'usize' ignored
 // :15:26: note: all non-void values must be used
-// :15:26: note: this error can be suppressed by assigning the value to '_'
+// :15:26: note: to discard the value, assign it to '_'
 // :20:23: error: value of type 'bool' ignored
 // :20:23: note: all non-void values must be used
-// :20:23: note: this error can be suppressed by assigning the value to '_'
+// :20:23: note: to discard the value, assign it to '_'
 // :25:34: error: value of type 'usize' ignored
 // :25:34: note: all non-void values must be used
-// :25:34: note: this error can be suppressed by assigning the value to '_'
+// :25:34: note: to discard the value, assign it to '_'

From 31689d0dd92a683e5ed04facea7bc677ef47785b Mon Sep 17 00:00:00 2001
From: r00ster91 <r00ster91@proton.me>
Date: Fri, 21 Jul 2023 02:30:47 +0200
Subject: [PATCH 2/6] Sema: remove periods from the few error messages that
 have them

For consistency.
---
 src/Sema.zig | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/Sema.zig b/src/Sema.zig
index 3ff817cbd1..123ba93cbe 100644
--- a/src/Sema.zig
+++ b/src/Sema.zig
@@ -9531,7 +9531,7 @@ fn handleExternLibName(
             return sema.fail(
                 block,
                 src_loc,
-                "dependency on dynamic library '{s}' requires enabling Position Independent Code. Fixed by '-l{s}' or '-fPIC'.",
+                "dependency on dynamic library '{s}' requires enabling Position Independent Code; fixed by '-l{s}' or '-fPIC'",
                 .{ lib_name, lib_name },
             );
         }

From 8579904ddd489b73cb61721c31b9e9c14ed9e264 Mon Sep 17 00:00:00 2001
From: r00ster91 <r00ster91@proton.me>
Date: Fri, 21 Jul 2023 02:58:41 +0200
Subject: [PATCH 3/6] Sema: add error note for !?Type types when optional type
 is expected

---
 src/Sema.zig                                    | 17 ++++++++++++++---
 .../while_expected_optional_got_error_union.zig |  1 +
 2 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/src/Sema.zig b/src/Sema.zig
index 123ba93cbe..f286b6385f 100644
--- a/src/Sema.zig
+++ b/src/Sema.zig
@@ -2228,8 +2228,19 @@ fn failWithModRemNegative(sema: *Sema, block: *Block, src: LazySrcLoc, lhs_ty: T
     });
 }
 
-fn failWithExpectedOptionalType(sema: *Sema, block: *Block, src: LazySrcLoc, optional_ty: Type) CompileError {
-    return sema.fail(block, src, "expected optional type, found '{}'", .{optional_ty.fmt(sema.mod)});
+fn failWithExpectedOptionalType(sema: *Sema, block: *Block, src: LazySrcLoc, non_optional_ty: Type) CompileError {
+    const mod = sema.mod;
+    const msg = msg: {
+        const msg = try sema.errMsg(block, src, "expected optional type, found '{}'", .{
+            non_optional_ty.fmt(mod),
+        });
+        errdefer msg.destroy(sema.gpa);
+        if (non_optional_ty.zigTypeTag(mod) == .ErrorUnion) {
+            try sema.errNote(block, src, msg, "consider using 'try', 'catch', or 'if'", .{});
+        }
+        break :msg msg;
+    };
+    return sema.failWithOwnedErrorMsg(block, msg);
 }
 
 fn failWithArrayInitNotSupported(sema: *Sema, block: *Block, src: LazySrcLoc, ty: Type) CompileError {
@@ -9038,7 +9049,7 @@ fn analyzeOptionalPayloadPtr(
 
     const opt_type = optional_ptr_ty.childType(zcu);
     if (opt_type.zigTypeTag(zcu) != .Optional) {
-        return sema.fail(block, src, "expected optional type, found '{}'", .{opt_type.fmt(zcu)});
+        return sema.failWithExpectedOptionalType(block, src, opt_type);
     }
 
     const child_type = opt_type.optionalChild(zcu);
diff --git a/test/cases/compile_errors/while_expected_optional_got_error_union.zig b/test/cases/compile_errors/while_expected_optional_got_error_union.zig
index 7bde2c866d..1b4a64770b 100644
--- a/test/cases/compile_errors/while_expected_optional_got_error_union.zig
+++ b/test/cases/compile_errors/while_expected_optional_got_error_union.zig
@@ -12,3 +12,4 @@ fn bar() anyerror!i32 {
 // target=native
 //
 // :2:15: error: expected optional type, found 'anyerror!i32'
+// :2:15: note: consider using 'try', 'catch', or 'if'

From 9ae43567a3ef14a815482ccaa2a5b412a716743e Mon Sep 17 00:00:00 2001
From: r00ster91 <r00ster91@proton.me>
Date: Fri, 21 Jul 2023 03:22:59 +0200
Subject: [PATCH 4/6] Sema: improve error set/union discard/ignore errors

Previously the error had a note suggesting to use `try`, `catch`, or
`if`, even for error sets where none of those work.
Instead, in case of an error set the way you can handle the error
depends very much on the specific case. For example you might be in a
`catch` where you are discarding or ignoring the error set capture
value, in which case one way to handle the error might be to `return`
the error.
So, in that case, we do not attach that error note.

