| Message ID | pull.1889.v3.git.1743076383.gitgitgadget@gmail.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | Avoid the comma operator | expand |
Hi Johannes On 27/03/2025 11:52, Johannes Schindelin via GitGitGadget wrote: > > Changes since v2: > > * Made the sed construct in detect-compiler portable (thanks, Eric > Sunshine!) > * The majority of the feedback disagreed with the more compact format in > diff-delta.c, so I changed it to the long format (thanks, Phillip Wood!) > * The more succinct and safer, but less readable, cast in the loop > condition of the dowild() function was replaced with the goto-based > alternative I had mentioned as a possibility in the commit message > (thanks, Phillip Wood!) > * I adjusted the style of my compat/regex/ patch to the surrounding code's. > * The -Wcomma option is now used in Meson-based clang builds, too (thanks, > Patrick Steinhardt!) The range-diff below looks good to me, thanks for making our code base clearer. Best Wishes Phillip > Range-diff vs v2: > > 1: 913c7a0d296 = 1: 913c7a0d296 remote-curl: avoid using the comma operator unnecessarily > 2: 37ff88b8275 = 2: 37ff88b8275 rebase: avoid using the comma operator unnecessarily > 3: f601f4e74a5 = 3: f601f4e74a5 kwset: avoid using the comma operator unnecessarily > 4: f60ebe376e1 = 4: f60ebe376e1 clar: avoid using the comma operator unnecessarily > 5: 7239078413f = 5: 7239078413f xdiff: avoid using the comma operator unnecessarily > 6: 5e0e8325620 ! 6: 045d695d73e diff-delta: explicitly mark intentional use of the comma operator > @@ Metadata > Author: Johannes Schindelin <Johannes.Schindelin@gmx.de> > > ## Commit message ## > - diff-delta: explicitly mark intentional use of the comma operator > + diff-delta: avoid using the comma operator > > The comma operator is a somewhat obscure C feature that is often used by > mistake and can even cause unintentional code flow. That is why the > @@ Commit message > Intentional uses include situations where one wants to avoid curly > brackets around multiple statements that need to be guarded by a > condition. This is the case here, as the repetitive nature of the > - statements is easier to see for a human reader this way. > + statements is easier to see for a human reader this way. At least in my > + opinion. > > - To mark this usage as intentional, the return value of the statement > - before the comma needs to be cast to `void`, which we do here. > + However, opinions on this differ wildly, take 10 people and you have 10 > + different preferences. > > + On the Git mailing list, it seems that the consensus is to use the long > + form instead, so let's do just that. > + > + Suggested-by: Phillip Wood <phillip.wood123@gmail.com> > Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> > > ## diff-delta.c ## > @@ diff-delta.c: create_delta(const struct delta_index *index, > + op = out + outpos++; > i = 0x80; > > - if (moff & 0x000000ff) > +- if (moff & 0x000000ff) > - out[outpos++] = moff >> 0, i |= 0x01; > -+ (void)(out[outpos++] = moff >> 0), i |= 0x01; > - if (moff & 0x0000ff00) > +- if (moff & 0x0000ff00) > - out[outpos++] = moff >> 8, i |= 0x02; > -+ (void)(out[outpos++] = moff >> 8), i |= 0x02; > - if (moff & 0x00ff0000) > +- if (moff & 0x00ff0000) > - out[outpos++] = moff >> 16, i |= 0x04; > -+ (void)(out[outpos++] = moff >> 16), i |= 0x04; > - if (moff & 0xff000000) > +- if (moff & 0xff000000) > - out[outpos++] = moff >> 24, i |= 0x08; > -+ (void)(out[outpos++] = moff >> 24), i |= 0x08; > - > - if (msize & 0x00ff) > +- > +- if (msize & 0x00ff) > - out[outpos++] = msize >> 0, i |= 0x10; > -+ (void)(out[outpos++] = msize >> 0), i |= 0x10; > - if (msize & 0xff00) > +- if (msize & 0xff00) > - out[outpos++] = msize >> 8, i |= 0x20; > -+ (void)(out[outpos++] = msize >> 8), i |= 0x20; > ++ if (moff & 0x000000ff) { > ++ out[outpos++] = moff >> 0; > ++ i |= 0x01; > ++ } > ++ if (moff & 0x0000ff00) { > ++ out[outpos++] = moff >> 8; > ++ i |= 0x02; > ++ } > ++ if (moff & 0x00ff0000) { > ++ out[outpos++] = moff >> 16; > ++ i |= 0x04; > ++ } > ++ if (moff & 0xff000000) { > ++ out[outpos++] = moff >> 24; > ++ i |= 0x08; > ++ } > ++ > ++ if (msize & 0x00ff) { > ++ out[outpos++] = msize >> 0; > ++ i |= 0x10; > ++ } > ++ if (msize & 0xff00) { > ++ out[outpos++] = msize >> 8; > ++ i |= 0x20; > ++ } > > *op = i; > > 7: 9a6de12b807 ! 