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linzhp
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Nov 4, 2021
linzhp
reviewed
Nov 8, 2021
The coverage support in the builder works in the following way:
1. Run `go tool cover` to create an instrumented source file, for example:
```
$ go test -work -cover database/sql
WORK=/var/folders/yf/4v4h0_t53h30t_8vc90d1gx40000gp/T/go-build105184680/
$ find $WORK -name *cover.go
...
$ less /var/folders/yf/4v4h0_t53h30t_8vc90d1gx40000gp/T/go-build105184680//b059/sql.cover.go
...
func Register(name string, driver driver.Driver) {GoCover_2_343132323961636265643234.Count[0] = 1;
driversMu.Lock()
defer driversMu.Unlock()
if driver == nil {GoCover_2_343132323961636265643234.Count[3] = 1;
panic("sql: Register driver is nil")
}
GoCover_2_343132323961636265643234.Count[1] = 1;if _, dup := drivers[name]; dup {GoCover_2_343132323961636265643234.Count[4] = 1;
panic("sql: Register called twice for driver " + name)
}
GoCover_2_343132323961636265643234.Count[2] = 1;drivers[name] = driver
}
...
// appended to end of file
var GoCover_2_343132323961636265643234 = struct {
Count [727]uint32
Pos [3 * 727]uint32
NumStmt [727]uint16
} {
...
```
2. Register each file's coverage (above, `GoCover_2_343132323961636265643234`) with
[coverdata](https://pkg.go.dev/github.com/bazelbuild/rules_go@v0.29.0/go/tools/coverdata).
This requires adding or updating an import for that package and calling `RegisterFile` in `init()`.
This is done by using `go/parser` and `go/ast` to modify the AST and `go/format` to print it
back out to the instrumented source file.
The problem is that this changes line numbers, resulting in panics
that no longer identify the correct stack trace.
`go tool cover` avoids this issue because it places the coverage
variable increments on the same line as control flow branch of
interest to avoid this problem, which it accomplishes by using the
[cmd/internal/edit](https://pkg.go.dev/cmd/internal/edit@go1.17.3)
package.
This change brings that approach to rules_go coverage instrumentation:
1. Copy in the cmd/internal/edit package for bytebuffer-based
editing.
2. Update the `registerCoverage` step to use that instead of AST
modifications & `go/format`.
Fixes #2990
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This copies in Go's cmd/internal/edit package for bytebuffer-based
editing.
Fixes #2990