Additionally, this makes the error tell you what kind of an error it is:
is it an error set or an error union? This distinction is very relevant
in how to handle the error.
---
 src/Sema.zig                                       | 10 ++++++----
 .../compile_errors/discarding_error_value.zig      |  9 +++++++--
 .../ignored_deferred_function_call.zig             | 10 +++++++++-
 .../ignored_expression_in_while_continuation.zig   | 14 +++++++++++---
 4 files changed, 33 insertions(+), 10 deletions(-)

diff --git a/src/Sema.zig b/src/Sema.zig
index f286b6385f..c55531d924 100644
--- a/src/Sema.zig
+++ b/src/Sema.zig
@@ -3568,9 +3568,10 @@ fn ensureResultUsed(
     const mod = sema.mod;
     switch (ty.zigTypeTag(mod)) {
         .Void, .NoReturn => return,
-        .ErrorSet, .ErrorUnion => {
+        .ErrorSet => return sema.fail(block, src, "error set is ignored", .{}),
+        .ErrorUnion => {
             const msg = msg: {
-                const msg = try sema.errMsg(block, src, "error is ignored", .{});
+                const msg = try sema.errMsg(block, src, "error union is ignored", .{});
                 errdefer msg.destroy(sema.gpa);
                 try sema.errNote(block, src, msg, "consider using 'try', 'catch', or 'if'", .{});
                 break :msg msg;
@@ -3600,9 +3601,10 @@ fn zirEnsureResultNonError(sema: *Sema, block: *Block, inst: Zir.Inst.Index) Com
     const src = inst_data.src();
     const operand_ty = sema.typeOf(operand);
     switch (operand_ty.zigTypeTag(mod)) {
-        .ErrorSet, .ErrorUnion => {
+        .ErrorSet => return sema.fail(block, src, "error set is discarded", .{}),
+        .ErrorUnion => {
             const msg = msg: {
-                const msg = try sema.errMsg(block, src, "error is discarded", .{});
+                const msg = try sema.errMsg(block, src, "error union is discarded", .{});
                 errdefer msg.destroy(sema.gpa);
                 try sema.errNote(block, src, msg, "consider using 'try', 'catch', or 'if'", .{});
                 break :msg msg;
diff --git a/test/cases/compile_errors/discarding_error_value.zig b/test/cases/compile_errors/discarding_error_value.zig
index c24d517d3e..eab3ecaf98 100644
--- a/test/cases/compile_errors/discarding_error_value.zig
+++ b/test/cases/compile_errors/discarding_error_value.zig
@@ -1,13 +1,18 @@
-export fn entry() void {
+export fn entry1() void {
     _ = foo();
 }
 fn foo() !void {
     return error.OutOfMemory;
 }
+export fn entry2() void {
+    const x: error{a} = undefined;
+    _ = x;
+}
 
 // error
 // backend=stage2
 // target=native
 //
-// :2:12: error: error is discarded
+// :2:12: error: error union is discarded
 // :2:12: note: consider using 'try', 'catch', or 'if'
+// :9:9: error: error set is discarded
diff --git a/test/cases/compile_errors/ignored_deferred_function_call.zig b/test/cases/compile_errors/ignored_deferred_function_call.zig
index 9537255d33..90c978b40f 100644
--- a/test/cases/compile_errors/ignored_deferred_function_call.zig
+++ b/test/cases/compile_errors/ignored_deferred_function_call.zig
@@ -5,9 +5,17 @@ fn bar() anyerror!i32 {
     return 0;
 }
 
+export fn foo2() void {
+    defer bar2();
+}
+fn bar2() anyerror {
+    return error.a;
+}
+
 // error
 // backend=stage2
 // target=native
 //
-// :2:14: error: error is ignored
+// :2:14: error: error union is ignored
 // :2:14: note: consider using 'try', 'catch', or 'if'
+// :9:15: error: error set is ignored
diff --git a/test/cases/compile_errors/ignored_expression_in_while_continuation.zig b/test/cases/compile_errors/ignored_expression_in_while_continuation.zig
index 4fa396190a..ca1b60da5e 100644
--- a/test/cases/compile_errors/ignored_expression_in_while_continuation.zig
+++ b/test/cases/compile_errors/ignored_expression_in_while_continuation.zig
@@ -15,13 +15,21 @@ fn bad() anyerror!void {
     return error.Bad;
 }
 