7: 1d0ce59cb68 wildmatch: explicitly mark intentional use of the comma operator > @@ Metadata > Author: Johannes Schindelin <Johannes.Schindelin@gmx.de> > > ## Commit message ## > - wildmatch: explicitly mark intentional use of the comma operator > + wildmatch: avoid using of the comma operator > > The comma operator is a somewhat obscure C feature that is often used by > mistake and can even cause unintentional code flow. That is why the > `-Wcomma` option of clang was introduced: To identify unintentional uses > of the comma operator. > > - To mark such a usage as intentional, the value needs to be cast to > - `void`, which we do here. > - > In this instance, the usage is intentional because it allows storing the > value of the current character as `prev_ch` before making the next > character the current one, all of which happens in the loop condition > that lets the loop stop at a closing bracket. > > - The alternative to using the comma operator would be to move those > + However, it is hard to read. > + > + The chosen alternative to using the comma operator is to move those > assignments from the condition into the loop body; In this particular > - case that would require the assignments to either be duplicated or to > - introduce and use a `goto` target before the assignments, though, > - because the loop body contains a `continue` for the case where a > - character class is found that starts with `[:` but does not end in `:]` > - (and the assignments should occur even when that code path is taken). > + case that requires special care because the loop body contains a > + `continue` for the case where a character class is found that starts > + with `[:` but does not end in `:]` (and the assignments should occur > + even when that code path is taken), which needs to be turned into a > + `goto`. > > + Helped-by: Phillip Wood <phillip.wood@dunelm.org.uk> > Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> > > ## wildmatch.c ## > +@@ wildmatch.c: static int dowild(const uchar *p, const uchar *text, unsigned int flags) > + p_ch = '['; > + if (t_ch == p_ch) > + matched = 1; > +- continue; > ++ goto next; > + } > + if (CC_EQ(s,i, "alnum")) { > + if (ISALNUM(t_ch)) > @@ wildmatch.c: static int dowild(const uchar *p, const uchar *text, unsigned int flags) > p_ch = 0; /* This makes "prev_ch" get set to 0. */ > } else if (t_ch == p_ch) > matched = 1; > - } while (prev_ch = p_ch, (p_ch = *++p) != ']'); > -+ } while ((void)(prev_ch = p_ch), (p_ch = *++p) != ']'); > ++next: > ++ prev_ch = p_ch; > ++ p_ch = *++p; > ++ } while (p_ch != ']'); > if (matched == negated || > ((flags & WM_PATHNAME) && t_ch == '/')) > return WM_NOMATCH; > 8: dc626f36df3 ! 8: b8405f3d237 compat/regex: explicitly mark intentional use of the comma operator > @@ Commit message > > ## compat/regex/regex_internal.c ## > @@ compat/regex/regex_internal.c: re_node_set_merge (re_node_set *dest, const re_node_set *src) > - for (sbase = dest->nelem + 2 * src->nelem, > is = src->nelem - 1, id = dest->nelem - 1; is >= 0 && id >= 0; ) > { > -- if (dest->elems[id] == src->elems[is]) > + if (dest->elems[id] == src->elems[is]) > - is--, id--; > -- else if (dest->elems[id] < src->elems[is]) > -+ if (dest->elems[id] == src->elems[is]) { > -+ is--; > -+ id--; > -+ } else if (dest->elems[id] < src->elems[is]) > ++ { > ++ is--; > ++ id--; > ++ } > + else if (dest->elems[id] < src->elems[is]) > dest->elems[--sbase] = src->elems[is--]; > else /* if (dest->elems[id] > src->elems[is]) */ > - --id; > > ## compat/regex/regexec.c ## > @@ compat/regex/regexec.c: sift_states_bkref (const re_match_context_t *mctx, re_sift_context_t *sctx, > 9: 91f86c3aba9 ! 9: 6b6cd556465 clang: warn when the comma operator is used > @@ Commit message > warn about code using the comma operator (because it is typically > unintentional and wants to use the semicolon instead). > > + Helped-by: Patrick Steinhardt <ps@pks.im> > Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> > > ## config.mak.dev ## > @@ config.mak.dev: DEVELOPER_CFLAGS += -Wvla > ifneq ($(filter clang4,$(COMPILER_FEATURES)),) > DEVELOPER_CFLAGS += -Wtautological-constant-out-of-range-compare > endif > + > + ## meson.build ## > +@@ meson.build: libgit_dependencies = [ ] > + # Makefile. > + if get_option('warning_level') in ['2','3', 'everything'] and compiler.get_argument_syntax() == 'gcc' > + foreach cflag : [ > ++ '-Wcomma', > + '-Wdeclaration-after-statement', > + '-Wformat-security', > + '-Wold-style-definition', > 10: 2f6f31240fe ! 10: 77f1dcaca1c detect-compiler: detect clang even if it found CUDA > @@ Commit message > Let's unconfuse the script by letting it parse the first matching line > and ignore the rest. > > + Helped-by: Eric Sunshine <sunshine@sunshineco.com> > Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> > > ## detect-compiler ## > @@ detect-compiler: CC="$*" > # FreeBSD clang version 3.4.1 (tags/RELEASE...) > get_version_line() { > - LANG=C LC_ALL=C $CC -v 2>&1 | grep ' version ' > -+ LANG=C LC_ALL=C $CC -v 2>&1 | sed -n '/ version /{p;q}' > ++ LANG=C LC_ALL=C $CC -v 2>&1 | sed -n '/ version /{p;q;}' > } > > get_family() { >
Phillip Wood <phillip.wood123@gmail.com> writes: > Hi Johannes > > On 27/03/2025 11:52, Johannes Schindelin via GitGitGadget wrote: >> Changes since v2: >> * Made the sed construct in detect-compiler portable (thanks, Eric >> Sunshine!) >> * The majority of the feedback disagreed with the more compact format in >> diff-delta.c, so I changed it to the long format (thanks, Phillip Wood!) >> * The more succinct and safer, but less readable, cast in the loop >> condition of the dowild() function was replaced with the goto-based >> alternative I had mentioned as a possibility in the commit message >> (thanks, Phillip Wood!) >> * I adjusted the style of my compat/regex/ patch to the surrounding code's. >> * The -Wcomma option is now used in Meson-based clang builds, too (thanks, >> Patrick Steinhardt!) > > The range-diff below looks good to me, thanks for making our code base > clearer. > > Best Wishes > > Phillip Yup, thanks Dscho, and all who gave valuable input to polish the series. Will queue.
The comma operator [https://en.cppreference.com/w/c/language/operator_other#Comma_operator] is rarely used in C anymore, and typically indicates a typo. Just like in these instances, where a semicolon was meant to be used, as there is no need to discard the first statement's result here. Changes since v2: * Made the sed construct in detect-compiler portable (thanks, Eric Sunshine!) * The majority of the feedback disagreed with the more compact format in diff-delta.c, so I changed it to the long format (thanks, Phillip Wood!) * The more succinct and safer, but less readable, cast in the loop condition of the dowild() function was replaced with the goto-based alternative I had mentioned as a possibility in the commit message (thanks, Phillip Wood!) * I adjusted the style of my compat/regex/ patch to the surrounding code's. * The -Wcomma option is now used in Meson-based clang builds, too (thanks, Patrick Steinhardt!) Changes since v1: * Use -Wcomma when compiling with clang and with DEVELOPER=1. * Address the remaining instances pointed out by clang (and by Phillip). Johannes Schindelin (10): remote-curl: avoid using the comma operator unnecessarily rebase: avoid using the comma operator unnecessarily kwset: avoid using the comma operator unnecessarily clar: avoid using the comma operator unnecessarily xdiff: avoid using the comma operator unnecessarily diff-delta: avoid using the comma operator wildmatch: avoid using of the comma operator compat/regex: explicitly mark intentional use of the comma operator clang: warn when the comma operator is used detect-compiler: detect clang even if it found CUDA builtin/rebase.c | 2 +- compat/regex/regex_internal.c | 5 +++- compat/regex/regexec.c | 2 +- config.mak.dev | 4 +++ detect-compiler | 2 +- diff-delta.c | 38 +++++++++++++++--------- kwset.c | 54 +++++++++++++++++++---------------- meson.build | 1 + remote-curl.c | 4 +-- t/unit-tests/clar/clar/fs.h | 10 +++++-- wildmatch.c | 7 +++-- xdiff/xdiffi.c | 12 +++++--- 12 files changed, 89 