+export fn d() void {
+    while (true) : (bad2()) {}
+}
+fn bad2() anyerror {
+    return error.Bad;
+}
+
 // error
 // backend=stage2
 // target=native
 //
-// :2:24: error: error is ignored
+// :2:24: error: error union is ignored
 // :2:24: note: consider using 'try', 'catch', or 'if'
-// :7:25: error: error is ignored
+// :7:25: error: error union is ignored
 // :7:25: note: consider using 'try', 'catch', or 'if'
-// :12:25: error: error is ignored
+// :12:25: error: error union is ignored
 // :12:25: note: consider using 'try', 'catch', or 'if'
+// :19:25: error: error set is ignored

From f14cf13ff8553030c47748a0cbd455514cd1f4a3 Mon Sep 17 00:00:00 2001
From: Wooster <wooster0@proton.me>
Date: Sun, 30 Jul 2023 11:10:41 +0200
Subject: [PATCH 5/6] Sema: suggest using try/catch/if on method call on error
 union

---
 src/Sema.zig                                  |  3 +++
 .../method_call_on_error_union.zig            | 21 +++++++++++++++++++
 2 files changed, 24 insertions(+)
 create mode 100644 test/cases/compile_errors/method_call_on_error_union.zig

diff --git a/src/Sema.zig b/src/Sema.zig
index c55531d924..a5c5f37e4c 100644
--- a/src/Sema.zig
+++ b/src/Sema.zig
@@ -27888,6 +27888,9 @@ fn fieldCallBind(
             const decl = mod.declPtr(decl_idx);
             try mod.errNoteNonLazy(decl.srcLoc(mod), msg, "'{}' is not a member function", .{field_name.fmt(ip)});
         }
+        if (concrete_ty.zigTypeTag(mod) == .ErrorUnion) {
+            try sema.errNote(block, src, msg, "consider using 'try', 'catch', or 'if'", .{});
+        }
         break :msg msg;
     };
     return sema.failWithOwnedErrorMsg(block, msg);
diff --git a/test/cases/compile_errors/method_call_on_error_union.zig b/test/cases/compile_errors/method_call_on_error_union.zig
new file mode 100644
index 0000000000..4ce6b3baa8
--- /dev/null
+++ b/test/cases/compile_errors/method_call_on_error_union.zig
@@ -0,0 +1,21 @@
+const X = struct {
+    fn init() !X {
+        return error.a;
+    }
+
+    fn a(x: X) void {
+        _ = x;
+    }
+};
+
+export fn entry() void {
+    const x = X.init();
+    x.a();
+}
+
+// error
+// backend=stage2
+// target=native
+//
+// :13:6: error: no field or member function named 'a' in '@typeInfo(@typeInfo(@TypeOf(tmp.X.init)).Fn.return_type.?).ErrorUnion.error_set!tmp.X'
+// :13:6: note: consider using 'try', 'catch', or 'if'

From ac55685a94b3db97e9d2eadef0432948b3c16a03 Mon Sep 17 00:00:00 2001
From: wooster0 <wooster0@proton.me>
Date: Wed, 22 May 2024 02:16:56 +0900
Subject: [PATCH 6/6] Sema: add missing declared here note

---
 src/Sema.zig                                     |  1 +
 .../expected_optional_type_got_container.zig     | 16 ++++++++++++++++
 2 files changed, 17 insertions(+)
 create mode 100644 test/cases/compile_errors/expected_optional_type_got_container.zig

diff --git a/src/Sema.zig b/src/Sema.zig
index a5c5f37e4c..7a1885d652 100644
--- a/src/Sema.zig
+++ b/src/Sema.zig
@@ -2238,6 +2238,7 @@ fn failWithExpectedOptionalType(sema: *Sema, block: *Block, src: LazySrcLoc, non
         if (non_optional_ty.zigTypeTag(mod) == .ErrorUnion) {
             try sema.errNote(block, src, msg, "consider using 'try', 'catch', or 'if'", .{});
         }
+        try addDeclaredHereNote(sema, msg, non_optional_ty);
         break :msg msg;
     };
     return sema.failWithOwnedErrorMsg(block, msg);
diff --git a/test/cases/compile_errors/expected_optional_type_got_container.zig b/test/cases/compile_errors/expected_optional_type_got_container.zig
new file mode 100644
index 0000000000..12bb629629
--- /dev/null
+++ b/test/cases/compile_errors/expected_optional_type_got_container.zig
@@ -0,0 +1,16 @@
+export fn foo() void {
+    while (bar()) |x| {
+        _ = x;
+    }
+}
+const X = enum { a };
+fn bar() X {
+    return .a;
+}
+
+// error
+// backend=stage2
+// target=native
+//
+// :2:15: error: expected optional type, found 'tmp.X'
+// :6:11: note: enum declared here