insertions(+), 52 deletions(-) base-commit: 683c54c999c301c2cd6f715c411407c413b1d84e Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1889%2Fdscho%2Fcomma-operator-v3 Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1889/dscho/comma-operator-v3 Pull-Request: https://github.com/gitgitgadget/git/pull/1889 Range-diff vs v2: 1: 913c7a0d296 = 1: 913c7a0d296 remote-curl: avoid using the comma operator unnecessarily 2: 37ff88b8275 = 2: 37ff88b8275 rebase: avoid using the comma operator unnecessarily 3: f601f4e74a5 = 3: f601f4e74a5 kwset: avoid using the comma operator unnecessarily 4: f60ebe376e1 = 4: f60ebe376e1 clar: avoid using the comma operator unnecessarily 5: 7239078413f = 5: 7239078413f xdiff: avoid using the comma operator unnecessarily 6: 5e0e8325620 ! 6: 045d695d73e diff-delta: explicitly mark intentional use of the comma operator @@ Metadata Author: Johannes Schindelin <Johannes.Schindelin@gmx.de> ## Commit message ## - diff-delta: explicitly mark intentional use of the comma operator + diff-delta: avoid using the comma operator The comma operator is a somewhat obscure C feature that is often used by mistake and can even cause unintentional code flow. That is why the @@ Commit message Intentional uses include situations where one wants to avoid curly brackets around multiple statements that need to be guarded by a condition. This is the case here, as the repetitive nature of the - statements is easier to see for a human reader this way. + statements is easier to see for a human reader this way. At least in my + opinion. - To mark this usage as intentional, the return value of the statement - before the comma needs to be cast to `void`, which we do here. + However, opinions on this differ wildly, take 10 people and you have 10 + different preferences. + On the Git mailing list, it seems that the consensus is to use the long + form instead, so let's do just that. + + Suggested-by: Phillip Wood <phillip.wood123@gmail.com> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> ## diff-delta.c ## @@ diff-delta.c: create_delta(const struct delta_index *index, + op = out + outpos++; i = 0x80; - if (moff & 0x000000ff) +- if (moff & 0x000000ff) - out[outpos++] = moff >> 0, i |= 0x01; -+ (void)(out[outpos++] = moff >> 0), i |= 0x01; - if (moff & 0x0000ff00) +- if (moff & 0x0000ff00) - out[outpos++] = moff >> 8, i |= 0x02; -+ (void)(out[outpos++] = moff >> 8), i |= 0x02; - if (moff & 0x00ff0000) +- if (moff & 0x00ff0000) - out[outpos++] = moff >> 16, i |= 0x04; -+ (void)(out[outpos++] = moff >> 16), i |= 0x04; - if (moff & 0xff000000) +- if (moff & 0xff000000) - out[outpos++] = moff >> 24, i |= 0x08; -+ (void)(out[outpos++] = moff >> 24), i |= 0x08; - - if (msize & 0x00ff) +- +- if (msize & 0x00ff) - out[outpos++] = msize >> 0, i |= 0x10; -+ (void)(out[outpos++] = msize >> 0), i |= 0x10; - if (msize & 0xff00) +- if (msize & 0xff00) - out[outpos++] = msize >> 8, i |= 0x20; -+ (void)(out[outpos++] = msize >> 8), i |= 0x20; ++ if (moff & 0x000000ff) { ++ out[outpos++] = moff >> 0; ++ i |= 0x01; ++ } ++ if (moff & 0x0000ff00) { ++ out[outpos++] = moff >> 8; ++ i |= 0x02; ++ } ++ if (moff & 0x00ff0000) { ++ out[outpos++] = moff >> 16; ++ i |= 0x04; ++ } ++ if (moff & 0xff000000) { ++ out[outpos++] = moff >> 24; ++ i |= 0x08; ++ } ++ ++ if (msize & 0x00ff) { ++ out[outpos++] = msize >> 0; ++ i |= 0x10; ++ } ++ if (msize & 0xff00) { ++ out[outpos++] = msize >> 8; ++ i |= 0x20; ++ } *op = i; 7: 9a6de12b807 ! 7: 1d0ce59cb68 wildmatch: explicitly mark intentional use of the comma operator @@ Metadata Author: Johannes Schindelin <Johannes.Schindelin@gmx.de> ## Commit message ## - wildmatch: explicitly mark intentional use of the comma operator + wildmatch: avoid using of the comma operator The comma operator is a somewhat obscure C feature that is often used by mistake and can even cause unintentional code flow. That is why the `-Wcomma` option of clang was introduced: To identify unintentional uses of the comma operator. - To mark such a usage as intentional, the value needs to be cast to - `void`, which we do here. - In this instance, the usage is intentional because it allows storing the value of the current character as `prev_ch` before making the next character the current one, all of which happens in the loop condition that lets the loop stop at a closing bracket. - The alternative to using the comma operator would be to move those + However, it is hard to read. + + The chosen alternative to using the comma operator is to move those assignments from the condition into the loop body; In this particular - case that would require the assignments to either be duplicated or to - introduce and use a `goto` target before the assignments, though, - because the loop body contains a `continue` for the case where a - character class is found that starts with `[:` but does not end in `:]` - (and the assignments should occur even when that code path is taken). + case that requires special care because the loop body contains a + `continue` for the case where a character class is found that starts + with `[:` but does not end in `:]` (and the assignments should occur + even when that code path is taken), which needs to be turned into a + `goto`. + Helped-by: Phillip Wood <phillip.wood@dunelm.org.uk> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> ## wildmatch.c ## +@@ wildmatch.c: static int dowild(const uchar *p, const uchar *text, unsigned int flags) + p_ch = '['; + if (t_ch == p_ch) + matched = 1; +- continue; ++ goto next; + } + if (CC_EQ(s,i, "alnum")) { + if (ISALNUM(t_ch)) @@ wildmatch.c: static int dowild(const uchar *p, const uchar *text, unsigned int flags) p_ch = 0; /* This makes "prev_ch" get set to 0. */ } else if (t_ch == p_ch) matched = 1; - } while (prev_ch = p_ch, (p_ch = *++p) != ']'); -+ } while ((void)(prev_ch = p_ch), (p_ch = *++p) != ']'); ++next: ++ prev_ch = p_ch; ++ p_ch = *++p; ++ } while (p_ch != ']'); if (matched == negated || ((flags & WM_PATHNAME) && t_ch == '/')) return WM_NOMATCH; 8: dc626f36df3 ! 8: b8405f3d237 compat/regex: explicitly mark intentional use of the comma operator @@ Commit message ## compat/regex/regex_internal.c ## @@ compat/regex/regex_internal.c: re_node_set_merge (re_node_set *dest, const re_node_set *src) - for (sbase = dest->nelem + 2 * src->nelem, is = src->nelem - 1, id = dest->nelem - 1; is >= 0 && id >= 0; ) { -- if (dest->elems[id] == src->elems[is]) + if (dest->elems[id] == src->elems[is]) - is--, id--; -- else if (dest->elems[id] < src->elems[is]) -+ if (dest->elems[id] == src->elems[is]) { -+ is--; -+ id--; -+ } else if (dest->elems[id] < src->elems[is]) ++ { ++ is--; ++ id--; ++ } + else if (dest->elems[id] < src->elems[is]) dest->elems[--sbase] = src->elems[is--]; else /* if (dest->elems[id] > src->elems[is]) */ - --id; ## compat/regex/regexec.c ## @@ compat/regex/regexec.c: sift_states_bkref (const re_match_context_t *mctx, re_sift_context_t *sctx, 9: 91f86c3aba9 ! 9: 6b6cd556465 clang: warn when the comma operator is used @@ Commit message warn about code using the comma operator (because it is typically unintentional and wants to use the semicolon instead). + Helped-by: Patrick Steinhardt <ps@pks.im> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> ## config.mak.dev ## @@ config.mak.dev: DEVELOPER_CFLAGS += -Wvla ifneq ($(filter clang4,$(COMPILER_FEATURES)),) DEVELOPER_CFLAGS += -Wtautological-constant-out-of-range-compare endif + + ## meson.build ## +@@ meson.build: libgit_dependencies = [ ] + # Makefile. + if get_option('warning_level') in ['2','3', 'everything'] and compiler.get_argument_syntax() == 'gcc' + foreach cflag : [ ++ '-Wcomma', + '-Wdeclaration-after-statement', + '-Wformat-security', + '-Wold-style-definition', 10: 2f6f31240fe ! 10: 77f1dcaca1c detect-compiler: detect clang even if it found CUDA @@ Commit message Let's unconfuse the script by letting it parse the first matching line and ignore the rest. + Helped-by: Eric Sunshine <sunshine@sunshineco.com> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> ## detect-compiler ## @@ detect-compiler: CC="$*" # FreeBSD clang version 3.4.1 (tags/RELEASE...) get_version_line() { - LANG=C LC_ALL=C $CC -v 2>&1 | grep ' version ' -+ LANG=C LC_ALL=C $CC -v 2>&1 | sed -n '/ version /{p;q}' ++ LANG=C LC_ALL=C $CC -v 2>&1 | sed -n '/ version /{p;q;}' } get_family() {